Oznaka poročila: ARRS-RPROJ-ZP-2011-1/57 ZAKLJUČNO POROČILO O REZULTATIH RAZISKOVALNEGA PROJEKTA A. PODATKI O RAZISKOVALNEM PROJEKTU 1. Osnovni podatki o raziskovalnem projektu Šifra projekta J7-0363 Naslov projekta Naravni in antropogeni sevalci gama in beta v podzemnih vodah Slovenije Vodja projekta 2586 Matjaž Aleš Korun Tip projekta J Temeljni projekt Obseg raziskovalnih ur 4.170 Cenovni razred D Trajanje projekta 02.2008 - 01.2011 Nosilna raziskovalna organizacija 106 Institut "Jožef Stefan" Raziskovalne organizacije -soizvajalke 215 Geološki zavod Slovenije 6484 JAVNO PODJETJE VODOVOD-KANALIZACIJA, d.o.o. Družbenoekonomski cilj 13. Splošni napredek znanja - RiR financiran iz drugih virov (ne iz splošnih univerzitetnih fondov - SUF) . Družbeno-ekonomski cilj1 Šifra 01. Naziv Raziskovanje in izkoriščanje zemlje 2. Sofinancerji2 1. Naziv Naslov 2. Naziv Naslov 3. Naziv Naslov B. REZULTATI IN DOSEŽKI RAZISKOVALNEGA PROJEKTA 3. Poročilo o realizaciji programa raziskovalnega projekta3 Vzorčevanje V spomladanskem in jesenskem obdobju v letu 2010 je bilo izvedeno vzorčenje podzemne vode na različnih merilnih mestih v Sloveniji. Mreža vzorčnih mest je bila sestavljena iz izvirov, piezometrov, črpališč pitne vode, privatnih vodnjakov in deževnice. Spomladi je vzorčenje potekalo 43 vzorčnih mestih za analizo gama sevalcev ter na 45 vzorčnih mestih za analizo tritija v podzemni vodi, v jesenskem obdobju pa na 28 vzorčnih mestih za analizo gama sevalcev in analizo tritija v podzemni vodi. Število vzorcev, zbranih tekom izvajanje projekta je v sledeči tabeli. Leto Število vzorcev Spektrometrija gama Število vzorcev Scintilacijska spektrometrija 2008 10 13 2009 1. polletje 48 57 2. polletje 39 46 2010 1. polletje 43 44 2. polletje 28 28 Vzorci so bili odvzeti zbrani na 81 različnih lokacijah za spektrometrijo gama in na 91 lokacijah za meritve tritija. Vzorčenje je na piezometrih, črpališčih ter privatnih vodnjakih potekalo z uporabo potopne črpalke s pretokom 0,2 l/s. Pred vzorčenjem se je iz vsakega objekta izčrpalo vsaj 1-kratni volumen stoječega vodnega stolpca ter se s tem omogočil dotok sveže vode. Med prečrpavanjem podzemne vode smo izvedli večkratne meritve fizikalno-kemijskih parametrov: električna prevodnost, pH ter temperatura vode. Ko so se merjeni parametri stabilizirali smo odvzeli vzorce vode. Vzorce izvirov smo zajeli čim bližje iztoku podzemne vode na površje. Za analizo gama sevalcev smo napolnili 50 l sod ter dodali nakisali s HNO3 na pH 2 ali manj. Za analizo tritija smo napolnili 2 plastenki po 1 l. Poleg analiz gama sevalcev in tritija so bili odvzeti tudi vzorci za osnovne fizikalno-kemijske parametre v podzemni vodi: stabilni izotopi (515N, 513C, 518O, 52D), osnovna kemija (Fe, Ca, Mg, Na, K, NH4, HCO3, kloridi, nitrati, sulfati, fosfati) in mikroelementi (Ag, Al, As, Au, B, Ba, Be, Bi, Br, Ca, Cd, Ce, Cl, Co, Cr, Cs, Cu, Dy, Er, Eu, Fe, Ga, Gd, Ge, Hf, Hg, Ho, In, Ir, K, La, Li, Lu, Mg, Mn, Mo, Na, Nb, Nd, Ni, Os, P, Pb, Pd, Pr, Pt, Rb, Re, Rh, Ru, S, Sb, Sc, Se, Si, Sm, Sn, Sr, Ta, Tb, Te, Th, Ti, Tl, Tm, U, V, W, Y, Yb, Zn, Zr). Tekočinskoscintilacijska spektrometrija Meritve V okviru projekta je bilo izmerjenih in izračunanih 165 vzorcev podzemnih vod in deževnice, od tega je 62 rezultatov povprečje dveh neodvisnih analitskih metod. 12 vzorcev je bilo pomerjenih tudi v drugih laboratorijih (Univerza v Krakowu, Poljska in Institut Euder Boškovic, Zagreb, Hrvatska). Rezultati so primerljivi in bodo predstavljeni na konferenci na Krku v sredini aprila 2011, prispevek je sprejet v objavo (Barešic 2011). Vrednosti za H-3 se gibljejo med 0 in 1400 Bq / m3. Največ vzorcev (37) je med 688 in 788 Bq/m3. Rezultati bodo podrobneje predstavljeni in obdelani v okviru doktorata Katarine Kovačič. Izboljšava analitske metode Metoda za določevanje tritija po elektrolitski obogatitvi (Rozanski 2003) v izračunu ne zajema nekaterih tehničnih parametrov priprave vzorcev, ki lahko vplivajo na končno vrednost, zato na njihov račun povečamo negotovost rezultata. Pri datiranju vod si poleg čim nižje meje detekcije prizadevamo tudi za čim manjšo negotovost rezultata, saj bo tako določevanje starosti vod natančnejše. Izvedli smo vrsto poskusov, s katerimi smo podrobno študirali različne dejavnike, ki lahko vplivajo na končni izračun aktivnosti. Delni rezultati so bili predstavljeni na konferenci o LSC spektrometriji v Parizu (Kožar Logar 2010), ostali bodo podrobneje obdelani v sklopu doktorske disertacije mlade raziskovalke Katarine Kovačič, katere usposabljanje še teče. Spektrometrija gama Meritve s spektrometrijo gama še niso zaključene, ker je treba vzorce meriti dvakrat. Na vzorcih iz leta 2010 je treba izvesti še 58 meritev. Te meritve bomo opravili v okviru dveh doktorskih disertacij. Prav tako bomo v okviru disertacij ovrednotili rezultate in jih objavili. Meritve vodnih vzorcev iz okolja s spektrometrijo gama so težavne, ker je koncentracija sevalcev v vodi razmeroma majhna, spektrometrija gama pa ni posebno občutljiva metoda, v primerjavi z metodami ki vključujejo radiokemijsko pripravo vzorca. Da bi izboljšali občutljivost, za pripravo merjenca uporabimo večjo količino zbranega vzorca, približno 50 L. Zbrane vzorce izparimo in merimo aktivnost suhega ostanka. Koncentracija mineralnih snovi v površinskih vodah je okrog 0.05 %, zato z izparevanjem koncentriramo radioaktivno kontaminacijo vode za faktor 2000 in pridobimo okrog 30 g suhega ostanka. Vkljub temu je aktivnost merjenca tako nizka, da predstavljajo problemi meritev in tolmačenja merskih rezultatov v bližini detekcijske meje glavno težavo. Za meritve uporabljamo le en, najobčutljivejši, spektrometer, meritev enega vzorca pa traja dva dni. Vsak vzorec pomerimo dvakrat, enkrat čim prej po vzorčevanju in po nekaj mesecih, da lahko iz časovne odvisnosti ocenimo koncentracijo Th-234 in z dvakratno meritvijo povečamo zanesljivost rezultatov. Probleme tolmačenja rezultatov in rešitve smo objavili v člankih "Interpretation of measurement results near the detection limit in gamma-ray spectrometry using Bayesian statistisc", "Probability for Type I errors in gamma-ray spectrometric measurements of drinking water samples" in "Determination of 238U in ground-water samples using gamma-ray spectrometry". Zaključek Problematiko meritev Ra-226 pri nizkih koncentracijah smo obravanvali v delu "Background daughters in gamma-ray spectrometric measurements,", predstavljenem na konferenci "Environmental Radioactivity" v Rimu in v delu "A comparative study of the radon-induced background in low-level gamma-ray spectrometry", ki je poslano v objavo. Preliminarne merske rezultate smo objavili v prispevku "Tritium and gamma emitters in Slovenian groundwater" na konferenci LCS 2010, International Conference on Advances in Liquid Scientillation v Parizu in v prispevku "Concentration of tritium and members of the uranium and thorium decay chains in ground water in Slovenia and their implications for managing ground water resources" na konferenci International Symposium on Isotopes in Hydrology, Marine Ecosystems, and Climate Change Studies v Monaku. Rokopisi vseh še neobjavljenih prispevkov so v priponkah. Prav tako so v priponki merski rezultati. Povzetek Vsi vzorci, predvideni v projektu, so bili zbrani. Meritve še niso končane zaradi nezadostnih merskih kapacitet in ker je vzorce treba meriti večkrat. Meritve se nadaljujejo v okviru dveh doktorskih disertacij. Vse objave, napovedane v poročilu za leto 2009 so realizirane. V objavo so poslana štiri dela, eno delo je v postopku priprave na objavo. 4. Ocena stopnje realizacije zastavljenih raziskovalnih ciljev4 Ocenjujemo, da smo dosegli raziskovalne cilje, zastavljene v projektu. Vse objave, napovedane v poročilu za leto 2009 so realizirane. Delo bomo nadaljevali v okviru doktorskih disertacij, ki se bodo izvajale še dve leti, na vzorčrvanju, meritvah zbranih vzorcev, pred vsem pa na izpopolnjevanju metodologije za interpretiranje rezultatov v bližini detekcijske meje, interpretacijo samih merskih rezultatov in objavljanjem publikacij. 5. Utemeljitev morebitnih sprememb programa raziskovalnega projekta oziroma sprememb, povečanja ali zmanjšanja sestave projektne skupine5 Spremembe niso predvidene. 6. Najpomembnejši znanstveni rezultati projektne skupine6 Znanstveni rezultat 1. Naslov SLO Interpretacija merskih rezultatov v bližini detekcijske meje v spektrometriji gama z Bayseiansko statistiko ANG Interpretation of measurement results near the detection limit in gamma-ray spectrometry using Bayesian statistics Opis SLO Zahteva, da prava vrednost aktivnosti ne more biti negativna uporabimo za transformiranje izmerkov , ki so lahko pozitivni ali negativni v pričakovane vrednosti. Verjetnostna porazdelitev aktivnosti je odsekana normalna porazdelitev, pričakovano vrednost variance prave vrednosti pa dobimo iz izmerka in njegove negotovosti. Pokažemo, da je standardna deviacija prave vrednosti manjša od negotovosti izmerka in da je razmerje med standardno devijacijo pričakovane vrednosti in pričakovano vrednostjo samo manj kot ena. Ker je pričakovana vrednost vedno večja od izmerka izboljšamo rezultat. ANG The requirement that the true value of an anctivity cannot be negative is used for transformation of raw observed values into expected activity values. The probability distribution of the activity values is a truncated normal distribution and the expected value and the variance of the activity value are derived from the observed value and its standard deviation. It has been shown that the standard deviation of the activity value is less than the standard deviation of the observed value and that the ratio of the standard deviation of the activity value and the expected value is less than one. Objavljeno v KORUN, Matjaž, MAVER, Petra. Interpretation of the measurement results near the detection limit in gamma-ray spectrometry using Bayesian statistics. Accred. Qual. Assur. 2010, 15, 515-520 Tipologija 1.01 Izvirni znanstveni članek COBISS.SI-ID 23900967 2. Naslov SLO Verjetnost za napake tipa I pri meritvah vzorcev pitne vode s spektrometrijo gama ANG Probability for Type I errors in gamma-ray spectrometric measurementrs of drinking water samples Opis SLO V spektrih žarkov gama, ki so bili izmerjeni v odsotnosti vzorca, se pojavijo vrhovi, ki pripadajo ozadju spektrometra. Če merimo vzorce, ki vsebujejo radionuklide, ki nastopajo tudi v ozadju, in imajo aktivnosti v bližini detekcijske meje, prispeva ozadje znatno k ploščini vrhov. Verjetnosti za napačno identificirane radionuklide z mejami za odločitve so podane za radionuklide, ki se pojavijo v ozadju spektrometrov. Za nekatere radionuklide, ki ne nastopajo v ozadju prav tako podajamo verjetnosti za napačno identifikacijo. ANG In gamma-ray spectra, acquired in the absence of the sample, peaks occor which belong to the spectrometer background. When samples are measured, which contain radionuclide that appear in the background also and have activities near the detection level, the background contributes substantially to the peak areas. The probabilities for false positives together with the decision thresholds are given for radionuclides appearing in the background spectra. For some radionuclides that do not appear in the background spectra, probabilities for false detection are given as well. Objavljeno v KORUN, Matjaž, KOVAČIČ, Katarina, VODENIK, Branko. Probability for type I errors in gamma-ray spectrometric measurements of drinking water samples. J. Radioanal. Nucl. Chem 2010, 286, 553-556 Tipologija 1.01 Izvirni znanstveni članek COBISS.SI-ID 24131111 3. Naslov SLO Določanje 238U v vzorcih podzemnih vod s spektrometrijo gama ANG Determination of 238U in ground-water samples using gamma-ray spectrometry Opis SLO Opisan je postopek za meritve nizkih koncentracij 238U v vodi. Vzorce z volumnom 50 L smo izpareli in merili suhi ostanek. Po tem postopku smo pridobili okrog 30 g suhega ostanka. Mejo za odločitev za meritve s spektrometrijo gama smo ocenili na 1.5 Bq/m3. V 26 vzorcih smo izmerili koncentracije do 20 Bq/m3. Večina merskih rezultatov leži v območju okrog 5 Bq/m3. ANG A method for measuring the low-activity concentration of 238U in water is described. Samples of 50 L were evaporated and the dry residue after evaporation was measured. Typically, 30 g of material was obtained for the samples processed in this way. The decision threshold resulting from gamma-ray spectrometric measurements was assessed to 1.5 Bq/m3. A total od 26 samples of ground awter were processed and activity concentrations up to 20 Bq/m3 were measured. However, most of the results were in the range arround 5 Bq/m3. Objavljeno v KORUN, Matjaž, KOVAČIČ, Katarina. Determination of the [sup](238)U in ground-water samples using gamma-ray spectrometry. Appl. Radiat. Isot. 2011, 69, 636-640 Tipologija 1.01 Izvirni znanstveni članek COBISS.SI-ID 24321319 4. Naslov SLO Ozadje radonovih potomcev v meritvah spektrometrije gama ANG Background of radon daughters in gamma-ray spectrometric measurements Opis SLO K ozadju radonovih potomcev prispevajo razni viri, ki so na raznih delih spektrometra. Ozadje spektrometra zaradi radonovih potomcev izvira iz 226Ra v detektorju in ščitu, prisotnosti radonovih potomcev v zraku v notranjosti ščita in v nepopolni atenuaciji žarkov, ki prihajajo iz okolice spektrometra. Ugotovili smo, da je pri nekaterih detektorjih ozadje zaradi radonovih potomcev od časa neodvisno, pri nekaterih pa je korelirano z zunanjo temperaturo. ANG The background due to radon daughters originates from various sources, characterized by the location of radon daughters in the spectrometer. The spectrometer background due to radon daughters originates in the presence of 226Ra in the detector and the shielding, the presence of radon daughters in the air filling the shield's cavity and in the incomplete attenuation of gamma-rays from the environment where the shield is situated. It was found that in some detectors background induced by radon daughters is constant in time whereas in others it exhibits correlation with outside temperature. Objavljeno v MAVER, Petra, KORUN, Matjaž, MARTELANC, Matej, VODENIK, Branko. Background of radon daughters in gamma-ray spectrometric measurements. V: Enviroinmental radioactivity 2010, 25-27 October 2010, Rome, Italy. Book of abstracts : new frontiers and developments. Tipologija 1.08 Objavljeni znanstveni prispevek na konferenci COBISS.SI-ID 24430631 5. Naslov SLO Tritij in sevalci gama v podzemnih vodah Slovenije ANG Tritium and gamma emitters in Slovenian groundawter Opis SLO V podzemskih vodah Slovenije smo izmerili koncentracije tritija, sevalcev