Hubbs, J.C.

Nierenberg, W.A.

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Lawrence Berkeley National LaboratoryRecent WorkTitleSCINTILLATION DETECTION OF VERY-LOW-ENERGY GAMMA RAYSPermalinkhttps://escholarship.org/uc/item/1p19918hAuthorsHubbs, J.C.Nierenberg, W.A.Publication Date1956-06-04eScholarship.org Powered by the California Digital LibraryUniversity of California... ' .,, .~ UCRL -3434 dy.) UNIVERSITY OF CALIFORNIA Erni8t0£awrence adiation TWO-WEEK LOAN COPY This is a library Circulating Copy which may be borrowed for two weeks. For a personal retention copy, call Tech. Info. Diuision, Ext. 5545 BERKELEY, CALIFORNIA DISCLAIMER This document was prepared as an account of work sponsored by the United States Government. While this document is believed to contain correct information, neither the United States Government nor any agency thereof, nor the Regents of the University of California, nor any of their employees, makes any warranty, express or implied, or assumes any legal responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by its trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof, or the Regents of the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof or the Regents of the University of California. · I ·' ··. :··~ I '. I· i - ' . . .... . , I ' r ~ • ·l ' .. I • ~ ' 1 . ·' .. t f ' . UNIVERSITY OF. C.!LlFOR.NlA Radiation Laboratory Berkeley,·. C_al i~rnia · ~nba<;t. No. w -?405 .. «~.g-48 · -:-·__._.. .. __ .... UCRL .. 3434 Physics Distribution . SCINTlLLA:TtON DETltCTtON OF VERY•LOW•ENEllGY GAMMA RAYS ·1. C. Hu'bb'$ and w. A. Nierenberg . .fwe 4, 19 56 . •,·. . ..... Printed for tbe U. S. Atomle Energy Commission . •. I ·.-1 ·~ .. ~ . ~ . ..- -- .. ..,' ,. - -- . . . . SCINTlLLATlON DETECTION OF VERY·LOW•ENEl\GY QAMMA RAYS* . . . . . ~ > • • • • . _-, l. C,. Hubbe and W. A~ Nierenberg Radiation J.,abo:ratory and ~partrnent of Pbyflllc!G Unl~eralty of Cal:i£oruta, Bet-keley, California . • .. . .~ . lune -4, '1956 ABSTRACT . · . .. · .... A method te t«tpoi'ted foJ' ... ·detecti~ o£ very..tow•energy gamma_. : · ~-·'.. · ,··;-='.r~ya. · 'l'he method utUtzea ~el#tlllation det4fction wit11 Nal·Tll c:ryetale eepe·· • I . . . . .. --- ·-- . .. . · · .. )r •• • • .9tally spllt and tn01.fA:ted for the. work, uu:l s•lected tlngl~ 5819 or 629Z piloto-.. · ,~;:~;~:· ·. >. in~tipUel"$• Typical performaace l~t u.nlt {Zv) efficiency with background of 1 · · ~< ·.".· ;i..;-·count·per· fuin\\t~ io~ gam.-n:a. energies between 5 and 100 ke-v. ,, .·· . . .' .. ~· ' lNTl\ODUCTION . . . I . : . ·. . , . . . · A study o£ the propertie$. ol the neutron.ode(tclet).t rubidiu~ isotopes ·.' :·~·;.:,\' _·: ·. 'b~Jh~ method of a~ornic beam8.:1 has prompted ·the development· of higb .. e!fid~ney .... ::: .··, ·;·:.lo~·bac~gro®cl counters to clet~c;~ k x-ray$ (""15 kev) ~~mltted when .e mate• I' '., • ~ :·· • ' '- • •' . . ' 1, ~· ,·<': .•··.. .. ,ri8.1 !( ... captures Ol' internally convertS. The two ·methode: in general use. that · '.