A pulse shape discriminator for an X-ray proportional counter and its application to a coincidence experiment

NUCLEAR

1N57RUMEN75

AND

ME7H0D5

96 (1971) 317-323;

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N0R7H-H0LLAND

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A P U L 5 E 5 H A P E D15CR1M1NA70R F 0 R AN X-RAY P R 0 P 0 R 7 1 0 N A L

C0UN7ER AND 175 APPL1CA710N 7 0 A C01NC1DENCE EXPER1MEN7 Y. 1 5 0 2 U M 1 and 5. 1 5 0 2 U M 1 *

Rad10150t0pe Re5earch Center, Ky0t0 Un1ver51ty, Ky0t0, Japan Rece1ved 25 May 1971 A pu15e 5hape d15cr1m1nat10n 5y5tem ha5 6een deve10ped f0r an X-ray pr0p0rt10na1 c0unter t0 reduce the 6ack9r0und cau5ed 6y h19h ener9y rad1at10n5, 6y the u5e 0 f a m0d1f1ed t1me-t0-pu15ehe19ht c0nverter. 7e5t mea5urement5 w1th ar90n f111ed c0unter5 have 5h0wn that the 5y5tem 15 at 1ea5t 90% effect1ve 1n reduc1n9 the 6ack9r0und 1n the ener9y ran9e 6-15 keV, wh11e m0re than 9:;% 0f a11 the X.ray 519na15 can 6e accepted. Even 1n the

20-35 keV re910n, rea50na61y 900d re5u1t5 f0r the 6ack9r0und reduct10n and the X-ray acceptance have a150 6een 06ta1ned. 7 h e techn14ue ha5 6een 5ucce55fu11y app11ed t0 the c01nc1dence exper1ment w1th tw0 pr0p0rt10na1 c0unter5 1n 0rder t0 e11m1nate fa15e c01nc1dence5 due t0 unfav0ura61e h19h ener9y rad1at10n5 pa551n9 thr0u9h 60th c0unter5.

1,, 1ntr0duct10n

Much 10n9er 10n15at10n track5 91ve the r15e t1me 0f 0utput pu15e5 fr0m 9amma ray5 t0 6e much 510wer than th05e 0f X-ray 519na15. Math1e50n and 5anf0rd 1) f1r5t 5ucce55fu11y app11ed the r15e t1me d15cr1m1nat10n t0 reduct10n 0f the c05m1c ray 6ack9r0und 1n a pr0p0rt10na1 c0unter 6y reject1n9 the pu15e5 w1th 510wer r15e t1me5 than th05e 0f X-ray 519na15. 7hey c0u1d then e11m1nate a60ut 90% 0f 6ack9r0und pu15e5 fa111n9 1n the X-ray re910n, 6ut w1th c0n51dera61y 1055 0f X-ray 519na15. 51m11ar meth0d5 0f 6ack9r0und reject10n have 6een deve10ped

A pr0p0rt10na1 c0unter ha5 fre4uent1y 6een u5ed t0 detect 50ft X ray5, 6ecau5e 1t 15 ea5y t0 fa6r1cate a dev1ce w1th fav0ura61e 9e0metry, c0mparat1ve1y 1ar9e detect10n eff1c1ency and fa1r1y 900d ener9y re501ut10n. H0wever, when X ray5 0f very 10w 1nten51ty fr0m a rad10act1ve 50urce are detected 6y a pr0p0rt10na1 c0unter, 5er10u5 tr0u61e5 are met 6y h19h 1nten5e 6ack9r0und5 1n the X-ray re910n due t0 9amma ray5 fr0m the 50urce t0 6e 5tud1ed and, 1n 50me ca5e5, t0 c05m1c ray5 and natura1 9amma ray5. When h19h ener9y 9amma ray5 1nteract w1th c0unter 9a5 0r the wa11 mater1a1 0f the c0unter, ener9et1c e1ectr0n5 are pr0duced 6y the C0mpt0n effect 0r ph0t0e1ectr1c effect. 51nce a 1 MeV e1ectr0n dep051t5 a60ut 2 keV 0f ener9y per cm 1n ar90n 9a5 0f 0ne atm05phere, the ener9et1c e1ectr0n5 fr0m the 1nc1dent 9amma ray5 105e 0n1y a few keV 0f ener9y 1n the c0unter, hav1n9 10n15at10n track5 0f the 0rder 0f a few cm 1en9th. Re5u1tant 0utput 519na15 fr0m the 9amma ray5 c0rre5p0nd 1n ener9y t0 the K X-ray re910n 0f 119ht e1ement5. 7he5e 519na15 a1way5 c0ntr16ute t0 an X-ray mea5urement a5 the n0n-X-ray 6ack9r0und. A150 1n the ca5e where h19h ener9y char9ed part1c1e5 5uch a5 c05m1c ray5 1nteract d1rect1y w1th the c0unter 9a5, the 0utput 519na15 fr0m the c0unter are a1m05t 5ame a5 th05e 0f the h19h ener9y 9amma ray5. 0 n the w]~01e, 50ft X ray5 105e the1r wh01e ener91e5 1n the c0unter 6y pr0duc1n9 ph0t0e1ectr0n5, 0f wh1ch the 10n15at10n track5 are ne9119161y 5ma11 1n c0mpar150n w1th th05e 0f ener9et1c e1ectr0n5 fr0m the 9amma ray5. * N0w at 5em1c0nduct0r Re5earch La60rat0ry, 1La60rat0r1e5 Ltd., Hy090-ku, K06e, Japan.