gama v uranovem in torijevem razpadnem nizu (U-238, Th-234, Pb-210, Ra-228 in Th-228) in kalija. Opazili smo korelacije med koncentracijami Ra-226, Ra-228 in Th-228 v vzorcih iz medzrnskih in razpoklinskih vodonosnikov. Opazili smo tudi, da je razpon koncentracij tritija v medzrnskih vodonosnikih največji, najmanjši pa v razpoklinskih. ANG Concentrations of tritium, gamma-ray emitters in the uranium and thorium decay chains (U-238, Th-234, Pb-210, Ra-228, Ra-226 and Th-228) and potassium were measured in samples of ground water in Slovenia. Correlations among Ra-226, Ra-228 and Th-228 were observed in samples from intergranular and fractured aquifers. It was also found that the variability of tritium activity in intergranular aquifers is the largerestand in fractured ones the smallest. Objavljeno v KOVAČIČ, Katarina, KOŽAR LOGAR, Jasmina, KORUN, Matjaž. Tritium and gamma emitters in Slovenian groundwater. LSC 2010, International Conference on Advences on Liquid Scintillation spectrometry, September 610, Paris, France. Programme and abstracts. Tipologija 1.08 Objavljeni znanstveni prispevek na konferenci COBISS.SI-ID 24327207 7. Najpomembnejši družbeno-ekonomsko relevantni rezultati projektne skupine6 Družbeno-ekonomsko relevantni rezultat 1. Naslov SLO Vodenje projekta INCOME (LIFE07/SLO/ENV/000725) ANG Management of INCOME project (LIFE07/SLO/ENV/000725) Opis SLO Namen projekta INCOME je vzpostavitev postopkov za učinkovito upravljanje z onesnaženimi vodonosniki. Projekt povezuje postopke za odkrivanje in nadzor virov onesnaževanja in ukrepe za izboljšanje stanja. Osnovna cilja projekta INCOME sta razvoj integriranega sistema za podporo v odločanju (DSS) in predlog izvedljivega in sprejemljivega programa aktivnosti za podporo upravljanju z občutljivo ''urbano'' podzemno vodo v aluvialnih vodonosnikih pod visoko urbaniziranim področjem Mestne občine Ljubljana. ANG The INCOME project is intended for the establishment of an effective management of contaminated aquifers. The project connects procedures for discovering and supervising sources of pollution, and measures for improving the condition. The two primary objectives of the project are to develop an integrated decision making support system (DSS) and the proposal of a feasible/accepted program of activities for sustainable management of extremely vulnerable "urban" groundwater in the alluvial aquifer below the highly urbanized area of the Municipality of Ljubljana. Šifra D.01 Vodenje/koordiniranje (mednarodnih in domačih) projektov Objavljeno v JAMNIK, Brigita. Jasni ukrepi za dolgoročno izboljšanje stanja vodnih virov : evropski okoljevarstveni projekt INCOME. Ljubljana, oktober 2010, letn. 15, št. 7, str. 32. Tipologija 1.04 Strokovni članek COBISS.SI-ID 1866069 2. Naslov SLO Ustanovitev in postavitev raziskovalnega Laboratorija za tekočinskoscintilacijsko spektrometrijo ANG Establishment of low-level tritium laboratory Opis SLO Po tem, ko smo namestili opremo, smo analizirali zaporedje operacij, potrebnih za izvedbo analiznega postopka (vzorčevanje, konzerviranje vzorcev, prva destilacija, elektrolitska obogatitev, druga destilacija, priprava meritev in kontrolnih vzorcev, štetje in ocena rezultatov). Identificirali smo glavne vire negotovosti. Analitski proces smo preverili v nekaj mednarodnih primerjalnih meritvah in testih usposobljenosti. V prispevku predstavljamo rezultate in dileme, ki so se pojavile pri postavitvi laboratorija. ANG After installing the equipment the sequence of steps (sampling, conservation of samples, first distillation, electrolytical enrichment, second distillation, preparation of measurements and control samples, LSC counting, calculation and evaluation of the results) necessary to carry out the analytical procedure were analyzed. The main sources of uncertainties were identified. The analytical process was checked in several international intercomparisons and proficiency tests. The results and dilemmas that came up during the establishment of the laboratory are presented. Šifra D.02 Ustanovitev raziskovalnega centra, laboratorija, študija, društva Objavljeno v KOŽAR LOGAR, Jasmina, GLAVIC-CINDRO, Denis. Establishment of low-level tritium laboratory. V: EIKENBERG, Jost (ur.). LSC 2008, advances in liquid scintillation spectrometry : proceedings of the 2008 International Liquid Scintillation Conference, Davos, Switzerland, 25-30 May 2008. Tucson: Radiocarbon, 2009, str. 241-249. Tipologija 1.08 Objavljeni znanstveni prispevek na konferenci COBISS.SI-ID 22951207 3. Naslov SLO ANG Opis SLO ANG Šifra Objavljeno v Tipologija COBISS.SI-ID 4. Naslov SLO ANG Opis SLO ANG Šifra Objavljeno v Tipologija COBISS.SI-ID 5. Naslov SLO ANG Opis SLO ANG Šifra Objavljeno v Tipologija COBISS.SI-ID 8. Drugi pomembni rezultati projetne skupine8 Akreditacija pri Slovenski akreditaciji (LP-022, SIST EN ISO / IEC 17 025): Laboratorij za tekočinskoscintilacijsko spektrometrijo, (od 2008), Prva sistematična baza podatkov za tritij v slovenskih podzemnih vodah, kar je nujna in nepogrešljiva osnova za datiranje vod in določitev ranljivosti. Razvoj in vpeljava metod za določevanje drugih radionuklidov v vodah s tekočinskoscintilacijsko spektrometrijo: - meritve celokupnih sevalcev alfa in beta v vzorcih vode - določevanje Ra-226 in Ra-228 v vzorcih vode Dosežek bo objavljen v okviru diplomskih nalog Tine Vodopivec in Maruše Jerina. Metodi bosta vključeni v študij podzemnih vod. 9. Pomen raziskovalnih rezultatov projektne skupine9 9.1. Pomen za razvoj znanosti10 SLO Interpretacija merskih rezultatov v bližini detekcijske meje v spektrometriji gama še ni zadovoljivo rešena. V okviru projekta smo izpopolnili interpretacijo rezultatov s pomočjo Bayesianske statistike in z izdelavo empiričnega postopka, pri katerem lahko določimo verjetnosti za zmotno identifikacijo radionuklidov. Delo o sistematskih vplivih na rezultate v bližini detekcijske meje je v pripravi. Meritve Ra-226 pri nizkih koncentracijah predstavljajo poseben problem, zaradi časovno spremenljivega ozadja. Dve deli, ki obravnavata vire ozadja radonovih potomcev v spektrometrih gama, sta poslani v objavo. Izdelana metodologija je ustrezna za meritve pitnih vod skladno s priporočili Evropske komisije za vse sevalce gama. Za določitev geohidrokemijskih pogojev v vodonosnikih je treba metodologijo izpopolniti. Pokazalo se je, da so koncentracije torijevih izotopov, razen Th-228 pod detekcijsko mejo. Zato je potreba po novi merski tehniki s tekočinsko scintilacijsko spektrometrijo izotopov torija: tekočinskoscintilacijsko štetje alfa in beta po separaciji torija ter določanje koncentracij njegovih izotopov iz časovne odvisnosti obeh štetij. Izboljšava metode za določevanje vsebnosti tritija po elektrolitski obogatitvi bo omogočila natančnejše datiranje podzemnih vod širom po svetu. Zmanjšanje merskih negotovosti bodo ključenega pomena že v bližnji prihodnosti, saj si pri datiranju podzemnih vod ne bomo mogli več pomagati s tritijem, izpuščenim v ozračje med jedrskimi poskusi, ki smo ga zadnjih petdeset let uspešno uporabljali kot uro. Datiranje bo odvisno od tritija, ki v naravnih procesih nastaja v vrhnjih plasteh ozračja, ki pa ga je bistveno manj kot je bilo antropogenega »bombnega« tritija. Izboljšava metode je zato ključnega pomena. ANG_ The interpretation of measurement results in the vicinity of the detection limit in gamma-ray spectrometry is not satisfactory elaborated yet. In the framework of the project we have improved the interpretation of the results by use of the Bayesian statistics and by elaboration of an empirical procedure for determination of the probability for Type I errors in radionuclide detection. A manuscript dealing with systematic influences on results near the detection limit is in preparation. Measurements of Ra-226 near the detection limit present an additional problem because of the time variance of the spectrometer background. Two manuscripts, dealing with the radon-induced background of gamma-ray spectrometers, are sent for publication. The methodology elaborated suffices for drinking water measurements, complying with the recommendations of the European Commission for gamma-ray emitters. For the determination of hydrogeochemical conditions in aquifers the methodology has too be improved. The concentrations of thorium isotopes, except Th-228, are below the detection limit. For these isotopes a new measurement technique is required: liquid scintillation alpha and beta counting after thorium separation and determination of its isotopes from the time dependence of both count rates. Improvement of the method for determination of tritium content after electrolytic enrichment will enable more accurate dating of groundwater all over the world. Diminishing of measurement uncertainties will be of cruicial importance in very near future, because the amounts of tritium, released during bomb testing, practically are not detectable in the athmosphere and thereforcan't be used as a clock any more. Water age determination will be based on naturally produced tritium in the upper layers of the atmosphere, whith quantities, which are much smaller than were the quantities of antropogenic »bombing« tritium. The improvement of the method is therefore cruicial. 9.2. Pomen za razvoj Slovenije11 SLO_ V okviru projekta zbrani in izmerjeni podatki za slovenske podzemne vode so prvi te vrste. Sistematični nabor podatkov za vse pomembnejše vodonosnike je nujno potrebna osnova za kakršnokoli datiranje slovenskih podzemnih vod. Določitev starosti podzemnih vod je ključnega pomena za opredelitev ranljivosti vod in razumevanje dinamike v vodonosnikih, kar so nepogrešljivi podatki za sonaravno gospodarjenje z enim najpomembnejših strateških virov države. Naš prispevek je boljše poznavanje naravnega stanja slovenskih podzemnih vod, ki bo lahko v prihodnje tudi v pomoč strateškim odločitvam na področju opravljanja s pitnimi vodami. Poleg tega bomo podali tudi detajlno interpretacijo radionuklidov v podzemni vodi in v kakšnem obsegu so korelirani glede na ostale parametre vodonosnika. Opredelili bomo tudi njihov izvor, bodisi naraven ali antropogen. ANG This is the most comprehensive investigation of natural radioactivity of ground water in Slovenia till now. Systematic set of data for all most important aquifers is the indispensable basis for dating of slovenian groundwaters. Deteremination of groundwater age is cruicial for assesment of water vulnerability and sustainable management with one of the most important strategic source of the state. Our contribution is better understanding of the state of ground waters in Slovenia, which is aimed to support strategic decisions in the field of ground water management. In addition a detailed interpretation of radionuclide concentration in ground water will be given, relating with other parameters of the aquifers. 10. Samo za aplikativne projekte! Označite, katerega od navedenih ciljev ste si zastavili pri aplikativnem projektu, katere konkretne rezultate ste dosegli in v kakšni meri so doseženi rezultati uporabljeni Cilj F.01 Pridobitev novih praktičnih znanj, informacij in veščin Zastavljen cilj O DA O NE Rezultat d Uporaba rezultatov d F.02 Pridobitev novih znanstvenih spoznanj Zastavljen cilj .) DA O NE Rezultat d Uporaba rezultatov d F.03 Večja usposobljenost raziskovalno-razvojnega osebja Zastavljen cilj DA O NE Rezultat d Uporaba rezultatov d F.04 Dvig tehnološke ravni Zastavljen cilj O DA O NE Rezultat d Uporaba rezultatov d F.05 Sposobnost za začetek novega tehnološkega razvoja Zastavljen cilj O DA O NE Rezultat d Uporaba rezultatov d F.06 Razvoj novega izdelka Zastavljen cilj DA NE Rezultat d Uporaba rezultatov d F.07 Izboljšanje obstoječega izdelka Zastavljen cilj O DA O NE Rezultat d Uporaba rezultatov d F.08 Razvoj in izdelava prototipa Zastavljen cilj DA NE Rezultat d Uporaba rezultatov d F.09 Razvoj novega tehnološkega procesa oz. tehnologije Zastavljen cilj O DA O NE Rezultat d Uporaba rezultatov d F.10 Izboljšanje obstoječega tehnološkega procesa oz. tehnologije Zastavljen cilj O DA O NE Rezultat d Uporaba rezultatov d F.11 Razvoj nove storitve Zastavljen cilj .) DA O NE Rezultat d Uporaba rezultatov d F.12 Izboljšanje obstoječe storitve Zastavljen cilj O DA O NE Rezultat d Uporaba rezultatov d F.13 Razvoj novih proizvodnih metod in instrumentov oz. proizvodnih procesov Zastavljen cilj O DA O NE Rezultat d Uporaba rezultatov d F.14 Izboljšanje obstoječih proizvodnih metod in instrumentov oz. proizvodnih procesov Zastavljen cilj O DA O NE Rezultat d Uporaba rezultatov d F.15 Razvoj novega informacijskega sistema/podatkovnih baz Zastavljen cilj O DA O NE Rezultat d Uporaba rezultatov d F.16 Izboljšanje obstoječega informacijskega sistema/podatkovnih baz Zastavljen cilj O DA O NE Rezultat d Uporaba rezultatov d F.17 Prenos obstoječih tehnologij, znanj, metod in postopkov v prakso Zastavljen cilj .) DA O NE Rezultat d Uporaba rezultatov d F.18 Posredovanje novih znanj neposrednim uporabnikom (seminarji, forumi, konference) 1 Zastavljen cilj O DA O NE Rezultat d Uporaba rezultatov d F.19 Znanje, ki vodi k ustanovitvi novega podjetja ("spin off") Zastavljen cilj .> DA O NE Rezultat d Uporaba rezultatov d F.20 Ustanovitev novega podjetja ("spin off") Zastavljen cilj O DA O NE Rezultat d Uporaba rezultatov d F.21 Razvoj novih zdravstvenih/diagnostičnih metod/postopkov Zastavljen cilj O DA O NE Rezultat d Uporaba rezultatov d F.22 Izboljšanje obstoječih zdravstvenih/diagnostičnih metod/postopkov Zastavljen cilj O DA O NE Rezultat d Uporaba rezultatov d F.23 Razvoj novih sistemskih, normativnih, programskih in metodoloških rešitev Zastavljen cilj D DA O NE Rezultat d Uporaba rezultatov d F.24 Izboljšanje obstoječih sistemskih, normativnih, programskih in metodoloških rešitev Zastavljen cilj O DA O NE Rezultat d Uporaba rezultatov d F.25 Razvoj novih organizacijskih in upravljavskih rešitev Zastavljen cilj .> DA O NE Rezultat d Uporaba rezultatov d F.26 Izboljšanje obstoječih organizacijskih in upravljavskih rešitev Zastavljen cilj O DA O NE Rezultat d Uporaba rezultatov d F.27 Prispevek k ohranjanju/varovanje naravne in kulturne dediščine Zastavljen cilj O DA O NE Rezultat d Uporaba rezultatov .H F.28 Priprava/organizacija razstave Zastavljen cilj O DA O NE Rezultat d Uporaba rezultatov d F.29 Prispevek k razvoju nacionalne kulturne identitete Zastavljen cilj DA NE Rezultat d Uporaba rezultatov d F.30 Strokovna ocena stanja Zastavljen cilj .