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A Low-Background Liquid-Scintlllation Counter for the Assay of Low-Specific Activity Tritiated Water; Compteur a scintillations a liquides, a faible mouvement propre, pour le dosage d'eau tritiee en faible activite specifique; ZHidkostnyj stsintillyatsionnyi schetchik s nizkim fonom dlya analiza nasyshchennoj tritiem vody s nizkoj udel'noj aktivnost'yu; Contador de centelleador liquido de reducida actividad de fondo para el analisis de agua pritiada de baja actividad especifica

Conference:

Abstract

In liquid-scintillation counting of tritiated water single photomultiplier counters and coincidence systems offer comparable sensitivities. To investigate low level counting a coincidence system was selected to avoid Uncertainties in the background due to single photon events arising from phosphorescence and chemiluminescenc e in the solution. With this system the background was found to be due largely to light originating in the photomultiplier photocathode. Using two photomultipliers with ''Pyrex'' photocathodes in contact in an 8 in thick iron shield experiments were conducted to determine the relative importance of the following possible courses of background : (a) Ionization and excitation of residual gas and of the semi-conductor dynode surfaces, particularly in regions where the current density is greatest. (b) Sparking, electroluminescence and field emission. (c) Positive ion feedback to the photocathode causing secondary electron emission. (d) Operation of the photocathode window itself as a phosphor for cosmic radiation, K{sup 40} beta particles or radiation from uranium daughter products. In particular it was found that contribution (c) was significantly lower than was previously supposed. Methods of minimizing these effects, including the use of quartz photocathodes, and special photomultipliers were investigated. In the finished design of counter the minimum detectable specific activity with a  More>>
Authors:
Boyce, I S; Cameron, J F [1] 
  1. Wantage Research Laboratory, Wantage (United Kingdom)
Publication Date:
Jan 15, 1962
Product Type:
Conference
Resource Relation:
Conference: Symposium on Tritium in the Physical and Biological Sciences, Vienna (Austria), 3-10 May 1961; Other Information: 7 figs., 10 tabs., 19 refs.; Related Information: In: Tritium in the Physical and Biological Sciences. V. 1. Proceedings of a Symposium| 380 p.
Subject:
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY; COSMIC RADIATION; DAUGHTER PRODUCTS; ELECTROLUMINESCENCE; ELECTRON EMISSION; EXCITATION; FIELD EMISSION; LIQUIDS; PHOSPHORESCENCE; PHOTOCATHODES; PHOTOMULTIPLIERS; SCINTILLATION COUNTING; SENSITIVITY
OSTI ID:
22028521
Research Organizations:
International Atomic Energy Agency, Vienna (Austria)
Country of Origin:
IAEA
Language:
English
Other Identifying Numbers:
Other: ISSN 0074-1884; TRN: XA12R0273116787
Submitting Site:
INIS
Size:
page(s) 231-247
Announcement Date:
Jan 18, 2013

Conference:

Citation Formats

Boyce, I S, and Cameron, J F. A Low-Background Liquid-Scintlllation Counter for the Assay of Low-Specific Activity Tritiated Water; Compteur a scintillations a liquides, a faible mouvement propre, pour le dosage d'eau tritiee en faible activite specifique; ZHidkostnyj stsintillyatsionnyi schetchik s nizkim fonom dlya analiza nasyshchennoj tritiem vody s nizkoj udel'noj aktivnost'yu; Contador de centelleador liquido de reducida actividad de fondo para el analisis de agua pritiada de baja actividad especifica. IAEA: N. p., 1962. Web.
Boyce, I S, & Cameron, J F. A Low-Background Liquid-Scintlllation Counter for the Assay of Low-Specific Activity Tritiated Water; Compteur a scintillations a liquides, a faible mouvement propre, pour le dosage d'eau tritiee en faible activite specifique; ZHidkostnyj stsintillyatsionnyi schetchik s nizkim fonom dlya analiza nasyshchennoj tritiem vody s nizkoj udel'noj aktivnost'yu; Contador de centelleador liquido de reducida actividad de fondo para el analisis de agua pritiada de baja actividad especifica. IAEA.
Boyce, I S, and Cameron, J F. 1962. "A Low-Background Liquid-Scintlllation Counter for the Assay of Low-Specific Activity Tritiated Water; Compteur a scintillations a liquides, a faible mouvement propre, pour le dosage d'eau tritiee en faible activite specifique; ZHidkostnyj stsintillyatsionnyi schetchik s nizkim fonom dlya analiza nasyshchennoj tritiem vody s nizkoj udel'noj aktivnost'yu; Contador de centelleador liquido de reducida actividad de fondo para el analisis de agua pritiada de baja actividad especifica." IAEA.
@misc{etde_22028521,
title = {A Low-Background Liquid-Scintlllation Counter for the Assay of Low-Specific Activity Tritiated Water; Compteur a scintillations a liquides, a faible mouvement propre, pour le dosage d'eau tritiee en faible activite specifique; ZHidkostnyj stsintillyatsionnyi schetchik s nizkim fonom dlya analiza nasyshchennoj tritiem vody s nizkoj udel'noj aktivnost'yu; Contador de centelleador liquido de reducida actividad de fondo para el analisis de agua pritiada de baja actividad especifica}
author = {Boyce, I S, and Cameron, J F}
abstractNote = {In liquid-scintillation counting of tritiated water single photomultiplier counters and coincidence systems offer comparable sensitivities. To investigate low level counting a coincidence system was selected to avoid Uncertainties in the background due to single photon events arising from phosphorescence and chemiluminescenc e in the solution. With this system the background was found to be due largely to light originating in the photomultiplier photocathode. Using two photomultipliers with ''Pyrex'' photocathodes in contact in an 8 in thick iron shield experiments were conducted to determine the relative importance of the following possible courses of background : (a) Ionization and excitation of residual gas and of the semi-conductor dynode surfaces, particularly in regions where the current density is greatest. (b) Sparking, electroluminescence and field emission. (c) Positive ion feedback to the photocathode causing secondary electron emission. (d) Operation of the photocathode window itself as a phosphor for cosmic radiation, K{sup 40} beta particles or radiation from uranium daughter products. In particular it was found that contribution (c) was significantly lower than was previously supposed. Methods of minimizing these effects, including the use of quartz photocathodes, and special photomultipliers were investigated. In the finished design of counter the minimum detectable specific activity with a counting time of 30 min. is 6x10{sup 7} {mu}c/ml. (author) [French] Dans le dosage de l'eau tritiee au moyen d'un compteur a scintillations a liquides, les compteurs a photomultiplicateur unique et les ensembles a coincidences presentent une sensibilite du meme ordre. Pour faire des recherches sur la mesure des faibles activites, les auteurs ont choisi un dispositif monte en coincidence, afin d'eviter les incertitudes dans le mouvement propre causees par l'apparation de photons isoles, dus a la phosphorescence et a la chimioluminescenc e de la solution. Dans ce dispositif, on a constate que le mouvement propre provient surtout de la lumiere qui emane de la photocathode du photomultiplicateur. En utilisant deux photomultiplicateurs a photocathode en pyrex, en contact dans une protection en fer de 20 cm, on a procede a des experiences pour determiner l'importance relative des phenomenes ci-apres pouvant constituer le mouvement propre: a) Ionisation et excitation des gaz residuels et des surfaces des