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6y many 0ther w0rker52-5), and ma1n1y app11ed t0 X-ray a5tr0n0my exper1ment5 u51n9 1ar9e v01ume pr0p0rt10na1 c0unter53•6).

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7he 6a515 f0r the d15cr1m1nat10n 6etween X ray5 and n0n-X-ray 6ack9r0und event5 ex15t5 1n a d1fference 1n the r15e t1me5 6etween the c0rre5p0nd1n9 0utput 519na15 fr0m a pr0p0rt10na1 c0unter. 1n 0rder t0 06ta1n the 1nf0rmat10n 0n the r15e t1me5 0f the 0utput pu15e5, 61p01ar pu15e5 w1th w1dth5 depend1n9 0n the r15e t1me5 are u5ua11y pr0duced 6y the d0u61e R C d1fferent1at10n2•4). H0wever, a5 1nd1cated 6y 50me w0rker57•8), th15 meth0d cr1t1ca11y depend5 0n a 5e1ect10n 0f the d1fferent1at10n t1me c0n5tant5. 1n the pre5ent c1rcu1t wa5 emp10yed the attenuat10n-5u6tract10n techn14ue, wh1ch ha5 u5ua11y 6een u5ed 1n the 1ead1n9-ed9e t1m1n9 p1ck0ff 6y the c0n5tant fract10n 0f the pu15e he19ht tr199er9). 0 u r c1rcu1t 15 rather 51mp1e and d0e5 n0t need cr1t1ca1 adju5tment5.

A5 w1de a5 p055161e an ener9y ran9e and a5 5ma11 a5 p055161e 1055 0 f X ray5 5h0u1d 6e re4u1red, when the

r15e t1me d15cr1m1nat10n 15 app11ed t0 the 6ack9r0und reduct10n 1n the w0rk c0ncerned w1th 50ft X-ray mea5urement5. 7he pre5ent pu15e 5hape d15cr1m1nat0r ha5 6een deve10ped t0 fu1f11 th15 re4u1rement. 0 u r dev1ce wa5 f1r5t app11ed t0 the c01nc1dence mea5urement 6etween X ray5 and 10w ener9y e1ectr0n5 u51n9 tw0 pr0p0rt10na1 c0unter5 w1th re1at1ve1y 1ar9e v01ume5 1n 0rder t0 e11m1nate fa15e c01nc1dence5, wh1ch were cau5ed 6y h19h ener9y rad1at10n5 fr0m the natura1 0r191n5. We rep0rt here 1n deta11 0ur 1mpr0ved pu15e 5hape d15cr1m1nat0r and 1t5 app11cat10n 1n the c01nc1dence exper1ment w1th tw0 pr0p0rt10na1 c0unter5.