> DA O NE Rezultat d Uporaba rezultatov d F.31 Razvoj standardov Zastavljen cilj O DA O NE Rezultat d Uporaba rezultatov d F.32 Mednarodni patent Zastavljen cilj O DA O NE Rezultat d Uporaba rezultatov d F.33 Patent v Sloveniji Zastavljen cilj O DA O NE Rezultat d Uporaba rezultatov d F.34 Svetovalna dejavnost Zastavljen cilj D DA O NE Rezultat d Uporaba rezultatov d F.35 Drugo Zastavljen cilj O DA O NE Rezultat d Uporaba rezultatov d Komentar 11. Samo za aplikativne projekte! Označite potencialne vplive oziroma učinke vaših rezultatov na navedena področja Vpliv Ni vpliva Majhen vpliv Srednji vpliv Velik vpliv G.01 Razvoj visoko-šolskega izobraževanja G.01.01. Razvoj dodiplomskega izobraževanja O o o o G.01.02. Razvoj podiplomskega izobraževanja o o o o G.01.03. Drugo: o o o o G.02 Gospodarski razvoj G.02.01 Razširitev ponudbe novih izdelkov/storitev na trgu o o o o G.02.02. Širitev obstoječih trgov o o o o G.02.03. Znižanje stroškov proizvodnje o o o o G.02.04. Zmanjšanje porabe materialov in energije O O O O G.02.05. Razširitev področja dejavnosti o o o o G.02.06. Večja konkurenčna sposobnost o o o o G.02.07. Večji delež izvoza o o o o G.02.08. Povečanje dobička o o o o G.02.09. Nova delovna mesta o o o o G.02.10. Dvig izobrazbene strukture zaposlenih o o o o G.02.11. Nov investicijski zagon o o o o G.02.12. Drugo: o o o o G.03 Tehnološki razvoj G.03.01. Tehnološka razširitev/posodobitev dejavnosti O O O O G.03.02. Tehnološko prestrukturiranje dejavnosti o o o o G.03.03. Uvajanje novih tehnologij o o o o G.03.04. Drugo: o o o o G.04 Družbeni razvoj G.04.01 Dvig kvalitete življenja o o o o G.04.02. Izboljšanje vodenja in upravljanja o o o o G.04.03. Izboljšanje delovanja administracije in javne uprave O O O O G.04.04. Razvoj socialnih dejavnosti o o o o G.04.05. Razvoj civilne družbe o o o o G.04.06. Drugo: o o o o G.05. Ohranjanje in razvoj nacionalne naravne in kulturne dediščine in identitete O O O O G.06. Varovanje okolja in trajnostni razvoj O O O O G.07 Razvoj družbene infrastrukture G.07.01. Informacijsko-komunikacijska infrastruktura o o o o G.07.02. Prometna infrastruktura o o o o G.07.03. Energetska infrastruktura O o o o G.07.04. Drugo: o o o o G.08. Varovanje zdravja in razvoj zdravstvenega varstva O O O O G.09. Drugo: o o o o Komentar 12. Pomen raziskovanja za sofinancerje, navedene v 2. točki12 1. Sofinancer Vrednost sofinanciranja za celotno obdobje trajanja projekta je znašala: EUR Odstotek od utemeljenih stroškov projekta: % Najpomembnejši rezultati raziskovanja za sofinancerja Šifra 1. 2. 3. 4. 5. Komentar Ocena 2. Sofinancer Vrednost sofinanciranja za celotno obdobje trajanja projekta je znašala: EUR Odstotek od utemeljenih stroškov projekta: % Najpomembnejši rezultati raziskovanja za sofinancerja Šifra 1. 2. 3. 4. 5. Komentar Ocena 3. Sofinancer Vrednost sofinanciranja za celotno obdobje trajanja projekta je znašala: EUR Odstotek od utemeljenih stroškov projekta: % Najpomembnejši rezultati raziskovanja za sofinancerja Šifra 3. 4. 5. Komentar Ocena C. IZJAVE Podpisani izjavljam/o, da: • so vsi podatki, ki jih navajamo v poročilu, resnični in točni • se strinjamo z obdelavo podatkov v skladu z zakonodajo o varstvu osebnih podatkov za potrebe ocenjevanja, za objavo 6., 7. in 8. točke na spletni strani http://sicris.izum.si/ ter obdelavo teh podatkov za evidence ARRS • so vsi podatki v obrazcu v elektronski obliki identični podatkom v obrazcu v pisni obliki • so z vsebino zaključnega poročila seznanjeni in se strinjajo vsi soizvajalci projekta Podpisi: Matjaž Aleš Korun in podpis vodje raziskovalnega projekta zastopnik oz. pooblaščena oseba RO Kraj in datum: Ljubljana 19.4.2011 Oznaka poročila: ARRS-RPROJ-ZP-2011-1/57 1 Zaradi spremembe klasifikacije družbeno ekonomskih ciljev je potrebno v poročilu opredeliti družbeno ekonomski cilj po novi klasifikaciji. Nazaj 2 Samo za aplikativne projekte. Nazaj 3 Napišite kratko vsebinsko poročilo, kjer boste predstavili raziskovalno hipotezo in opis raziskovanja. Navedite ključne ugotovitve, znanstvena spoznanja ter rezultate in učinke raziskovalnega projekta. Največ 18.000 znakov vključno s presledki (približno tri strani, velikosti pisave 11). Nazaj 4 Realizacija raziskovalne hipoteze. Največ 3.000 znakov vključno s presledki (približno pol strani, velikosti pisave 11). Nazaj 5 V primeru bistvenih odstopanj in sprememb od predvidenega programa raziskovalnega projekta, kot je bil zapisan v predlogu raziskovalnega projekta oziroma v primeru sprememb, povečanja ali zmanjšanja sestave projektne skupine v zadnjem letu izvajanja projekta (obrazložitev). V primeru, da sprememb ni bilo, to navedite. Največ 6.000 znakov vključno s presledki (približno ena stran, velikosti pisave 11). Nazaj 6 Navedite največ pet najpomembnejših znanstvenih rezultatov projektne skupine, ki so nastali v času trajanja projekta v okviru raziskovalnega projekta, ki je predmet poročanja. Za vsak rezultat navedite naslov v slovenskem in angleškem jeziku (največ 150 znakov vključno s presledki), rezultat opišite (največ 600 znakov vključno s presledki) v slovenskem in angleškem jeziku, navedite, kje je objavljen (največ 500 znakov vključno s presledki), izberite ustrezno šifro tipa objave po Tipologiji dokumentov/del za vodenje bibliografij v sistemu COBISS ter napišite ustrezno COBISS.SI-ID številko bibliografske enote. Navedeni rezultati bodo objavljeni na spletni strani http://sicris.izum.si/. PRIMER (v slovenskem jeziku): Naslov: Regulacija delovanja beta-2 integrinskih receptorjev s katepsinom X; Opis: Cisteinske proteaze imajo pomembno vlogo pri nastanku in napredovanju raka. Zadnje študije kažejo njihovo povezanost s procesi celičnega signaliziranja in imunskega odziva. V tem znanstvenem članku smo prvi dokazali... (največ 600 znakov vključno s presledki) Objavljeno v: OBERMAJER, N., PREMZL, A., ZAVAŠNIK-BERGANT, T., TURK, B., KOS, J.. Carboxypeptidase cathepsin X mediates 62 - integrin dependent adhesion of differentiated U-937 cells. Exp. Cell Res., 2006, 312, 2515-2527, JCR IF (2005): 4.148 Tipopologija: 1.01 - Izvirni znanstveni članek COBISS.SI-ID: 1920113 Nazaj 7 Navedite največ pet najpomembnejših družbeno-ekonomsko relevantnih rezultatov projektne skupine, ki so nastali v času trajanja projekta v okviru raziskovalnega projekta, ki je predmet poročanja. Za vsak rezultat navedite naslov (največ 150 znakov vključno s presledki), rezultat opišite (največ 600 znakov vključno s presledki), izberite ustrezen rezultat, ki je v Šifrantu raziskovalnih rezultatov in učinkov (Glej: http://www.arrs.gov.si/sl/gradivo/sifranti/sif-razisk-rezult.asp), navedite, kje je rezultat objavljen (največ 500 znakov vključno s presledki), izberite ustrezno šifro tipa objave po Tipologiji dokumentov/del za vodenje bibliografij v sistemu COBISS ter napišite ustrezno COBISS.SI-ID številko bibliografske enote. Navedeni rezultati bodo objavljeni na spletni strani http://sicris.izum.si/. Nazaj 8 Navedite rezultate raziskovalnega projekta v primeru, da katerega od rezultatov ni mogoče navesti v točkah 6 in 7 (npr. ker se ga v sistemu COBISS ne vodi). Največ 2.000 znakov vključno s presledki. Nazaj 9 Pomen raziskovalnih rezultatov za razvoj znanosti in za razvoj Slovenije bo objavljen na spletni strani: http://sicris.izum.si/ za posamezen projekt, ki je predmet poročanja. Nazaj 10 Največ 4.000 znakov vključno s presledki Nazaj 11 Največ 4.000 znakov vključno s presledki Nazaj 12 Rubrike izpolnite/prepišite skladno z obrazcem "Izjava sofinancerja" (http://www.arrs.gov.si/sl/progproj/rproj/gradivo/), ki ga mora izpolniti sofinancer. Podpisan obrazec "Izjava sofinancerja" pridobi in hrani nosilna raziskovalna organizacija - izvajalka projekta. Nazaj Obrazec: ARRS-RPROJ-ZP/2011-1 v1.01 0C-D5-F9-4A-BC-7D-60-4B-7F-91-F9-3E-3C-03-03-9B-28-81-40-43 zap. št. kraj vzorčevanja datum vzorčenja vrsta vzorca x y 9 B-2 Brestovica 22.10.2008 11:47 vodnjak 74730 392755 10 B-3 Brestovica 22.10.2008 13:28 piezometer 74700 392400 8 B-9 Brestovica 21.10.2008 16:00 vodnjak 75106 392109 56 B-9 Brestovica 11.6.2009 14:41 vrtina 75106 392109 78 B-9 Brestovica 09.10.2009 16:00 vodnjak 75106 392109 22 BLP-2/04 15.4.2009 16:07 piezometer 162986 602609 32 BLP-2/04 13.5.2009 00:00 piezometer 162986 602609 121 BLP-2/04 28.4.2010 16:04 piezometer 162986 602609 61 Bočič 14.7.2009 10:57 izvir 131174,6 383899,6 73 Bočič 07.10.2009 11:34 izvir 131174,6 383899,6 125 Bohinjska Bistrica 09.6.2010 11:49 izvir 124151 417456 174 Bohinjska Bistrica 15.10.2010 12:15 izvir 124151 417456 62 Boka 14.7.2009 11:30 izvir 131727,6 384231,6 74 Boka 07.10.2009 12:01 izvir 131727,6 384231,6 42 C-4 Domžale 19.5.2009 09:34 vrtina 111465 467594 122 C-4 Domžale 29.4.2010 10:04 vrtina 111465 467594 127 Črna Logarska dolina 10.6.2010 12:23 izvir 140580 472369 168 Črna Logarska dolina 13.10.2010 12:28 izvir 140580 472369 49 DAC-3/98 26.5.2009 13:34 vodnjak 85100 541049 108 DAC-3/98 16.11.2009 17:15 piezometer 85100 541049 158 DAC-3/98 03.8.2010 10:12 piezometer 85100 541049 129 Debelčev mlin 10.6.2010 16:00 izvir 123199 472078 187 Debelčev mlin 15.11.2010 13:45 izvir 123199 472078 20 DEV-1 15.4.2009 11:20 vodnjak 150900 569790 101 DEV-1 12.11.2009 10:40 vodnjak 150900 569790 130 Dobličica 29.6.2010 11:46 izvir 45265 511576 179 Dobličica 28.10.2010 10:55 izvir 45265 511576 126 Dobravca 09.6.2010 13:48 izvir 136627 433366 166 Dobravca 12.10.2010 12:25 izvir 136627 433366 44 Dobrova-Jablance 19.5.2009 14:02 izvir 100633 535519 107 Dobrova-Jablance 16.11.2009 15:45 izvir 100633 535519 150 Framski slap 22.7.2010 11:32 zajetje 150827 542541 186 Framski slap 15.11.2010 11:15 izvir 150827 542541 64 Glijun 14.7.2009 13:00 izvir 133400 385700 76 Glijun 07.10.2009 14:05 izvir 133400 385700 149 Gornji Ig 21.7.2010 14:42 izvir 86400 461000 177 Gornji Ig 27.10.2010 12:30 izvir 86400 461000 37 Gornji Lakoš 14.5.2009 15:08 vodnjak 157701 608756 134 Grad Snežnik 30.6.2010 13:42 izvir 59911 459004 189 Grad Snežnik 15.11.2010 10:45 izvir 59911 459004 34 Grad-1/02 13.5.2009 13:14 vrtina 184938 583441 119 Grad-1/02 28.4.2010 11:44 vrtina 184938 583441 151 Gradišče 22.7.2010 13:29 zajeti izvir 167521 584972 171 Gradišče 14.10.2010 13:30 zajeti izvir 167521 584972 143 Grajsko zajetje 15.7.2010 10:29 izvir 102738 446793 188 Grajsko zajetje 15.11.2010 15:25 izvir 102738 446793 45 Grešnikov hrib 20.5.2009 10:19 izvir 99250 473230 118 Grešnikov hrib 07.12.2009 14:05 izvir 99250 473230 29 Hotešk 12.5.2009 13:01 izvir 110160 406612 94 Hotešk 28.10.2009 11:28 izvir 110160 406612 27 Hubelj 11.5.2009 13:43 izvir 85022 416048 95 Hubelj 28.10.2009 13:15 izvir 85022 416048 58 Ilirska Bistrica 16.6.2009 10:49 izvir 47345 441976 97 Ilirska Bistrica 29.10.2009 10:00 izvir 47345 441976 144 Iščica 15.7.2010 12:13 izvir 90597 463736 184 Iščica 29.10.2010 12:17 izvir 90597 463736 137 Izvir Soče 12.7.2010 16:36 izvir 141700 402200 175 Izvir Soče 15.10.2010 14:15 izvir 141700 402200 23 Jelševa Loka 16.4.2009 11:18 izvir 136200 522000 89 Jelševa Loka 27.10.2009 11:30 izvir 136200 522000 48 Jurčičev izvir 25.5.2009 16:19 izvir 111215 454084 123 Jurčičev izvir 29.4.2010 12:14 izvir 111215 454084 68 Kamniška Bistrica 15.7.2009 14:30 izvir 131580 468815 88 Kamniška Bistrica 21.10.2009 15:30 izvir 131580 468815 153 Kamniška Bistrica 27.7.2010 08:20 izvir 131580 468815 14 Kleče 24.2.2009 09:40 lizimeter 65 Krajcarica 14.7.2009 16:30 izvir 138350 406100 77 Krajcarica 07.10.2009 15:32 izvir 138350 406100 18 Krka 09.4.2009 13:55 izvir 82860 482630 109 Krka 17.11.2009 10:30 izvir 82860 482630 154 Krka 27.7.2010 09:50 izvir 82860 482630 69 Kropa 15.7.2009 16:00 izvir 127445 487875 92 Kropa 27.10.2009 16:40 izvir 127445 487875 15 Krupa 08.4.2009 13:36 izvir 54532 517307 114 Krupa 18.11.2009 14:03 izvir 54532 517307 157 Krupa 02.8.2010 11:45 izvir 54532 517307 66 Lipnica 14.7.2009 18:45 izvir 131090 435700 87 Lipnica 21.10.2009 13:50 izvir 131090 435700 145 Lipnik 20.7.2010 10:25 izvir 138300 425500 165 Lipnik 12.10.2010 11:30 izvir 138300 425500 38 Lipovci 2271 14.5.2009 16:48 vrtina 165177 594133 25 LMP-1/06 06.5.2009 14:18 vrtina 103755 461963 124 LMP-1/06 29.4.2010 13:04 vodnjak 103755 461963 128 Lučnica 10.6.2010 13:43 izvir 129972 477111 167 Lučnica 13.10.2010 10:30 izvir 129972 477111 11 Mahniči 19.11.2008 12:00 izvir 71156 415345 30 Malenščica 12.5.2009 15:27 izvir 75609 442532 116 Malenščica 07.12.2009 11:30 izvir 75609 442532 140 Mazej 13.7.2010 14:29 izvir 141328 500219 169 Mazej 13.10.2010 13:48 izvir 141328 500219 131 Metliški Obrh 29.6.2010 13:05 izvir 56485 525155 180 Metliški Obrh 28.10.2010 11:20 izvir 56485 525155 3 Miren 0330 13.10.2008 15:34 vodnjak 84800 392520 52 Miren 0330 02.6.2009 16:12 vodnjak 84800 392520 81 Miren 0330 19.10.2009 17:25 vodnjak 84800 392520 43 Mitovšek 19.5.2009 12:10 izvir 108450 502720 112 Mitovšek 18.11.2009 10:23 izvir 108450 502720 31 Močilnik 12.5.2009 16:57 izvir 90240 445550 117 Močilnik 07.12.2009 13:10 izvir 90240 445550 146 Mošenik 20.7.2010 13:28 izvir 142100 444273 164 Mošenik 12.10.2010 09:10 izvir 142100 444273 135 Mrzlek 12.7.2010 10:43 izvir 95415 395150 172 Mrzlek 15.10.2010 10:20 izvir 95415 395150 4 NG-4/75 14.10.2008 13:30 piezometer 84377 391735 50 NG-4/75 02.6.2009 12:37 vrtina 84377 391735 82 NG-4/75 20.10.2009 12:02 vrtina 84377 391735 60 O-1/91 18.6.2009 14:04 vrtina 48273 410870 80 O-1/91 19.10.2009 14:15 vrtina 48273 410870 141 Obrh Rinža 14.7.2010 10:50 izvir 58000 486700 190 Obrh Rinža 25.11.2010 10:00 izvir 58000 486700 59 Odolina 16.6.2009 12:09 izvir 50062 423852 98 Odolina 29.10.2009 11:05 izvir 50062 423852 1 Orehovlje 0420 13.10.2008 12:00 vodnjak 83546 392740 51 Orehovlje 0420 02.6.2009 14:17 vodnjak 83546 392740 83 Orehovlje 0420 20.10.2009 15:03 vodnjak 83546 392740 40 OV-29 18.5.2009 15:32 hišni vodnji 143716 556716 103 OV-29 12.11.2009 14:50 hišni vodnja 143716 556716 161 OV-29 12.8.2010 14:30 hišni vodnja 143716 556716 142 Padiščak 14.7.2010 14:03 izvir 39614 397009 185 Padiščak 15.11.2010 13:15 izvir 39614 397009 72 Pasji rep 22.7.2009 10:00 izvir 71535 420148 100 Pasji rep 29.10.2009 14:00 izvir 71535 420148 6 Pliskovica P-1 21.10.2008 11:00 vrtina 69843 405820 28 Podroteja 11.5.2009 15:08 izvir 94000 425180 93 Podroteja 28.10.2009 10:10 izvir 94000 425180 133 Podturn 30.6.2010 11:30 izvir 66422 503457 191 Podturn 25.11.2010 11:40 izvir 66422 503457 46 Potok pri dvorcu Visoko 20.5.2009 13:09 površinski v 109652 438992 105 Potok pri dvorcu Visoko 13.11.2009 10:50 površinski v 109652 438992 147 Pšata 20.7.2010 14:38 izvir 124201 462272 183 Pšata 29.10.2010 10:15 izvir 124201 462272 19 Rakitnica 10.4.2009 11:00 izvir 61215 480436 110 Rakitnica 17.11.2009 12:15 izvir 61215 480436 39 Rankovci 3370 18.5.2009 13:52 vrtina 170605 583057 53 Rižana 03.6.2009 11:24 izvir 43209 413333 99 Rižana 29.10.2009 12:30 izvir 43209 413333 156 Rižana 27.7.2010 11:42 izvir 43209 413333 12 Rv-2/90 19.11.2008 12:00 vrtina 71140 415325 