Development of Analytical Methodologies for Rapid Determination of Alpha and Beta Emitters by Liquid Scintillation Spectrometry in Water Samples

[eng] In this thesis the development of different methodologies for the rapid determination of alpha and beta emitters by liquid scintillation spectrometry is described. The feasibility of PLS model construction for the decombolution of the spectra obtained with the proposed methodologies was studied. Finally, the developed methodologies together with multivariate calibration have been organized in a strategy for the quantification of the radionuclides included in the annex III of the directive 2013/51/EURATOM. The methodologies developed in this thesis are; the simultaneous determination of gross alpha and gross beta by liquid scintillation spectrometry, and the determination of 226Ra, 228Ra and 210Pb using Radium RAD disk and liquid scintillation spectrometry. The simultaneous determination of gross alpha and gross beta is based on a concentration of the sample by evaporation. The evaporated sample is measured by liquid scintillation spectrometry with the value of the instrumental parameter for α/β separation optimized using 236U as pure alpha emitter and 40K as pure beta emitter. Spectra obtained by means of this methodology are not just useful for quantify global alpha and beta activities but also for the quantification of specific radionuclides using the decombolution with PLS models. The determination of 226Ra, 228Ra and 210Pb is based on the filtration of 1 L of the sample through a filter which selectively retains lead and radium isotopes. Lead isotopes, mainly 210Pb, are removed from the filter with a solution of di-hydrogen ammonium citrate (DHC). 210Pb is determined by liquid scintillation spectrometry from the eluted fraction while radium isotopes (226Ra and 228Ra) are determined directly from the RAD disk introducing it into a counting vial and measuring by liquid scintillation spectrometry. To avoid interferences in the quantification of the RAD disk is necessary to achieve an appropriate impregnation of the filter. For this aim the elapsed time between the sample preparation and the measure have to be eight hours at least. Alternatively, scintillation cocktail can be forced to pass through the RAD disk to ensure a correct impregnation. The construction of PLS models for the analysis of liquid scintillation spectra requires from a data base of spectra which is constructed with the experimental work performed along this thesis. Finally, a strategy for the determination of the radionuclides included in the annex III of the directive 2013/51/EURATOM using the developed methodologies and PLS models, is described. This strategy has been used total or partially for the determination of natural and artificial radionuclides with suitable results.[cat] En la present tesi es descriu el desenvolupament de diferents mètodes ràpids per a la determinació d’emissors alfa y beta per escintil·lació líquida. S’estudia la viabilitat de la construcció de models PLS per a la deconvolució dels espectres obtinguts amb els mètodes desenvolupats per a quantificar radionúclids específics. Finalment, els mètodes desenvolupats juntament amb la quantificació mitjançant calibratge multivariant amb models PLS s’han organitzat sota una estratègia per a la quantificació dels radionúclids llistats en l’annex III de la directiva 2013/51/EURATOM. Els mètodes desenvolupats son; la determinació simultània dels índex d’activitat alfa i beta total mitjançant escintil·lació líquida, i la determinació simultània de 226Ra, 228Ra i 210Pb en aigües mitjançant Radium RAD disk i mesura per escintil·lació líquida. La determinació dels índex d’activitat alfa i beta total es realitza mitjançant la concentració per evaporació de la mostra i la mesura directa d’aquesta mostra concentrada per escintil·lació líquida, emprant com a valor del paràmetre instrumental per a la separació α/β (PSA) optimitzat amb 236U com a emissor alfa pur i 40K com a emissor beta pur. Els espectres obtinguts amb aquest procediments, a banda de proporcionar informació global sobre l’activitat alfa i beta de la mostra, son aptes per a la quantificació de radionúclids específics mitjançant models PLS. En la determinació de 226Ra, 228Ra i 210Pb emprant Radium RAD disk es filtra 1 L de mostra a traves del filtre que reté de forma selectiva isòtops de radi i plom. Els isòtops de plom, bàsicament 210Pb, s’extrauen del filtra amb una solució de di hidrogen citrat d’amoni (DHC). El 210Pb es determina per escintil·lació líquida a partir de la fracció eluïda, mentre que els isòtops de radi (226Ra i 228Ra) es determinen directament per espectrometria d’escintil·lació líquida introduint el RAD disk en un val i afegint còctels. Per poder realitzar la mesura en aquestes condicions es necessari assolir una correcta impregnació del RAD disk. Amb aquesta finalitat, cal esperar vuit hores des de la preparació el vial fins a la mesura. Alternativament, es pot filtrar còctel a traves del RAD disk després del filtrat de la mostra per assegurar un correcta impregnació del filtre. L’anàlisi d’espectres d’escintil·lació liquida mitjançant la construcció de models PLS requereix una se de dades d’espectres que s’ha elaborat en el treball experimental de la present tesi. En aquesta base de dades s’han considerat els radionúclids llistats a la directiva 2013/51/EURATOM, amb diferents nivells d’activitat i considerant l’esmorteïment químic i de color. Finalment, s’ha definit una estratègia d’aplicació de les metodologies optimitzades, juntament amb l’ús de models PLS, per a la quantificació dels radionúclids inclosos en l’annex III de la directiva 2013/51/EURATOM. Aquesta estratègia, de forma total o parcial, s’ha aplicat a diferents tipus de mostra per a la quantificació de radionúclids naturals i artificials, amb resultats satisfactoris

DECLAB: a software for liquid scintillation spectra deconvolution

The deconvolution of liquid scintillation (LS) spectra is meaningful in several scenarios like supporting incomplete radiochemical separations, for screening purposes and determining different isotopes of the same element, which is explored in this paper for the case of 89Sr/90Sr. In this paper DECLAB, an online application for liquid scintillation spectra analysis is presented. The software considers the classical calibration modes like constant efficiency and quenching curve and furthermore, the deconvolution of multicomponent spectra by means of Partial Least Square Regression. DECLAB is designed to analyse Perkin Elmer Wallac Quantulus 1220 spectra. However, in further upgrades, the applicability of this tool will be extended to other LS spectrometers

Simultaneous determination of gross alpha, gross beta and Ra-226 in natural water by liquid scintillation counting.

The determination of gross alpha, gross beta and 226Ra activity in natural waters is useful in a wide range of environmental studies. Furthermore, gross alpha and gross beta parameters are included in international legislation on the quality of drinking water [Council Directive 98/83/EC].1 In this work, a low-background liquid scintillation counter (Wallac, Quantulus 1220) was used to simultaneously determine gross alpha, gross beta and 226Ra activity in natural water samples. Sample preparation involved evaporation to remove 222Rn and its short-lived decay daughters. The evaporation process concentrated the sample ten-fold. Afterwards, a sample aliquot of 8 mL was mixed with 12 mL of Ultima Gold AB scintillation cocktail in low-diffusion vials. In this study, a theoretical mathematical model based on secular equilibrium conditions between 226Ra and its short-lived decay daughters is presented. The proposed model makes it possible to determine 226Ra activity from two measurements. These measurements also allow determining gross alpha and gross beta simultaneously. To validate the proposed model, spiked samples with different activity levels for each parameter were analysed. Additionally, to evaluate the model's applicability in natural water, eight natural water samples from different parts of Spain were analysed. The eight natural water samples were also characterised by alpha spectrometry for the naturally occurring isotopes of uranium (234U, 235U and 238U), radium (224Ra and 226Ra), 210Po and 232Th. The results for gross alpha and 226Ra activity were compared with alpha spectrometry characterization, and an acceptable concordance was obtained