·· :: .. · . Ji~tia£y ~he glven r~qubeme1lta· are gal!t cotmtlag using rather elaborate grid· , . ~:· ... ,.;. <. c~a~Pbers attd proportional techniqu~s., or scint!Uatton ~ouQting. Contrary (, .~:).,·.·' .:. t~ curr~t conceptions,. rel,atively hip-resohttion .scin_tUlation sp.ectroseopy t •. , • ~·u.siilg single pb~tomuJ.tipliers not <m.ly .la featdble forth~ region of.mterest. ~( .· :, . · · · .. : ::bdt can .wttb <:a.re be made t.o give ~xtr~mely low .badtgrounde ae well •. The · •. .;.,. . ' .. _ ~· ~-·(· .. • en4 product ts dettnttely superior to exiatlq gae eountera in backgrou.n4. ~nd ' . operationall.lWity. ~- ' -. THE. CCtiNTI:l\ . . . -,;: . . The counti~g head as 4estlue4 for tb:e p·vpoaes of our i~vestigation . . . . (Fig. 1) is an aluminum c:up which tits ove.r the facu&of the photomultiplier a~d 'into wh.ich are <::emented the gamma windc>w of ;0; s-mu z ~s aluutinurn. the' . *Research. sponeor.ed by the Oiftce of Naval Research and the. Atomt~ Eilel"gy Commission .. 1Hobson, Hubbs, Nierenberg. Silsbee, and Sunderland •. to be published in the .Physteal Review. .; . · i. . i . : . ~ .. UCRL·3434. ery$tal ..... o •. 2$ by 0. ~inch by liJlm-•tm·d the quartz light windQw •. Care i·s . taken to 'prevent a film of the cement, Wyva Wax, from covering either fa.ce of the scintillator. The gamm·a .. window tr~nsrnteelon is appJ'_ox1mately.90!1/o ;. f~r rubi-dium K x-rays; thln•fUril te~h1dquea mlsh.t well be u•ed to extend the . . . useful lower limit of operation to l kev. . ' . . ' . Sodium iodide crystals. at~ purch.aed ·in larg~ bloc:ks 'aad epllt to size ln a dry box with relative hurnldjty leas tban. s~~~ at l0° c. (:leavage• are n1ade by·delivel'ing a 'light blo~ to ·a razot' blade lying along a crystal plane, and ac.: ceptable fragments with no sip ·of fra'cture or diac:oloration al'e imtnediatel y ·sealed between the two w\ndows tc prevent ·surface· decomposittoJJ. · -Phototn·ultiplier ~bee .at~ selected irom tbe large numbet of tub~-~ , .acqut~ed by tb~'Radiation ~aboratory (-B~u.·keh~y). tnit~lly only 'ssl9'• wel'e flV&Uable. Perhaps one t•be in a thousand would at that time mee~ the require•. nu!n:ts .of le~s than one dark•curr~nt ~·e per miD.ute a~ve a pulse height · eqQ.iv~lent to .5-kev gamma• ln Nal. . The aecepta#ce factor (o~ the new Du.mont · ·.~6292•• doe~~ howev~r-•at least for _6ome l9t ... •ruti as. high as otle tUbe·in .. twenty •. Tb,e common de~omin&tor of ttlbes so. selected is a very large ampli-fication .for a given dynode voltage and piee"mably a relatively high, photo-. . ' ~ cathode conversion efficlen.ey •. The relative dark-current rate ie very nearly . . . . ~ independent of dynode voltage over the normal ~eglon o£ operation of the tubes. High voltage curing o£ the ph,o~OJll.ultf.plie:r.e .leads to no improvement of the . . . noise figure. '·, , CQuntf:aa is perfor-me<l:wlth'stan.da.rd Radiation Laboratory preamplifiers ·and si~gle-channel dtUere~tlal all~yzerc. The only etabUizati.Qn used is that - . . . . ·, .. of th$ analy~erand a Sorenson regilla.tor whic.h l$ ~ae<l t$ supply 110-~ ~e. The counter window is. cust9matily,.aet_'to .accept at least·CJO% of the x .. ray line~ which for 15-kev.x-rays ree~~s tn a 100% wbtdo~.