57 Rv-2/90 15.6.2009 11:40 vrtina 71140 415325 79 Rv-2/90 15.10.2009 10:55 vrtina 71140 415325 13 Rv-3/90 19.11.2008 12:00 vrtina 69962 416358 67 Savica 15.7.2009 10:20 izvir 128350 407330 86 Savica 21.10.2009 11:45 izvir 128350 407330 160 Savica 12.8.2010 10:25 izvir 128350 407330 139 Skorba 13.7.2010 12:41 vrtina 141953 563379 170 Skorba 14.10.2010 11:31 vrtina 141953 563379 16 Ščetar 08.4.2009 16:16 izvir 87015 523032 113 Ščetar 18.11.2009 12:10 izvir 87015 523032 5 ŠE-1/94 16.10.2008 12:00 vrtina 87285 394310 55 ŠE-1/94 03.6.2009 17:47 vrtina 87285 394310 85 ŠE-1/94 20.10.2009 18:02 vrtina 87285 394310 54 Šempeter 0220 03.6.2009 16:17 vrtina 87520 394940 84 Šempeter 0220 20.10.2009 16:37 vodnjak 87520 394940 2 Šempeter 0840 13.10.2008 14:08 hišni vodnja 123490 510688 41 Šempeter 0840 18.5.2009 17:48 hišni vodnja 123490 510688 115 Šempeter 0840 19.11.2009 14:30 hišni vodnja 123490 510688 159 Šempeter 0840 03.8.2010 16:03 hišni vodnja 123490 510688 71 Šumec 1 16.7.2009 15:20 izvir 152600 487310 91 Šumec 1 27.10.2009 14:40 izvir 152600 487310 132 Težka voda 29.6.2010 14:50 izvir 69141 516536 181 Težka voda 28.10.2010 13:40 izvir 69141 516536 17 Tominčev izvir 09.4.2009 00:00 izvir 72369 498020 111 Tominčev izvir 17.11.2009 13:55 izvir 72369 498020 47 Trebija 20.5.2009 14:19 izvir 106590 430333 104 Trebija 13.11.2009 10:10 izvir 106590 430333 7 VB-4/80, črpališče Klariči 21.10.2008 14:17 vodnjak 75343 391455 24 Velika Toplica 16.4.2009 13:17 izvir 128320 545040 106 Velika Toplica 16.11.2009 12:20 izvir 128320 545040 36 Veščica 0120 14.5.2009 13:42 vrtina 154648 596753 148 VG-10 Mala Goba 21.7.2010 10:27 vrtina 99601 498990 178 VG-10 Mala Goba 27.10.2010 14:55 vrtina 99601 498990 26 Vipava 11.5.2009 12:29 izvir 78321 419945 96 Vipava 28.10.2009 14:25 izvir 78321 419945 155 Vipava 27.7.2010 13:00 izvir 78321 419945 152 Vodice Vo-1 23.7.2010 08:14 vrtina 116160 462653 182 Vodice Vo-1 29.10.2010 09:25 vrtina 116160 462653 33 VP-1/2000 13.5.2009 00:00 vrtina 178100 600250 120 VP-1/2000 28.4.2010 13:24 vrtina 178100 600250 138 Vt-1 Tinsko 13.7.2010 11:03 vrtina 113876 541943 176 Vt-1 Tinsko 27.10.2010 09:40 vrtina 113876 541943 35 Vučja vas 14.5.2009 10:34 vrtina 162220 584566 21 Vurberk 15.4.2009 12:57 izvir 149665 562240 102 Vurberk 12.11.2009 12:25 izvir 149665 562240 136 Zadlaščica 12.7.2010 14:15 izvir 121490 406210 173 Zadlaščica 15.10.2010 12:12 izvir 121490 406210 70 Žegnan studenec 16.7.2009 12:52 izvir 149185 518038 90 Žegnan studenec 27.10.2009 12:50 izvir 149185 518038 63 Žvika 14.7.2009 12:09 izvir 131956 384853,6 75 Žvika 07.10.2009 12:28 izvir 131956 384853,6 162 24.6.2010 12:00 deževnica 163 09.8.2010 12:00 deževnica 36 41 22 22 22 158 158 158 351 351 77,6 77,6 305 305 464 464 464 255 255 461 410 410 435 435 165 271 271 335 335 190 3H 474 743 632 553 673 1108 1208 1035 735 566 702 A 3H MDC 210 Pb A 210Pb 228 Th A 228Th 100 130 85 73 95 147 110 101 47 79 58 15,78 13,66 8,78 0,87 1,35 0,72 0,10 0,33 0,05 0,13 793 856 0 527 705 144 80 35 44 51 58 4,91 0,52 0,10 0,07 967 942 99 82 5,02 3,69 0,90 0,99 622 47 149 117 49 14 3,61 5,93 0,58 0,71 0,82 0,09 699 53 855 628 78 55 4,39 4,30 0,79 0,61 813 707 64 54 1,26 3,80 0,26 0,62 0,26 0,07 524 79 91 171 18 18 4,71 0,67 690 851 585 98 187 86 8,62 2,18 0,89 0,50 0,41 0,40 190 800 65 1,13 0,38 9,80 225 661 79 2,62 0,55 4,01 225 891 77 2,90 0,43 4,08 420 262 50 3,82 0,40 0,06 0,05 6,02 420 544 49 2,63 0,47 5,88 420 787 101 2,44 0,62 0,10 0,08 12,78 420 719 59 10,24 1,33 15,05 327 590 59 1,56 0,75 19,81 327 742 58 600 869 62 0,98 0,24 0,08 0,05 2,19 600 715 65 1,38 0,38 1,65 600 867 78 690 982 58 1,83 0,39 2,37 690 697 84 0,00 0,73 2,76 270 665 65 4,78 0,50 0,26 0,07 26,27 270 209 31 3,41 0,58 33,17 270 406 739 62 4,07 0,40 0,10 0,05 6,26 406 742 91 1,96 0,48 7,02 136 849 130 32,75 2,04 14,46 136 867 85 7,65 0,87 24,46 136 492 762 120 1,09 0,33 0,23 0,07 5,24 492 721 52 2,97 0,42 5,52 181 876 79 9,74 1,05 57,94 314 740 78 5,03 0,65 0,08 0,07 16,87 314 826 57 603 44 255 958 129 459 695 75 3,66 0,47 0,03 0,06 9,64 459 664 65 5,43 0,68 9,19 55 655 93 55 406 73 1,34 0,42 0,09 0,06 47,47 55 732 81 1,97 0,75 61,32 270 705 178 2,92 0,42 0,11 0,05 7,89 270 591 60 3,98 0,58 8,75 290 748 69 3,86 0,32 0,13 0,04 13,66 290 676 54 6,55 0,71 23,60 44 44 44 27 27 509 509 50 50 50 244 244 244 227 227 202 327 327 755 755 453 453 198 72 72 72 251 251 251 273 840 840 840 184 184 68 68 68 35 56 67 29 56 92 4,07 2,77 0,67 0,68 0,09 0,07 27,78 26,80 97 114 109 78 53 76 164 1,92 1,19 12,48 13,31 0,36 0,37 1,64 1,23 0,14 0,09 25,97 11,25 307,90 280,10 86 68 135 62 72 1,27 1,00 6,29 4,66 0,41 0,43 0,59 0,59 0,13 0,04 3.40 42,94 6,91 7.41 61 65 2,38 1,15 0,58 0,40 16,86 16,72 55 65 81 99 70 9,55 3,97 21,38 2,44 4,64 0,58 0,51 1,53 0,38 0,64 0,10 0,12 0,05 0,05 7,95 7,22 43,23 12,19 15,77 109 33 57 87 70 76 4,92 3,46 0,47 1,04 0,59 0,61 0,27 0,48 0,13 0,10 0,08 16,77 15,86 0,06 1,53 0,00 87 56 33 96 38 52 4,38 0,43 0,36 0,06 16,95 6,16 0,77 17,94 69 632 57 69 419 55 272 631 63 272 1066 97 17,69 1,42 31,60 272 15,92 1,19 30,15 272 665 1178 85 1,15 0,26 0,22 0,05 4,50 665 1111 88 2,48 0,47 3,80 222 680 67 13,29 0,80 0,34 0,08 10,92 222 831 60 4,44 0,70 14,85 470 668 129 4,29 0,74 9,11 470 769 75 2,63 0,43 8,04 23 670 126 284 829 109 4,21 0,57 0,06 0,06 5,84 284 653 123 1,33 0,53 5,79 172 708 86 100 592 70 4,98 0,70 9,94 100 764 68 5,23 0,55 8,06 100 250 4,81 0,64 21,26 250 58 11 228 75 342 1189 121 2,46 0,53 0,20 0,06 19,77 342 1400 131 4,28 0,58 16,46 1490 749 47 7,42 0,50 0,10 0,05 19,48 1490 860 126 12,26 0,98 15,58 385 700 60 385 508 47 A 40K 228Ra A 228Ra 238U A 238U 226Ra A 226Ra 2,06 0,88 0,17 6,50 0,57 2,44 0,28 2,69 3,49 3,05 0,23 5,29 0,14 3,39 0,31 2,52 0,24 0,15 5,12 0,36 0,41 0,13 2,45 5,09 0,25 16,89 1,68 3,55 0,25 3,01 2,81 2,98 0,63 1,16 0,06 0,10 0,23 0,10 3,73 1,44 1,85 0,16 2,61 0,32 16,15 0,92 1,99 1,53 1,55 1,33 1,12 0,97 1,60 0,44 0,17 5,29 0,14 1,11 0,15 1.45 0,81 0,23 4,36 0,17 1,22 0,17 2.46 2,67 0,70 0,49 0,18 0,54 0,15 1,13 1,06 1,07 2,25 3,90 0,86 0,19 4,88 0,62 0,96 0,14 0,96 1,71 2,49 2,89 0,63 0,19 0,16 0,15 0,99 1,08 0,62 0,28 0,23 0,12 6,39 1,58 0,59 0,18 11,11 0,28 1,16 0,48 0,18 4,28 0,49 1,09 0,17 1,64 3,59 6,57 0,95 1,73 1,20 2,76 0,79 0,55 0,60 0,14 0,12 5,32 1,24 0,34 0,50 0,07 0,19 0,12 4,21 0,07 0,68 0,11 0,12 0,09 2,49 0,73 0,31 0,24 0,20 3,43 2,19 0,75 1,61 0,17 3,60 0,15 0,74 0,14 32,28 28,67 0,93 4,60 0,20 0,11 0,19 0,10 1,23 1,53 2,20 2,09 1,11 1,33 4,97 1,28 2,07 0,61 0,17 4,54 0,29 1,15 0,13 0,67 0,14 0,81 0,15 1,86 0,83 2,68 0,20 10,73 0,55 2,37 0,30 0,75 0,27 0,17 2,35 0,23 0,11 0,94 1,30 0,15 3,71 3,29 3,39 0,31 2,42 4,02 3,34 0,94 1,69 0,65 0,12 2,29 0,25 1,27 2,04 1,70 1,38 0,71 0,25 5,13 0,83 1,56 0,20 1,19 1,37 0,72 0,17 3,17 0,16 4,84 0,38 2,83 1,86 1,03 0,13 13,47 0,32 0,81 0,12 2,13 2,47 0,59 0,20 0,18 0,09 2,07 Background of radon daughters in gamma-ray spectrometric measurements P. Maver Modec1*, M. Korun1, M. Martelanc2, B. Vodenik1 Jožef Stefan Institute, Jamova cesta 39, Ljubljana, Slovenia ^Faculty of Computer and Information Science, Tržaška cesta 25, Ljubljana, Slovenia Abstract: An analysis of radon-induced background on nine high-resolution gamma-ray spectrometers is presented. The contributions of the detector contamination, contamination of air inside the shield cavity and the radiation penetrating the detector shield are evaluated. Whereas the detector contamination and the radiation penetrating the shield are constant in time, the contamination of air varies due to variation of the outdoor temperature. The data extracted from the analysis are used for calculation of the background count rates during sample measurements and the count rates in peaks too weak to be measured directly. Introduction. When samples from the environment are measured on gamma-ray spectrometers 226Ra can be determined either from its peak occurring at the energy 186 keV or from the concentrations of radon daughters in the sample. The later method has * Corresponding author: Petra Maver Modec, tel.: +386 1 4773900, fax: +386 1 4773151, e-mail: petra.maver@ij s.si 214 214 the advantage that it is more sensitive. Radon daughters Pb and Bi radiate at several energies with the probability which is much larger than the probability for emission of the gamma-rays in the decay of 226Ra. Unfortunately, the activity of 226Ra in the sample is small a substantial part of the areas of peaks signaling the presence of radon daughters in the sample may originate in the spectrometer background. To arrive at an unbiased result the peak areas must be corrected for the background contribution. Therefore background measurements are performed, which are used to determine the count rates in the peaks occurring in the spectra in the absence of the sample. Radon daughters in the spectrometer background originate in the presence of 226Ra in the detector, the shielding, the materials surrounding the shielding where the rays penetrating the shield originate, and in the presence of radon and its daughters in the air filling the shield's cavity. Whereas the contribution from contamination from detector, shielding and the environment is constant in time, the contribution due to radon contamination in the air may vary. Therefore the count rate in the background peaks due to radon daughters may vary with time and can be not determined as a simple average over the count rates in repeated background measurements. It is the purpose of this contribution to present an analysis of the radon-induced background and the sources of background due to radon daughters in the spectrometers of the Laboratory for Radiological Measuring Systems and Radioactivity Measurements at the Jožef Stefan. Materials and Methods The counting room is located in the basement, below the ground level. It is kept at a constant temperature. It is not ventilated to avoid possible contamination, the air is exchanged only by the draught. The draught is stronger at low outside temperatures since then the cooler air from the ambient tends to replace the warmer air in the counting room. During summer, in the counting room radon concentration may reach 600 Bq/m3 in winter the average concentration is 70 Bq/m3. The counting room houses nine spectrometers with high-energy germanium detectors of various properties. The characteristics of the detector shields are given in Table 1. The graded layers to prevent registration of X-rays are omitted from the table because of clearness. The shield cavities, except the cavity f the detector PO, are flushed constantly with nitrogen in order to replace ambient air, contaminated with radon, from the interior of the shield. The nitrogen is obtained by evaporation of liquid nitrogen, aged for two weeks to allow radon to decay. Because of the limited supply of nitrogen, some shields are not flushed completely, therefore some contamination of radon daughters remains within the cavity. This is reflected in seasonal variations of the background of radon daughters in some spectrometers, which occurs in spite of flushing. The seasonal variations of the cunt rate in the peak at 352 keV in the background measurements on the spectrometer MG, having the largest shield cavity, are presented in Fig. 1. On Fig. 2 this peak count rate is presented as a function of the outside temperature, averaged over the counting time of the measurement. Background measurements are performed at times when samples for activity measurements are not available. The acquisition time of background measurement is between 3 days and 12 days. Besides other peaks, occurring in the background spectrum, the count rate in the peaks of radon daughters is determined from the measured spectra. Some of the peaks are not identified in all background measurements because of poor statistics or poor deconvolution of multiplets when statistical uncertainties of peak areas are high. Here we analyze only the count rates at energies, where peaks are recognized in a great majority of measurements. These peaks occur at energies 75 keV, 77 keV, 87 keV, 242 keV, 295 keV, 352 keV, 609 keV, 768 keV, 1120 keV, 1238 keV, 1765 keV, 2204 keV and 2447 keV. Some of these energies are omitted from the data on spectrometers whre the peaks are not recognized in background measurements frequently enough. Results It can be observed on Fig. 1 that count rates in background peaks may be subject to seasonal variations. Below a critical outside temperature the count rate does not depend on the outside temperature, since then the radon concentration is low enough that the flushing effectively removes all radon from the shield cavity. The effectiveness of flushing depends on the volume of the air in the cavity, intensity of flushing and the permeability of the shield for air. On the detectors, which exhibit the temperature dependence, this critical temperature varies between 14 °C and 20 °C. The count rate below the critical temperature is determined, besides by the detector efficiency, by the contamination of the detector and shield with 226Ra and by the penetration rate of gamma-rays from the counting room through the shield. Above the critical temperature the count rate increases linearly with the outside temperature. The rate at which it increases depends on the effectiveness of flushing, the volume of the shield cavity and the detector efficiency. During the background measurements the detector measures the flux of gamma-rays at the center of the shield's cavity, where it is placed. To convert count rates into activities, characterizing contaminations, the response of the detector and the probability for emission of gamma-rays has to be taken into account. To assess the contamination, apparent activities A(E) are calculated as n( E) A( E) E )b( E) where n(E) denotes the count rate in the peak at the energy E, n(E) the counting efficiency of a source, positioned at the detector surface on the symmetry axis of the detector cap, radiating gamma-rays with the energy E, and b(E) the probability for emission of gamma-rays with the energy E in a decay of a radon daughter. It should be noted that the point-source efficiency only poorly represents the average probability for registration of a gamma-ray impinging under large angle on the detector cap, since it describes the probability for registration of a photon emitted isotropically from the point source. Although the point-source efficiency used is maximal, it underestimates the average probability. Therefore apparent activities overestimate flux rates, normalized to the emission probability of unity. The Fig. 3 presents apparent activities, corresponding to count rates in the spectrum below the