dynodes a semi-conducteurs, notamment aux endroits ou la densite du courant est la plus elevee; b) Production d'etincelles, electroluminescence et emission du champ; c) Retroaction positive des ions vers la photocathode, provoquant une emission d'electrons secondaire; d) Fenetre de la photocathode jouant elle-meme le role de scintillateur pour les rayons cosmiques, les particules beta du {sup 40}K et les rayonnements emis par les produits de filiation de l'uranium. Les auteurs ont notamment etabli que le facteur c) avait sensiblement moins d'importance qu'on ne l'avait suppose precedemment. Ils ont fait des recherches sur les methodes permettant de reduire ces effets au minimum, notamment en utilisant des photocathodes en quartz et des photomultiplicateurs speciaux. Avec l'ensemble de comptage concu par les auteurs, l'activite specifique minimum decelable est de 6x10{sup 7} {mu}c/ml, le temps de comptage etant de 30 minutes. (author) [Spanish] Cuando se trata de efectuar el recuento de agua tritiada dor centelleo de liquidos, los contadores de fotomultiplicador unico y los dispositivos de coincidencias presentan sensibilidades comparables. Con el fin de efectuar estudios sobre la medicion fe bajas actividades, los autores eligieron un sistema de coincidencias para evitar la incertidumbre en lo que respecta a la actividad de fondo debida a fotones aislados emitidos en virtud de la fosforescencia y quimioluminiscenci a de la solucion. Los autores comprobaron que, en este sistema, la actividad de fondo proviene principalmente de la luz que emana del fotocatodo del fotomultiplicador. Utilizando dos fotomultiplicadores con fotocatodos de pyrex en contacto, encerrados en un blindaje de hierro de 20 cm de espesor, hicieron experimentos para determinar la importancia relativa de las siguientes posibles causas de la actividad de fondo: a) Ionizacion y excitacion del gas residual y de las superficies del dinodo semiconductor, especialmente en las regiones en que la densidad de corriente es maxima; b) Formacion de chispas, electroluminiscencia y emision de campo; c) Realimentacion de iones positivos al fotocatodo, que provoca una emision de electrones, secundarios ; d) Funcionamiento de la propia ventana fotocatodica en caracter de ''fosforo'' para la radiacion cosmica, las particulas del {sup 40}K o las radiaciones de los productos de filiacion del uranio. Los autores comprobaron que, en particular, el factor c) interviene en una proporcion mucho menor que lo que se habia supuesto. Estudiaron metodos para reducir a un minimo estos efectos, incluyendo el uso de fotocatodos de cuarzo y fotomultiplicadores especiales. Con el dispositivo disenado por los autores, la minima actividad especifica detectable, con un tiempo de recuento de 30 min, asciende a 6 x 10{sup 7}{mu}c/ml. (author) [Russian] Pri schege zhidkostnykh stsintillyatsij nasytsennoj tritiem vody schetchiki s odnim fotoumnozhitelem i sistemy sovpadenij dayut pokazaniya sravnitel'noj chuvstvitel'nosti. Dlya issledovaniya scheta izlucheniya maloj intensivnosti byla primenena sistema sovpadenij dlya togo, chtoby izbezhat' neopredelennosti v fone, vyzyvaemom izmeneniemi odnogo fotona v rezul'tate fosforestsentsii i khimicheskoj lyuminestsentsii v rastvore. Bylo obnaruzheno, chto vozniknovenie fona v ehtoj sisteme ob{sup y}asnyaetsya glavnym obrazom dejstviem sveta, iskhodyashchego iz fotokatoda fotoumnozhitelya. Byli provedeny ksperimenty s primeneniem dvukh fotoumnozhitelej s fotokatodami Pireks v kontakte s zheleznym ehkranom tolshchinoj v 8 dyujmov dlv opredeleniya otnositel'noj vazhnosti sleduyushchikh vozmozhnykh faktorov fona: a) Ionizatsiya i vozbuzhdenie ostatochnogo gaza i poverkhnostej poluprovodnikovogo dinoda, osobenno v tekh zonakh, gde imeetsya samaya bol'shaya plotnost' potoka; b) Iskroobrazovanie , ehlektrolyuminestsentsiya i avtozlektronnaya ehmissiya; c) Obratnaya svyaz' polozhitel'nykh ionov s fotokatodom, chto vyzyvaet vtorichnuyu ehlektronnuyu emissiyu; d) Samostoyatel'noe dejstvie fotokatodnogo okna podobno lyuminoforu kosmicheskoj radiatsii, beta-chastitsam K{sup 40} ili radiatsii dochernikh produktov urana. V chastnosti, bylo obnaruzheno znachitel'no men'shee vozdejstvie faktora, chem ranee predpolagalos'. Byli issledovany metody umen'sheniya ehtikh vozdejstvij, vklyuchaya ispol'zovanie kvartsevykh fotokatodov i spetsial'nykh fotoumnozhitelej. V okonchatel'noj konstruktsii schetchika miiimal'nayaobiaruzhim aya udel'naya aktivnost' so vremenem scheta v 30 minut sostavlyaet 6 x 10{sup 7} mikrokyuri na milillitr. (author)}
place = {IAEA}
year = {1962}
month = {Jan}
}