· t. e.' from ~e·half t(; one and . cme-hatf of the peak ceilter •. Only a SOfa window is required to achieve the same . . results above 50 kev. tlfider aue)l adjuatmente ae tbla; small drifts in window width and height contribute a ttegligible change i.e co~ter efflcl•cy and back-ground. a factot of paramount lmportall~e £~ counting periocls which sometimes are as long a• three mo'ftth~~ The counters are shu~· down only after a counter . electronic: a failure. whteh occurs in a mean tim~ of about four months. ,·, -, . ; ,. 1: { ··. l . ';' ~ . •' . ;._. .. UCRL ... 3434 The counter h~4d ts ~hlelded with a atagge~ system, with concentric . . . . . I . . . . . ·· eyl~ric~ geometry and us.~g Z. 5 inchee ·of lea:d,. l/8 lnc:h braes, l/4 t:nch i:roa, ~~dl/8lneh or Qlor~ Qlumin~m. -Fo~ w.bulow eetti111;g£1 abOve, the counter .' b~kgr.ound.ln· ·the ahiel.d le O'f:le cou,n,t per ~~nute or lees for all e11ergy settings b~~een. s· kev and iO.O kev.; M:htttnilm ~ackgte>tt.nd occ:u.s in the netghborh~od ·of .40. k~v, wh~re it- is typ:l~ally _o, 35: crount per tninute. : Co~ter backgroun~ ou~side the shield ts ·approxl.tn~tely $count& per minute. lntegtal settings of . · th~ counter i~ Ute shield ~d.wf,th a .threshold cot~espondiftg to 3 to 5 kev res\llt .~n fiPP~~xima.tel.Y $ <;/~ baekgropd for _a contigu,,tion lti·'which· all t4 mesons, . ~ . . . . . low-ettergy gamma raya, ·and ~~d\um.,.energy e1·•Ctl"On8 are detect•d with. unit . . ·. ·.·· -·· ... · .. · .. '· .. . . ', -~ . . eUici~ncy.- The tntesra1 conti'ib~tion ~~ d'-'rk;-curreat pulses to eounter ba~k-. ' . .·· , .. ·. . . ' .·. . ·... . .·... ·4 . . . . . . . . . grottnd i~, lot a typical u~lt,· appro:dm•t~ly 10 exp ( :..~;. S kev) counts per minute betwee1l l and to lc:ev • . . ·,, . ,. -' . ._, • J, •'. \I .~ .. . ,·:; ... ' ' . · ·UCR.L-34M LEOsNDS 1'01\ FIGtJ~ES .. J"'ig. •~ ··J.)etaU ot. sctn:ttilatton head. , . ·F·ig·. Z •. · .. PW.se..:h~~ght cUet:rl~tlou of rubidiutn K x:.o.rayl. Tlt.e low-energ}r.peak e , . - . • - • is dark. current. ,....; ' '•. i ·.•: .,1'' ~' ' I .. • -6- UCRL-3434 PHOTOMULTIPLIER TUBE- No! (TI} ASSEMBLY -I I ! I ! I I I I I 1 I L-_-~~-:::.-:.J I I I~ I I~ I I I I I 1;2 mil. AI / I I I I I I I I I I L ___ $,042---J I I an.~: ~lllY..\I't,~ I I 1 I I SPRING LOADED BALL BEARING TO HOLD BUTTON BRASS HOLDER '--------'· .. r-., r-1 I I I I l I I 1 J EDGE SIDE TOP BOTTOM Fig. l ,, . . .. ..... l -7- UCRL-3434 1'-TRACE OF 15 Kev X-RAY LINE rf' ~. v ~ ~ / ~ MU-11399 Fig. 2 

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SCINTILLATION DETECTION OF VERY-LOW-ENERGY GAMMA RAYS

https://escholarship.org/uc/item/1p19918h

SCINTILLATION DETECTION OF VERY-LOW-ENERGY GAMMA RAYS

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