critical temperature, for the spectrometers installed in the counting room. Discussion It can be observed that in the energy range above 500 keV the apparent activity increases with energy in almost all spectrometers. In general, the apparent activity is an increasing function of energy. This is due to the decreasing attenuation coefficient for photons in the shielding material. The rate of increasing bears the information on the thickness of the material between the contamination and the detector. Below 500 keV the photons can't penetrate the layers of the shielding, therefore here the apparent activity indicates the contamination of the detector and inner surface of the cavity with 226Ra. The increase of the apparent activities over this level indicates contributions from the shield material and from the exterior of the shield. The count rate in the X-ray peaks is difficult to interpret in terms of the apparent activity because of the X-ray fluorescence of lead, which interferes with the X-ray lines from 214Bi, which belong to the decay of radon daughters. Namely, the graded layers (made of cadmium and copper) do not attenuate the fluorescence completely. In addition to that, deconvolution of multiplets is not reliable at large statistical uncertainties of peak areas. Therefore apparent activities at energies which coincide with the energy of lead X-rays (75 keV and 87 keV) are given only in cases where no lead is used in the shielding, or where the inner layer absorbs the fluorescent X-rays completely and where the decomposition of multiplets is reliable enough. It can be seen on the Fig. 3 that apparent activities calculated from X-ray peak reproduce roughly the apparent activities due to the detector contamination except on the detector FE, where the increased activity indicates presence of lead within the detector. The flux of gamma-rays at the outer surface of the inner layer, AO(E), can be calculated from the increase of the apparent activity over its value, due to the contamination of the detector and the inner surface, and corrected for the attenuation of the gamma-rays in the inner layer. It is calculated as AO( E) = (A( E) -AD)eMl(E )d'p' where ^i(E), di and pI denote the attenuation coefficient, the thickness and the density of the material of the inner layer respectively. AD denotes the apparent activity due to the contamination of the detector and the shield and is given by the apparent activity averaged in the energy range between 200 keV and 400 keV. This calculation can be performed for all detectors except for the detector RA, where the thickness of the shield is not well defined. The apparent activities AO(E) are presented on Fig. 4. An apparent activity, increasing with energy, indicates penetration of gamma-rays through the outer layer. On the other hand, an apparent activity, decreasing with energy, indicates contamination of the inner layer or an effective shield thickness smaller than the nominal thickness, indicating presence of ducts. An activity, independent on energy, indicates the contamination at the outer surface of the inner layer. The effective thickness of the shield of the spectrometer RA can be assessed from the increase of the apparent activity over its value, AD. The assessment is done relative to the apparent activity at the lowest energy, where a substantial increase over AD is observed, i.e. at 609 keV: ln A( E) - Ad d (E) = A (609 keV) - Ad . [^(609 keV) E )]p The effective thickness, calculated as a function of energy is presented in Table 2. A slight increase in the average value indicates additional attenuation outside the shield, i.e. in the material, where the gamma-rays are emitted. The energy dependence of AO(E) indicates presence of ducts in the spectrometers PB, MO and PO. The effective shield's thickness of these spectrometers can be assessed analogously to the spectrometer RA and amount (1.9 ± 0.2) cm, (5.3 ±0.3) cm and (3.9 ± 0.4) cm respectively. The small effective thickness for the spectrometer PB points to an important duct, what can be observed already in the Fig. 3. Here an increase of the apparent activity at the energy of 352 keV is visible. The spectrometers FE, MG and HG do not have ducts, whereas the increasing energy dependence in the spectrometers SE and BL at the boundary between the inner and outer layer indicate the necessity of of the additional outer layer of the shield. The detector HG exhibits only slight contamination of the detector and/or contamination of the graded layers preventing registration of fluorescence from the shield. The time dependence of the radon-induced background originates in the variable concentration of radon in the ambient air, which affects the contamination of air within the cavity by the draught through the spectrometer. Variations due to draught were observed on the detectors PO, MG, BL and RA. The critical outdoor temperatures, where the background starts to rise are 15 °C, 14 °C, 20 °C and 18 °C respectively. The largest effect relative to the background below the critical temperature is observed at the energy of 295 keV. The increase of the background at outdoor temperatures exceeding the critical level we describe empirically with a linear function with a slope extracted from the background measurements. In table 3 the slopes for different detectors and different energies are given at energies where calculated slopes differ significantly from zero. It can be observed that the strongest temperature dependence exhibits the spectrometer with the largest cavity with a shield of lead bricks having rifts between bricks. The second largest dependence occurs in the spectrometer where no flushing is performed. These two spectrometers exhibit also the lowest critical temperature. In the spectrometer MG an increase of the slope with energy is observed. This is due to the diffusion of radon into the paraffin layer and the stronger attenuation of gamma-rays in the paraffin at lower energies. It should be noted that the increase of the background relative to that below the critical temperature may easily reach 100%. Therefore it is of vital importance to take it into account, especially when measuring concentrations of 238U and 226Ra in low-activity samples such as dry residue, obtained after evaporation of water, aerosol filters and water filters of suspended particulates, as described by Korun and Kovačič, 2010. In routine measurements the time-dependence of the background is taken into account via the measurement of the outdoor temperature. Daily averages of the outdoor temperature are recorded and the background count rates during the measurement time are calculated. These count rates are used for correction of peak count rates in the peaks in the spectra. Here the possible lag of the count rates behind the outdoor temperature is neglected. Conclusion For nine spectrometers mounted in the counting room of the Laboratory for Radiological Measuring Systems and Radioactivity Measurements the sources of radon-induced background have been determined. The contributions due to the contamination of the detector, the time-dependent air contamination in the shield cavity and the radiation penetrating the shields were calculated. These data are used for calculation of the radon background during the sample measurement and the calculation of background count rates in peaks, which are to weak to be analyzed reliably. Therefore by the analysis presented the results of routine measurements were improved, especially in measurements of low-activity samples. References Korun, M., Kovačič, K., 2010. 238U determination in ground water samples by gamma-ray spectrometry, submitted for publication to Appl. Radiat. Isot. Table 1 Characteristics of the detector shields Spectrometer Inner layer Outer layer Volume of code Material Thickness cm Material Thickness the shield cavity L FE iron 15 32 PB lead 16 5 MO Lead 12 5 PO Lead 10 2 MG Paraffin 10 Lead 12 34 SE Mercury 1 Lead 10 17 HG Mercury 1 Lead 12 11 BL Mercury 1 Lead 10 14 RA Lead 3 - 5 16 Table 2. The effective thickness of the shield for the spectrometer RA calculated at energies exceeding 609 keV Energy [keV] Effective thickness [cm] 768 4.0 ± 0.9 1120 3.8 ± 0.5 1238 3.9 ± 0.5 1764 4.3 ± 0.6 2204 4.6 ±0.6 2247 4.7 ± 0.7 Table 3. The coefficients of the temperature dependence of the background count rate Temperature dependence of the count rate / s-1°C-1 Detector PO MG BL RA Critical 15 14 20 18 temperature °C Energy keV 75 0.015 ± 0.003 77 0.010 ± 0.003 0.017 ± 0.003 0.013 ± 0.014 87 0.005 ± 0.002 0.010 ± 0.003 295 0.011 ± 0.02 0.039 ± 0.004 0.029 ± 0.015 0.0020 ± 0.0006 352 0.010 ± 0.002 0.038 ± 0.004 0.031 ± 0.019 0.0019 ± 0.0006 609 0.011 ± 0.002 0.042 ± 0.005 0.020 ±0.006 0.0019 ± 0.0007 768 0.042 ± 0.005 1120 0.010±0.003 0.045 ± 0.004 0.036 ± 0.025 0.0007 ±0.0004 1238 0.015 ± 0.008 0.050 ± 0.005 1764 0.015 ± 0.004 0.055 ± 0.005 0.028 ± 0.023 2204 0.060 ± 0.007 Figure captions Fig. 1 Seasonal variations of the count rate of the peak at 352 keV in background measurements on the spectrometer MG Fig. 2. The temperature dependence of the count rate in the peak at 352 keV in the background measurements on the spectrometer MG Fig. 3. The energy dependence of the apparent activities for nine spectrometers Fig. 4. The energy dependence of the apparent activities AO(E) Figure 1 0.02 0.018 ^ 0.016 - - - H - -- ' - 1 0.014 ^^ 0.012 " (U o k> o o o o o o o 3 D D □ 3 IH 00 X o H H o o k> o -3 cn m o o k) o O 0 01 o o "D O o o "D o o "D 00 -D D m Fig. 4 400 200 100 100 ^ 100 F o < 0 I- 0.4 0.2 0.0 0.2 0.0 0.5 0.0 —1-1-1-1-1-1-1-1-1-1-1-1-1-1-1-1-1-1-1-1-1-1-1-1-1-1-1-1-1-1-1-T- T i FE PB X MO X I PO X. MG i Hi T X T SE x x BL I CN i lO CNI CD CO O CO lO CD lO O tO CN CO tO o CN CN CO tO T— CN CN T- t— T— CN ENERGY / keV 0 0 0 Elsevier Editorial System(tm) for Applied Radiation and Isotopes Manuscript Draft Manuscript Number: ARI-D-11-00035 Title: A comparative study of radon-induced background in low-level gamma-ray spectrometers Article Type: Full Length Article Section/Category: Radioactivity and Radiation Measurements Keywords: Gamma-ray spectrometers, Radon-induced background, Attenuation coefficients, 226Ra Corresponding Author: Dr. Matjaz Korun, Corresponding Author's Institution: First Author: Petra Maver Modec Order of Authors: Petra Maver Modec; Matjaz Korun; Matej Martelanc; Branko Vodenk Manuscript Region of Origin: SLOVENIA Abstract: The radon-induced background of ten high-resolution germanium gamma-ray spectrometers was analyzed. In the analysis the apparent activity was introduced, which is defined as the peak count rate normalized with respect to emission probability and detection probability. On the basis of its energy and time dependence the contributions to the background count rates due to the radiation, penetrating the shield, and the radiation due to the contamination of the air with radon daughters, were determined. Manuscript 1 2 3 spectrometers 4 5 6 7 A comparative study of the radon-induced background in low-level gamma-ray 12 *1 3 1 P. Maver Modec1,z, M. Korun \ M. Martelanc3, B. Vodenik1 9 10 1' 11 12 13 14 Slovenia 15 3 16 Faculty of Computer and Information Science, Tržaška cesta 25, Ljubljana, Jožef Stefan Institute", Jamova cesta 39, Ljubljana, Slovenia 2 Jožef Stefan International Postgraduate School, Jamova cesta 39, Ljubljana, Slovenia Abstract: The radon-induced background of ten, high-resolution, germanium, 17 18 19 20 21 22 23 gamma-ray spectrometers was analyzed. In the analysis the apparent activity 24 25 was introduced, which is defined as the peak count rate normalized with respect 26 27 to the emission probability and the detection probability. On the basis of its 28 29 30 31 32 33 34 35 3 6 Keywords: Gamma-ray spectrometers, Radon-induced background, Attenuation 37 38 39 40 41 42 43 Introduction 44 45 46 47 48 49 50 51 52 235 53 gamma-rays interfere with the gamma-rays from the decay of U, which 54 55 56 57 energy and time dependence, the contributions to the background count rates due to the radiation penetrating the shield and the radiation due to the contamination of the air with radon daughters were determined. coefficients, 226Ra Gamma-ray spectrometry is a method that is not very sensitive when applied to activity measurements of 226Ra. This isotope radiates gamma-rays mainly at 186 keV, with a probability of about 3.5% (IAEA 2007). Unfortunately, these introduces an additional source of uncertainty to the measurement results of 58 * Corresponding author. Tel.:+386 1 4773 900; fax: +386 1 4773 151; E-mail address: 59 matjaz.korun@ijs.si (M. Korun). 