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7 0 111u5trate the pr1nc1p1e 0f the 0perat10n, a 51mp11f1ed 610ck d1a9ram 0f the c1rcu1t and wave f0rm5 at f1ve c0n5ecut1ve 5ta9e5 1n the c1rcu1t are d15p1ayed 1n f19. 1. A 519na1 fr0m the preamp11f1er 15 de1ayed 6y a t1me 1nterva1 td, wh1ch 15 u5ua11y 5e1ected 1ar9er than the r15e t1me 0f an 1nput pu15e, wh11e th15 519na1 fed t0 an attenuat0r 15 attenuated 6y a fact0r K. Feed1n9 the5e tw0 519na15 t0 a d1fferent1a1 amp11f1er, a 519na1 w1th a wave f0rm a5 5h0wn 6y a curve d 15 06ta1ned. 7hen, 6y the u5e 0f a tunne1 d10de d15cr1m1nat0r a 54uare wave w1th w1dth near1y e4ua1 t0 that 0fthe 1nput 519na1 15 06ta1ned. 7he w1dth 0f th15 0utput 519na1 15 c0nverted t0 an amp11tude 0f the tr1an91e wave 6y a t1met0-amp11tude c0nverter, a5 5h0wn 1n the f19ure. 2.2. C1RCU17 C0NF16URA710N 1n f19. 2 15 5h0Wn a C0mp1ete d1a9ram 0f the pre5ent r15e-t1me-t0-pU15e-he19ht C0nVerter, ma1n1y C0n515t5 0f f0Ur 5ta9e5; a 5ta9e f0r attenuat10n and de1ay 0f 1npUt pU15e5, a d1fferent1a1 amp11f1er, a tunne1 d10de d15cr1rn1nat0r and a t1me-t0-amp11tude c0nverter. A11 5ta9e5 are dc-c0up1ed t0 av01d the 6a5e 11ne 5h1ft cau5ed 6y h19h c0unt1n9 rate. An 1nput 519na1 15 attenuated t0 45% 0f 1t5 1n1t1a1 amp11tude 6y R1 and R2. 7hr0u9h an0ther r0ute, the 5ame 519na1 15 de1ayed 6y 120 n5 6y D L w1th attenuat10n 0f 50% 6y R3 and R4. 7w0 519na15 fr0m th15 5ta9e are fed t0 the d1fferent1a1 amp11f1er c0mp05ed 0f Q1-Q3. A 5et 0f tran515t0r5 Q1 and Q2 wa5 carefu11y 5e1ected t0 c0mpen5ate each 0ther f0r the1r therma1 dr1ft5. Q3 5erve5 a5 a h19h 1rnpedance c0n5tant current 50urce f0r Q1 and Q2. A 5111c0n d10de D1 15 u5ed t0 c0mpen5ate f0r a temperature var1at10n 1n the em1tter-6a5e v01ta9e. 7he 1nput dc-v01ta9e can 6e adju5ted t0 6e 2er0 6y a var1a61e re515t0r VR1. A current 5w1tch 15 c0mp05ed 0f Q4 and Q5 wh1ch n0rma11y c0nduct current5 0f 5 mA. 51nce m05t 0f the c011ect0r current 0f Q4 pa55e5 thr0u9h R6, the

319

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tunne1 d10de 7 D 15 n0rma11y 1n a 10w v01ta9e 5tate. When a ne9at1ve p0rt10n 0f a 61p01ar 519na1 appear5 at the c011ect0r 0f Q1, the c011ect0r current 0f Q4 1ncrea5e5 wh11e that 0f Q5 decrea5e5. 7h15 7 D 15 dr1ven t0 a h19h v01ta9e 5tate 6y a current m0re than 2 mA fr0m Q4. 7he m0ment the 1nput 61p01ar pu15e exceed5 the 2er0 1eve1, the 7 D return5 t0 a 10w v01ta9e 5tate 6ecau5e the current fr0m Q4 t0 the 7 D decrea5e5 6e10w 0.4 mA. 7he current fr0m Q4 can 6e adju5ted 6y VR2 and VR3. A w1dth 0fthe 0utput pu15e fr0m the 7 D 15 c0nverted t0 a pu15e he19ht 6y a t1me-t0-amp11tude c0nverter c0mp05ed 0f Q6-Q1 1.7w0 pa1r5 0f tran515t0r5 (Q6, Q7 and Q8, Q9) c0n5t1tute tw0 5et5 0f current 5w1tche5, wh11e a pa1r 0f c0mp11mentary tran515t0r5 Q10 and Q11 c0n5t1tute5 a c0n5tant current 50urce. 7he current fr0m Q10 can 6e adju5ted 6y a var1a61e re515t0r VR5. 7emperature dependence 0f the em1tter-6a5e v01ta9e 0f Q10 15 c0mpen5ated 6y Q11. 51nce Q8 and D2 are n0rma11y 0n, Q8 c0nduct5 the current /1+12 where 1t and /•2 are c0n5tant current5 fr0m Q10 and D2, re5pect1ve1y. When Q8 and D2 are turned 0ff 6y tr199er1n9 the 7 D t0 the h19h v01ta9e 5tate, the current 15 1ncrea5e5 the v01ta9e 0f a c0nden5er C1 w1th a c0n5tant 5peed 1t/C, where C 15 a capac1tance 0f th15 1nte9ra1 c0nden5er. When the 7 D return5 t0 the 10w v01ta9e 5tate, Q8 15 turned 0n and c0nduct5 the current 11 +/2. 7hen the v01ta9e acr055 C1 decrea5e5 w1th a c0n5tant 5peed [2/C. 7h15 5peed can 6e chan9ed 6y VR4. A var1a61e re515t0r VR6 15 f0r the 0ff5et adju5tment 0f current 5w1che5 Q6-Q9. Q12 15 u5ed a5 an em1tter f0110wer. C0mp11mentary tran515t0r5 Q13 and Q14 c0n5t1tute a 10w 1mpedance 0utput 5ta9e. Leve1 5h1ft d10:1e5 D4-D6 c0ntr16ute t0 the temperature c0mpen5at10n f0r Q13 and Q14. 3. Perf0rmance