60 61 62 63 1 64 1 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 samples containing uranium (Ebaid, 2009). For this reason, it might, therefore, be advantageous to determine the radium activity from the activity of the radon 214 214 daughters Pb and Bi, which radiate at many gamma-ray energies in the energy range from 200 keV to 2500 keV and at bismuth X-ray energies. The emission probabilities for these photons can reach up to 45%. Consequently, this indirect measurement method is more sensitive than a direct determination based on the 186-keV gamma-ray peak. If the activity of the 226Ra in the sample is small, a substantial part of the count rate of the peaks, signaling the presence of radon daughters, may originate from the spectrometer background. In the spectral analysis this systematic influence is accounted for by the subtraction of the background, i.e., the peak count rates measured in the absence of the sample. Therefore, it is of vital importance to accurately determine the radon-induced spectrometer background. The influence of radon daughters on the spectrometer background originates from the presence of the 226Ra in the detector, the shielding materials, the materials surrounding the spectrometer shield, where the rays penetrating the shield originate, and from the presence of radon daughters in the air that fills the shield's cavity. While the contributions from the contamination of the detector, the shielding materials and the environment are constant with time, the contribution due to the contamination of the air may vary. The concentration of radon daughters in the air in the cavity follows their concentration in the air in the counting room, which is not constant (WHO 2009). Therefore, the count rate 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 in the peaks in the background due to radon daughters may vary with time and cannot be determined as a simple average over the count rates obtained from repeated background measurements. The radon-induced background also increases the continuous spectral background, thereby affecting the measurement sensitivity for other gamma-ray emitters. It is the purpose of this contribution to present an analysis of the radon-induced background of the spectrometers installed in the Laboratory for Radiological Measuring Systems and Radioactivity Measurements in order to determine the sources of contamination, their location, their contribution to the background and its time dependence. Materials and Methods The counting room is located in a basement, below ground level. It is kept at a constant temperature and is not ventilated so as to avoid any possible contamination (the air is exchanged only as a result of the draught). This draught is stronger when there are low outdoor temperatures, since then the cooler air from the ambient of the building tends to replace the warmer air in the counting room. There is a large amount of radon entering the counting room because of the poor hydroisolation of the building. Radon can enter the room by advection through the gap between the foundation wall and the concrete floor slab, and by diffusion through the walls (UNSCEAR 2000). This advection is constant throughout the year since the temperature of the air in the counting room and the temperature of the soil are constant. However, the diffusion through the walls is 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 greater in summer, since during this time the atmospheric air cannot replace the subterranean air and dilute the radon that is there (Sundal et al, 2008). During the summer the radon concentration in the counting room may reach 600 Bq/m , 3 but in the winter the average concentration is 70 Bq/m . Diurnal variations of the radon concentration are not taken into account since the typical counting time for routine measurements lasts at least one day. The counting room houses ten spectrometers with high-resolution, germanium spectrometers that have a variety of different characteristics. The characteristics of the spectrometer shields are given in Table 1. However, the graded layers used to prevent the registration of the X-rays are omitted from the table in order to improve its clarity. The shield cavities, except for the cavities of the spectrometers PO and LE, are flushed constantly with nitrogen in order to remove the ambient air, which is contaminated with radon, from the interior of the shield. The nitrogen is obtained by evaporating liquid nitrogen, which is then aged for two weeks to allow the radon to decay. The average daily evaporation rate of the liquid nitrogen is ten liters. Because of the limited supply of nitrogen, some shields are not flushed completely; therefore, some contamination of the radon daughters may remain within the cavity. This is reflected in the seasonal variations of the background of the radon daughters in some spectrometers, which occurs in spite of the flushing. The seasonal variations of the count rate for the peak at 352 keV in the background measurements of the spectrometer MG, which has the largest shield cavity, are presented in Fig. 1. In Fig. 2 this peak count rate is presented as a function of the outdoor temperature, averaged 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 over the counting time of the measurement. The total count rate in the spectral energy interval from 45 keV to 2700 keV is larger by about 20% in the summer than in the winter for this detector. The background measurements are performed at times when samples for the activity measurements are not available. The acquisition time for the background measurements is between 3 days and 12 days. Like with other peaks occurring in the background spectrum, the count rate in the peaks of the radon daughters is determined from the measured spectra under the same peak-analyzing conditions as the sample spectra. Some of the peaks are not identified in all the background measurements because of the poor statistics or the poor deconvolution of the multiplets when the statistical uncertainties of the peak areas are high. Here we analyze only the count rates at energies where the peaks are recognized in a great majority of the measurements. These peaks occur at energies of 75 keV, 77 keV, 87 keV, 90 keV, 242 keV, 295 keV, 352 keV, 609 keV, 768 keV, 1120 keV, 1238 keV, 1765 keV, 2204 keV and 2448 keV. Some of these energies are omitted from the data on the spectrometers where the peaks are not recognized in the background measurements frequently enough. Also, the X-ray energies are omitted for the spectrometers where radon-daughter-induced peaks interfere with the peaks due to the fluorescence of the lead that constitutes the spectrometer shields and the uranium from the detector materials. Results 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 It is clear from Fig. 1 that the count rates in the background peaks may be subject to seasonal variations. However, below a critical outdoor temperature the count rate no longer depends on it, since at this point the radon concentration is low enough for the flushing to effectively remove all of the radon from the shield cavity. The effectiveness of the flushing depends on the volume of air in the cavity, the intensity of the flushing and the permeability of the shield with respect to the air. For the detectors that exhibit a temperature dependence, this critical temperature varies between 14 °C and 20 °C. The count rate below the critical temperature is determined, in addition to the detector efficiency, by the contamination of the detector and the shield with 226Ra and by the penetration rate of the gamma-rays from the counting room through the shield. Above the critical temperature the count rate increases linearly with the outdoor temperature. The rate at which it increases depends on the effectiveness of the flushing, the volume of the shield cavity and the efficiency of the detector. During the background measurements the detector measures the flux of gamma-rays at the center of the shield's cavity, where it is placed. To convert the count rates into gamma-ray fluxes, characterizing the contaminations, the response of the detector and the probability of the emission of the gamma-rays has to be taken into account. To assess the fluxes, the apparent activities A(E) are calculated as n( E) A( E) = ?]( E )b( E) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 where n(E) denotes the count rate in the peak at the energy E; q(E) is the counting efficiency of a point source, positioned at the detector surface on the symmetry axis of the detector cap, radiating gamma-rays with the energy E; and b(E) is the probability for the emission of gamma-rays with the energy E in a decay of a radon daughter. It is advantageous to use apparent activities for analyzing the background since they are smooth functions of the gamma-ray energy. It follows that the value of an apparent activity does not represent the result of an assessment of a true activity, but serves only for treating the count rates in peaks at different energies on an equal footing. It is possible to interpolate the apparent activities to energies, where the background peaks' count rates are too weak to be measured reliably. Also, from their energy dependence it is possible to deduce simplified models of shields for describing the transport of gamma-rays and compare the apparent activities in different spectrometers. It should be noted that the point-source efficiency, which is used for the calculation of the apparent activities, only poorly represents the average probability for the registration of a gamma-ray impinging at a large angle on the detector cap. The point-source efficiency used corresponds to a geometry where the rays impinge on the crystal under all angles, describing the probability for the registration of a photon emitted isotropically from a point source. Although the point-source efficiency used is a maximum, it still underestimates the average probability, except in the case of the contamination of the detector cap. Therefore, the apparent activities overestimate the flux rates, normalized to an 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 emission probability of unity. Fig. 3 presents the apparent activities, corresponding to count rates in the spectrum below the critical outdoor temperature, for the spectrometers installed in the counting room. Above the critical temperature, the background count rate is the sum of the count rate below the critical outdoor temperature and the contribution due to the variable concentration in the ambient air, which affects the contamination of the air within the shield cavity of the draught through the spectrometer shield. The count rate is described as: n'(E, T) = n(E) + k(E)( T - Tc ) , where T denotes the average outdoor temperature during the background measurement, Tc is the critical outdoor temperature and k(E) is the rate of increase of the background count rate in the peak at an energy E with temperature. Like with the apparent activity, the apparent activity due to the air contamination, normalized to the unit of the temperature increase above the critical temperature, can be calculated as = »'(EX) -n(E) = k(E) . " ' * E )b( E)( T - Tc) * E )6( E) For the detectors exhibiting a temperature dependence the increase in the apparent activity with temperature is presented in Fig. 4 at energies where the peaks in the background spectra are strong enough to allow its evaluation. For other detectors it can be assumed that the critical temperature exceeds the maximal average outdoor temperature where the background measurements were performed. The importance of the temperature dependence relative to the 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 temperature-independent background is presented in Table 2, together with the critical temperature Tc. The relative influence is calculated as the ratio of the rate of increase of the apparent activity with temperature AT(E) versus the temperature-independent apparent activity, averaged over the energies in the energy interval from 200 keV to 400 keV, where the apparent activity is at a minimum, and multiplied by the temperature difference between 25oC, which is the maximal average outdoor temperature, and the critical outdoor temperature Tc. This ratio gives the maximal relative influence of radon daughters in the air of the counting room on the radon-induced spectrometer background. Discussion It is clear from Fig. 3 that in the energy range above 500 keV the temperature-independent apparent activity increases with the energy in all the spectrometers, except LE and HG. The spectrometer LE has a low-energy detector, having a crystal with a thickness of only 1 cm having small peak efficiency at energies exceeding 500 keV. On the other hand, the detector HG has a very low background and the incidence of the detection of the radon-induced background peaks above an energy of 500 keV does not exceed 30%. In these circumstances the reliability of the peak analysis is not sufficient to yield trustworthy results. In other detectors, the apparent activity is an increasing function of the energy. This is due to the attenuation coefficient for the photons in the shielding material, which decreases with energy. The rate of increase carries information about the thickness of the material between the source of the photons and the detector. In the absence of ducts in the shielding, below 500 keV the photons 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 cannot penetrate the layers of the shielding; therefore, here the apparent activity, Ad, is given by the contamination of the detector and the inner surface of the cavity with the 226Ra. The increase of the apparent activities over this level indicates there are contributions from the shielding material and from the exterior of the shield. The count rate in the X-ray peaks is difficult to interpret in terms of contamination because of the X-ray fluorescence of lead, which interferes with 214 the X-ray peaks from the Bi that belong to the decay of the radon daughters. Namely, the graded layers (made of cadmium and copper) do not attenuate the fluorescence completely. They also interfere with gamma-rays from the decay of 235 the U at energies of 75 keV and 90 keV. In addition, the deconvolution of the multiplets is not reliable for the large statistical uncertainties of the peak areas. Therefore, the apparent activities at the energies that coincide with the energy of the lead X-rays (75 keV and 87 keV) are only given in cases where no lead is used in the shielding or where the inner layer absorbs the fluorescent X-rays completely and where the decomposition of the multiplets is reliable enough. They are also not given when gamma-rays from the uranium decay are present in the background spectrum. It is clear from Fig. 3 that the apparent activities calculated from the X-ray peak roughly reproduce the apparent activities due to the detector contamination, except on the spectrometer FE, where the increased apparent activity indicates the presence of lead within the detector. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 A rough estimate of the quality of the spectrometer shields, where an increase of the apparent activity at energies above 500 keV is observed, can be obtained from the ratio of the apparent activities at 1765 keV and 352 keV. The values of this ratio are presented in Table 3. The maximal value is attained for the spectrometer RA, which has an improvised lead shield and consequently a large penetration for high-energy gamma-rays. The next-highest values are associated with the spectrometers PO and BL, with portable detectors. Only the detector cap of these detectors is shielded, and therefore the gamma-rays impinging through the detector dewar are considerably less attenuated. The spectrometer SE has a portable detector as well, but its dewar is contained within the shielding together with the detector cap. The other spectrometers FE, PB, MO and MG have detectors with a vertical dipstick. The dipstick of the detector MG has an internal shielding that prevents the photons flying near the cold finger to impinge on the detector crystal. The spectrometer FE has an iron shield, which is reflected in a relatively high value of the ratio. If the spectrometer shield consists of only one layer, its effective thickness can be assessed from the increase in the apparent activity over its minimal value, AD. The flux inside the cavity can be expressed as A(E) - Ad = Aoe-Ms(E)psd , where ^S(E), pS and d denote the attenuation coefficient for the gamma-rays in the shield, the shield density and its thickness, respectively. A0 denotes the apparent activity in the absence of the shielding. At high energies this apparent activity depends only weakly on the energy, since here the attenuation 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 coefficient in the building materials, from which the gamma-rays are emitted, weakly depends on the energy. For the purpose of assessing the effective thickness of the shielding with an atomic number much higher than the average atomic number of the building materials it can be assumed to be independent of the energy. Then the assessment can be made on the basis of the increase of the apparent activity over AD at the lowest energy, where this increase is substantially larger than its uncertainty. For the detectors PB and RA, at 609 keV such an increase already occurs. Here, the effective thickness can be estimated from ln A(E) - Ad d{ E) =_A (6°9 keV) - AD . [Ms (6°9 keV) - m (E )]ps The effective thickness, calculated as a function of the energy, is presented in Table 4. In the detector RA a slight increase in the average thickness with energy indicates an additional attenuation outside the shield, i.e., in the material, where the gamma-rays are emitted. The relatively low average thickness for the detector PB points to a narrow duct where the detector is shielded with only approximately 1 cm of lead. For the detectors FE, MO and PO the effective thickness is assessed relative to the apparent activity at 1120 keV to 16 cm ± 2 cm, 9 cm ± 2 cm and 6 cm ± 1 cm, respectively. The values for the effective thickness reproduce well the average thickness of the shield, taking into account the variability of the shield thickness with respect to the direction of the impinging gamma-rays. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 For the spectrometers with a shield consisting of two layers, the flux of gamma-rays at the outer surface of the inner layer, AO(E), can be calculated from the increase of the apparent activity over its value AD, corrected for the attenuation of the gamma-rays in the inner layer. This is calculated as A0 (E) = (A(E) - Ad )eMl (E)dlP where ^i(E), di and p\ denote the attenuation coefficient, the thickness and the density of the material of the inner layer, respectively. This calculation can be performed for the spectrometers MG, SE and BL, having two-layered shields and exhibiting an increase in the apparent activity with energy. For the detector MG, which does not exhibit a constant apparent activity in the region 200-400 keV, a value of zero has been assumed for AD. The apparent activities AO(E) are presented in Fig. 5. it is clear from the figure that the apparent activity is independent of the energy for the detector MG. it follows that the contamination is located at the outer surface of the paraffin. Here, no evidence of the penetration of gamma-rays through the outer layer exists. On the other hand, the increase of the apparent activity for the detectors SE and BL indicates the penetration of the gamma-rays through the outer layer. The penetration is stronger in the spectrometer BL, since here the ratio AO(1120 keV)/AO(609 keV) is larger, which indicates a smaller effective thickness. The difference reflects the effectiveness of the shielding of the portable dewar of the spectrometer SE. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 The time dependence of the radon-induced background originates from the variable concentration of the radon in the air in the counting room, which affects the contamination of the air within the spectrometer cavity as a result of the draught through the shielding. The variations due to the draught were observed on the spectrometers LE, PO, MG, BL and RA. For these detectors the critical outdoor temperatures, where the background starts to increase, are 17 oC, 15 °C, 14 °C, 20 °C and 18 °C, respectively. The largest effect of the temperature dependence relative to the background below the critical temperature is observed at an energy of 295 keV. It is clear from Fig. 4 that the rate of the increase is, in the framework of the accuracy achieved, independent of the energy for the spectrometers LE, PO and BL. For spectrometers showing an energy-independent rate of increase AT it can be concluded that the contamination causing the temperature dependence is located within the shield cavity. Fig. 6 presents the rate of increase of the apparent activity A'T(E) for the spectrometer MG, corrected for the attenuation in the paraffin layer, calculated as A't (E) = At(E)eMp(E)ppdp , where ^P(E), pP and dP denote the attenuation coefficient of the gamma-rays, the density and the thickness of the paraffin layer. Since the corrected rate does not depend on the energy it follows that the corresponding contamination is located on the outer side of the paraffin layer. This deduction supports the conclusion regarding the location of the apparent activity on the detector MG. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 The rate of increase of the apparent activity with temperature, which is independent of the energy for all the spectrometers, except for the spectrometer RA, offers the opportunity to treat the temperature dependence of the radon-induced background at all energies on an equal footing. The spectrometer RA exhibits an energy dependence, since here the temperature dependence originates, at least partially, in the increased radon concentration in the air of the counting room, i.e., outside the lead shielding. It is obvious that here the high-energy gamma-rays penetrate through the shield with a probability that is high enough to detect variations in the concentrations of the radon daughters in the ambient air, although the variability of the background with the temperature is small compared to the background independent of the temperature. To describe the temperature dependence better, for the spectrometers LE, PO, MG and BL the average rates of increase were calculated. These averages are presented in Table 5. The largest average is exhibited by the spectrometer MG. Here the radon diffuses into the paraffin, causing its contamination with radon daughters. Although flushing the cavity prevents radon from entering the cavity, it does not prevent it from contaminating the paraffin. The cavities of the spectrometers LE and PO are not flushed, which results in a considerable temperature dependence, in spite of their low volumes. The high temperature dependence of the spectrometer BL is due to the relatively poor tightness of its shield and consequently to a large draught through its cavity. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 It should be noted that the increase in the background relative to that below the critical temperature can in some spectrometers easily exceed 100%. Therefore, it is of vital importance to take this into account, especially when measuring the 238 226 concentrations of the U and Ra in low-activity samples, such as the dry residue obtained after the evaporation of water, aerosol filters and water filters of suspended particulates, as described by Korun and Kovačič (2010). In routine measurements the time dependence of the background is taken into account via measurements of the outdoor temperature. The daily averages of the outdoor temperature are recorded and the background count rates during the measurement time are calculated. These count rates are used when correcting the peak count rates in the sample spectra. Conclusion For the ten spectrometers mounted in the counting room of the Laboratory for Radiological Measuring Systems and Radioactivity Measurements the sources of radon-induced background were determined. The apparent activity, which was introduced to connect the background count rates at different energies, proved to be a useful quantity enabling their systematic analysis. The contributions due to the penetration through the shield and the contamination of the air with radon daughters were determined on the basis of the energy and temperature dependence of the apparent activities. It was shown that in the case when the contamination resides within the shield, the temperature dependence of the apparent activity does not depend on the gamma-ray energy. Therefore, the 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 calculations of the time-dependent background count rates could be improved. Also, the background count rates in the peaks that are too weak to be analyzed reliably were determined. As a consequence, regarding the measurement results of low-activity samples, some systematic influences were removed and the uncertainties reduced. References: Ebaid, Y. Y., 2008. Use of gamma-ray spectrometry for uranium isotopic analysis in environmental samples, Rom. Journ. Phys. 55, 69 - 74 IAEA 2007: Update of X-ray and gamma-ray decay data standards for detector calibration and other applications, International Atomic Energy Agency, Vienna 238 Korun, M., Kovačič, K., Determination of U in ground water samples gamma-ray spectrometry. Appl. Rad. Isot. (2010), doi:10.1016/j.apradiso.2010.12.010. Sundal, A.V., Valen, V., Sodal, O., Strand, T., 2008. The influence of meteorological parameters on soil radon levels in permeable glacial sediments, Sci. Tot. Environ. 389, 418-428. UNSCEAR, 2000. Sources and effects of ionizing radiation. Report to the General Assembly with Scientific Annexes, YN, New York. WHO 2009: WHO handbook on indoor radon, WHO press, Geneva, Switzerland. Table 1. Characteristics of the detector shields Spectrometer code Inner layer Outer layer Volume of the shield cavity L Material Average thickness cm Material Thickness FE Iron 15 32 PB Lead 16 5 MO Lead 12 5 LE Plexy 2 Lead 10 1 PO Lead 10 2 MG Paraffin 10 Lead 12 34 SE Mercury 1 Lead 10 17 HG Mercury 1 Lead 12 11 BL Mercury 1 Lead 10 14 RA Lead 3-5 16 Table 2. The critical outdoor temperature Tc and the influence of the temperature dependence relative to the temperature-independent background for the detectors exhibiting a time variation of the radon-induced background. Detector code Critical outdoor temperature [oC] Relative influence LE 17 2.2 ± 0.3 PO 15 2.2 ± 0.3 MG 14 3.4 ± 0.3 BL 20 1.2 ± 0.1 RA 18 1.1 ± 0.2 Table 3. The ratio A(1765 keV)/A(352 keV) for the detectors exhibiting an increase of the apparent activity with energy. Detector code A(1765 keV)/A(352 keV) FE 4.9 ± 0.2 PB 3.9 ± 0.2 MO 2.3 ± 0.4 PO 7.6 ± 0.3 MG 1.9 ± 0.1 SE 2.5 ± 0.1 BL 6.3 ± 0.8 RA 33.1 ± 3.0 Table 4. The effective thickness of the shield for the spectrometers PB and RA calculated at energies exceeding 609 keV Energy [keV] Effective thickness [cm] PB RA 768 4.1 ± 0.6 1120 0.9 ± 0.1 4.0 ± 0.3 1238 2.1± 0.3 4.0 ± 0.4 1764 1.9 ± 0.1 4.4 ± 0.2 2204 2.6 ± 0.1 4.7 ±0.2 2447 4.8 ± 0.2 Table 5. The average rate of increase with temperature above the critical temperature of the apparent activity for different spectrometers Detector code LE PO MG BL Average rate [10-3 s-1 oC-1] 2.8 ± 0.8 10.9 ± 1.7 103 ± 6 15.4 ± 1.8 Figure captions: Fig. 1. Seasonal variations of the count rate of the peak at 352 keV in background measurements on the spectrometer MG Fig. 2. The temperature dependence of the count rate in the peak at 352 keV in the background measurements on the spectrometer MG Fig. 3. The energy dependence of the apparent activity A(E) for the ten spectrometers Fig. 4. The rate of increase of the apparent activity AT(E) at temperatures above the critical temperature Fig. 5. The energy dependence of the apparent activities AO(E) Fig. 6. The energy dependence of the rate of increase of the apparent activity for the detector MG, corrected for the attenuation in the paraffin layer, A' T(E) K) O K) J^ O hO O O Ul O O 75 77 87 90 242 295 352 609 768 1120 1238 1765 2204 2448 J ~i-r 73 > -D □ ] -] ] -] 00 -- t-r H □ H □ —I □ I - CD H 1 H □ ^ □ J_I__I_I__I_I__I_I__I_I__I_L ~i-r ~i-r D D CO m CD ~i-r TI O □ m -D □ -D -] ] TU-DO -D O o '(fl UJ 0.015 0.010 0.005 0.000 0.03 0.02 0.01 0.00 0.06 0.04 0.02 0.00 0.03 0.02 0.01 0.00 0.04 0.03 0.02 0.01 0.00 T x LE t T PO I I MG x x X X X I BL T T RA A r"i rn I oo o co m ^ co cdcncocdo-^ v v N N ENERGY / keV 0.6 CA ijj 0.4 0.2 0.0 0.3 0.2 0.1 0.0 0.4 0.2 0.0 T JL I MG SE BL x io r-- r--r-- Is- o co cn CN m cn cn m cn o CN CN 00 CO co o co m (D M O (D T- CN I-- O CN co CN CN ENERGY / keV o o UJ 0.15 - 0.10 - 0.05 - 0.00 m o oo cn (N m CN o oo CN cn m (N co co CD (N CO CN oo m CD ^ 00 o ^ CN ^ CN CN ENERGY / keV TRITIUM AND GAMMA-RAY EMITTERS IN SLOVENIAN GROUNDWATERS Katarina Kovacic • Jasmina Kožar Logar • Matjaž Aleš Korun Department of Low and Medium Energy Physics, Institute Jožef Stefan, Jamova cesta 39, SI-1000 Ljubljana, Slovenia. ABSTRACT. Concentrations of tritium, gamma-ray emitters in the uranium and thorium decay chains (U-238, Th-234, Pb-210, Ra-228, Ra-226 and Th-228) and potassium were measured in samples of ground water in Slovenia. Correlations among Ra-226, Ra-228 and Th-228 were observed in samples from intergranular and fractured aquifers. It was also found that the variability of tritium activity in intergranular aquifers is the largerest and in fractured ones the smallest. INTRODUCTION Slovenia gets a large proportion of drinking water from shallow alluvial, fractured and karstic aquifers which supply more than 97% of Slovenian population. In order to manage these groundwaters properly it is advantageous to know their properties and also their vulnerability. The Directive 2000/60/EC of the European Parliament and of the Council of 23 October 2000 sets out general provisions for the protection and conservation of groundwater for all Member States. To provide better regulation and control on groundwater environmental state the Ministry of the Environment and Spatial Planning of Slovenia established Rules determining the groundwater water bodies. According to the rules 21 water bodies were determined on the basis of existing hydrological, geological, pedological data, data on land use and anthropogenic load (OJ RS 2005). In 2008 a research project started with cooperation of the Jožef Stefan Institute, the Geological Survey of Slovenia and Ljubljana waterworks. The aim of the project is to find a suitable methodology that could provide us with the information about the age of the groundwater and the correlations between the dynamics, lithology and hydrogeological properties of the aquifers. With these data we will be able to assess the quality and vulnerability of aquifers in our country. The first step in reaching this goal was to achieve adequate data for tritium, gamma emitters, basic chemistry, microelements and concentration 15 13 18 of stable isotopes described by 5 N, 5 C, 5 O of all major aquifers across Slovenia as this was not done systematically until now. The sampling is still going on and is expected to end in the spring of 2011. In this contribution we will present the results of tritium and gamma-ray emitters from the year 2009 and the correlations between them. SAMPLING Sampling locations were determined according to geological properties of Slovenia region (primary network of monitoring sites) and some sampling sites were added locally (local network of monitoring sites) in connection with other projects. The primary network covers all existing lithologies in Slovenia region to assure data quality. First sampling started in autumn of 2008. In 2009 new locations were set and their sampling was done in spring and in autumn. The sampling of 2010 is not finished yet as the autumn sampling has not yet begun. All samples are collected at least 3 days after rainfalls to prevent their possible impact on groundwater properties. Samples are collected for tritium and gamma emitter measurements separately into 1-L polyethylene and 50-L containers, respectively. Samples for gamma emitters are acidified with nitric acid on the sampling site to a pH less than 2 in order to retain the radionuclides in the solution (ISO 2007). At the same time also the samples for determination of other parameters are taken. METHODS For tritium measurements, sample preparation was performed by electrolytic enrichment method, which consists of primary distillation, electrolytic enrichment and secondary distillation. Before any processing of samples in the laboratory, pH and conductivity were measured. In primary distillation 500 mL of sample is distilled in order to remove any impurities and other radionuclides that could interfere with tritium measurements. After the first distillation 1.5 g of sodium peroxide (Na2O2) is dissolved in 500 mL of sample aliquot to increase the conductivity to a value needed for the electrolytic enrichment process. During the electrolysis the samples are subject to a total charge of 1400 Ah and at the end their volume is reduced to approximately 15-20 mL. Samples are neutralized by adding 6 g of lead chloride (PbCl2) and distilled for the second time. Each electrolytic run includes beside 15 samples also 3 spike waters for the enrichment factor determination and 2 dead water samples for background measurement. At the end an aliquot (8 mL) of the final distillate is mixed with 12 mL of scintillation cocktail (Ultima Gold or Hi Safe 3) in a 20-mL polyethylene vial and measured in the Quantulus 1220 spectrometer. Samples are measured for 300 min, spiked samples for 100 min and background waters for 1000 min. In addition to electrolysed samples also non-enriched samples are measured to assure better control of the sample preparation process and to check the measurement. The sequence of all measurements was performed three times. The minimum detectable activitiy for tritium is 52 Bq/m . For measurements of gamma-ray emitters app. 50 L of sample is evaporated at a temperature of approximately 65°C in order to obtain the dry residue which is then measured on a gamma-ray spectrometer. The spectrometer has a planar germanium detector with a crystal having a diameter of 8 cm and thickness of 3 cm. The detector has a resolution of 0.6 keV at low energies and 2 keV at 1.3 MeV and is equiped with a beryllium window. The spectrometer has a lead shielding with inner layers of 1 cm of mercury, 2 mm of cadmium and 1mm of copper. It has a cosmic veto shielding reducing the continuous background to 0.7 cps in the energy range from 5 keV to 2.8 MeV. By gamma-ray spectrometry activity concentrations of U-238, Th-234, Ra-226, Pb-210, Ra-228 and Th-228 are determined. The minimum 3 detectable activities (decision thresholds) for these isotopes are 0.05 Bq/m for Th-228, 0.25 Bq/m3 for Ra-226, 0.3 Bq/m3 for Pb-210, 0.4 Bq/m3 for Ra-228, 1.5 Bq/m3 for U-238, 4 Bq/m3 for Th-234. RESULTS AND DISCUSSION Collected samples Until now we collected 158 samples of groundwater and 2 samples of surface water (same sampling location) from 69 different locations during the years 2008 (13 samples), 2009 (104 samples) and 2010 (43 samples). Samples are obtained from springs, boreholes and wells (Table 1). Locations were sampled two times (spring and autumn), except for the 2008 where sampling begun in autumn. Starting from year 2010 new sampling sites were selected. Tritium In Figure 1 the results from 45 locations from 2009 are presented as they were all sampled twice, in spring (from April to July) and in autumn (from October to December). According to 3 3 the average tritium activity for spring (676 ± 80 Bq/m ) and autumn (667 ± 75 Bq/m ) there is no significant difference between the two sampling periods. The minimal measured activity 33 for spring period was 144 ± 29 Bq/m (VR6275B) and for autumn period was 117 ± 14 Bq/m (VR2253). Two locations from autumn sampling showed results below minimal detectable activity (VR6275B and VR5290A). The maximal activity was measured in one place (VP2241) for both spring and autumn period and was 1189 ± 121 Bq/m and 1400 ± 131 Bq/m respectively. 17 sampling sites showed statistically different tritium activities (Figure 1) between spring and autumn, among these 9 showed increased activity in spring and 8 in autumn (for 10 samples data for autumn is not available). Comparing averages values for tritium activities in different types of aquifers (fractured aquifers have an average of 680 ± 84 Bq/m ; 33 intergarnular aquifers 727 ± 84 Bq/m and karstic aquifers 640 ± 71 Bq/m ) we also observed no significant differences. If tritium activities are plotted on a chart (Figure 2) we can observe that in the fractured aquifers the tritium concentration has the smallest variability, while in the intergranular aquifers the variability is the largest. From Figure 3 it follows that seasonal differences (calculated with U-test, describing the statistical significance of the difference of the measurement results) in comparison with aquifer porosity are more likely to occur on karstic and less on fractured aquifer. Besides comparing tritium activity we also compared pH values between the two seasons and based on the statistical results from Table 2 we concluded that there are no major statistical differences. Average pH for spring and autumn are 7.6 and 7.3 respectively which is within the range of pH for groundwater which is usually between 6.0 and 8.5 (Hem 1970). In spring samples higher pH values were measured as in autumn samples. Gamma emitters Generally the activities of gamma emitters in the collected samples are near detection limits, so the counting statistics is the main source of uncertainty of the measurement result. To improve the counting statistics of radionuclides and to assess the activity concentration of Th-234 at the sampling time the samples were measured twice. The first measurement was performed as soon as possible after the evaporation and the second after a few half lives of Th-234. From the activity concentrations of U-235 and Th-234 at both measurement times the concentration of U-238 and Th-234 at sampling time was determined (Korun and Kovačič, submitted for publication). Because of the need of two measurements we present here only 30 results (Table 3). For these samples we present measurement results also for Ra-228, Th-228 and Ra-226 as the weighted mean of both measurements. The concentration of Th-234 was under the decision threshold in all samples. For Pb-210 and K-40 we present 94 results as their evaluation does not need two measurements. The averages of the raw observation (activities calculated from the peak areas) were converted into the expected activity values using Bayesian statistics (Korun and Maver Modec 2010) taking into account the fact that activity concentrations can not be negative. Usually the concentration of thorium in water is low, because of its low solubility, but it can increase due to formation of soluble complexes with carbonate, humic materials or other ligands in the water (Jia et al. 2008). Correlations between radionuclides were made according to different types of aquifer porosities (fractured, intergranular and karstic). Below we present two of the most interesting results. Please note that the error bars for karstic aquifers were omitted, because of the clarity. In Figure 4 it can be observed that the correlation between Th-228 versus Ra-228 is high in intergranular and fractured aquifers, no correlation between these two radionuclides seems to occur in the karstic aquifers. The same is observed in the Figure 5 where the correlation between Ra-226 versus Ra-228 is presented. Table 4 presents the correlation factors between radionuclides (U-238, Th-228, Ra-228 and Ra-226) for different types of aquifer porosities. For the intergranular porosity the correlations are very strong between Th-228, Ra-228 and Ra-226. A smaller correlation among these radionuclides is seen also in fractured type (this could be also because fewer samples are available for intergranular type and thus the correlation is better). The correlations among these radionuclides could be the consequence of lower permeability factor of intergranular and fractured aquifers in comparison with karstic ones, which allows the establishment of the balance between the host rock and the groundwater. The high correlation between Th-228 and Ra-228 in the case of fractured and intergranular aquifers reflects the fact that Ra-228 is the parent radionuclide of Th-228 with a half-life of app 5.8 years. In the case of karstic aquifers the absence of correlation between these two radionuclides can be explained by the higher permeability factor and therefore the equilibrium between water and rock cannot be established. Pb-210 and K-40 with tritium The correlations between K-40 and Pb-210 with tritium for different types of aquifer porosities are presented on Figures 6 and 7. It can be observed that no correlation exist between before mentioned radionuclides. Intergranular types of aquifers tend to have higher K-40, whereas karstic aquifers tend to have lower Pb-210 concentration. Figures 8, 9 and 10 present the correlation between Pb-210 and K-40 for different groundwater sources. It can be seen that lower activity values of K-40 are found in springs and a slight correlation between the two radionuclides is also observed. CONCLUSIONS It was observed that correlations between radionuclides depend on the type of the aquifer (intergranular, fractured or karstic) as the consequence of different permeability coefficients. When the permeability coefficient is low the available time for reaching the equilibria between radionuclides in the water and rocks is longer than in the case when the coefficient is high. The strongest correlation is observed among Th-228, Ra-228 and Ra-226 in intergranular and fractured aquifers. In the case of tritium bigger variability of its concentrations in intergranular aquifer is observed while in fractured the variability is the smallest. Intergranular types of aquifers tend to have higher K-40, whereas karstic aquifers tend to have lower Pb-210 concentration. To confirm these conclusions more samples will be analysed. REFERENCES OJ RS 2005. Pravilnik o določitvi vodnih teles podzemnih voda.- Official Journal of the Republic of Slovenia. 6532. Jia G, Torri G, Ocone R, Di Lullo A, De Angelis A, Boschetto R. 2008. Determination of thorium isotopes in mineral and environmental water and soil samples by a-spectrometry and the fate of thorium in water. Applied Radiation and Isotopes 66:1478-1487. Hem JD. 1970. Study and Interpretation of the Chemical Characteristics of Natural Water. Second edition. Untited states government printing office, Washington. ISO. 2007. Water quality - Determination of the activity concentration of radionuclides - Method by high resolution gamma-ray spectrometry. 10703:2007 (E) Korun M, Kovacic K. (submitted for publication in Applied Radiation and Isotopes) Korun M, Maver Modec P. 2010. Interpretation of the measurement results near the detection limit in gamma-ray spectrometry using Bayesian statistics. Accreditation Quality Assurance 15:515-520. Table 1 Year Season All samples Springs Boreholes Wells Surface water 2008 Autumn 13 1 6 6 / 2009 Spring 58 34 17 6 1 Autumn 46 33 5 7 1 2010 Spring 43 31 9 3 / Spring 2009 Autumn 2009 pH Cond. (pS/cm2) pH Cond. (pS/cm2) Average 7.6 428.9 7.3 413.5 Min 6.6 69.8 6.0 82.4 Max 9.2 1364.0 9.1 1318.0 U-238** (Bq/m3) Ra-226 (Bq/m3) Pb-210* (Bq/m3) Ra-228 (Bq/m3) Th-228 (Bq/m3) K-40* (Bq/m3) Average 6.00 ± 0.64 1.78 ± 0.20 5.2 ± 0.7 0.90 ± 0.2 0.20 ± 0.07 23.8 ± 2.9 Min 1.25 ± 0.50 0.20 ± 0.12 0.50+ 0.25 0.11 ± 0.07 0.05 ± 0.04 1.6 ± 0.7 Max 16.9 ± 1.7 16.2 ± 0.9 32.8 ± 2.0 5.1 ± 0.3 0.95 ± 0.08 308 ± 32 *For Pb-210 and K-40 results from 94 results **For U-238 only 20 results were available Ra228- Th228- Th228- U238- U238- U238- Ra226 Ra226 Ra228 Ra226 Th228 Ra228 Fractured (10) 0.88 0.88 0.93 -0.35 -0.10 -0.23 Intergranular (6) 0.94 0.83 0.97 0.18 0.28 0.40 Karstic (14) 0.53 0.00 -0.29 0.76 0.65 0.35 TABLE CAPTIONS Table 1 Number of all samples collected from 2008 until today according to their source. Table 2 Average, minimal and maximal values for pH and conductivity for spring and autumn 2009. Table 3 Average, minimal and maximal activity of gamma emitters based on 30 results. Table 4 Correlation factors between radionuclides for different types of aquifer porosities (in parenthesis the number of samples is given). Tritium activity (Bq/m3) oooooooooo VP5230B VP8281 VP5216 VP5270 VP6250 VP1242 VP5232 VP1301 VP5280 VP1331 VP8361 VP5271 VP5230A VR5291B VR6275B ( VR5290A B VR5290B (/) ^ VP5224 3" CFQ VP5230 M o VP1000 vo VP3205 ■ VP3342 Q) C VP8333 g VP4246 VP6232 O VP1423 U3 VP1360 VP6242 VP5272 VP6275 VP4264 VP8276 VP2392 VP4224 VP2241 VP2319 VP2382 VP4223 VR6223 VR8262 VR2253 VR5291A VR2327 VR5291C VR6222 CfQ C rD O C J3 m C/5 CO M i 1600 1400 1200 1000 800 600 400 200 0 --i*-»* ■ •—// \ 20 40 60 samples 80 100 A fractured • intergranular • karstic 1,20 1,00 0,80 0,60 m 8 0,40 -0,20 0, + + 00 1,00 2,00 3,00 4,00 Ra-228 (Bq/m3) 5,00 6,00 A fractured »intergranular »karstic 6,00 5,00 E 4,00 3,00 2,00 1,00 0,00 m vc in in (0 cc + 0,00 1,00 2,00 3,00 4,00 Ra-228 (Bq/m3) 5,00 6,00 A fractured • intergranular • karstic 65,00 55,00 ^ 45,00 M I 35,00 m o 25,00 * 15,00 5,00 -5,00 ♦ a.. ja ai > 'A A - V • * 200 400 600 800 1000 1200 1400 1600 H-3 (Bq/m3) A fractured • intergranular • karstic m o