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exper1menta1 arran9ement 5h0wn 5chemat1ca11y 1n f19. 3. 8 0 t h c0unter5 exam1ned were a1um1n1um cy11nder5; 0ne wa5 0f 30 cm effect1ve 1en9th w1th 5 cm 1nner d1a. and an0ther wa5 0f 5ame 1en9th 6ut w1th a 1ar9er 1nner d1a. 0f 10 cm. A hard-drawn tun95ten w1re 0f 21 /~m 1n d1a. wa5 u5ed a5 the center w1re. 7he5e c0unter5 were 9a5-f10w type. A c0mmerc1a1 9a5 m1xture 0f 90% ar90n and 10% methane at 0ne atm05phere wa5 pa55ed thr0u9h at a c0n5tant f10w rate 0 f a 6 0 u t 3 cm3/m1n. 80th c0unter5 were pr0v1ded w1th my1ar w1nd0w5 (1 m9/cm 2 th1ck and a60ut 2.5 cm d1a.), c0ated w1th a60ut 200 A th1ck a1um1n1um 6y evap01at10n t0 make 1t e1ectr1ca11y c0nduct1ve. 7 h r 0 u 9 h 5uch a very th1n w1nd0w, ph0t0n5 w1th ener91e5 m0re than 3 keV can enter the c0unter w1th0ut apprec1a61e a650rpt10n. 7 h e ener9y re501ut10n5 0f the5e c0unter5 (5 cm and 10 cm 1nner d1a.) f0r 5.9 keV M n K X ray5 fr0m 55Fe were a60ut 16% and 17%, re5pect1ve1y. 0 u t p u t 519na15 fr0m the char9e 5en51t1ve preamp11f1er were fed t0 tw0 5eparated channe15; 0ne wa5 u5ed f0r the pu15e he19ht ana1y515 wh11e an0ther wa5 f0r the r15e t1me ana1y515. 1n the ••ener9y channe1••, the pu15e5 were further amp11f1ed 6y an act1ve f11ter amp11f1er and fed t0 the 51n91e channe1 ana1y5er (5.C.A.), wh1ch 5erve5 t0 5e1ect the 519na15 0f appr0pr1ate ener91e5. 1n the ••r15e t1me channe1••, the pu15e5 were fed t0 the r15e-t1me-t0-pu15e-he19ht c0nverter exp1a1ned 1n the preced1n9 5ect10n. 8 y th15 c1rcu1t, the r15e t1me5

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0f the pu15e5 fr0m the preamp11f1er were c0nverted 1nt0 a pu15e he19ht 5pectrum. 7he 5.C.A. 1n the r15e t1me channe1 wa5 u5ed t0 5e1ect the appr0pr1ate r15e t1me 519na15 0n1y due t0 X ray5. 7 h e 0utput pu15e5 fr0m the 510w c01nc1dence c1rcu1t tr199ered a 400-channe1 ana1y5er, 1n wh1ch 0n1y X-ray 519na15 were rec0rded. 1n 0rder t0 exam1ne a mer1t 0f the pu15e 5hape d15cr1m1nat10n 5y5tem (P.5.D.), the f0110w1n9 tw0 4uant1t1e5 were mea5ured: a 6ack9r0und reject10n eff1c1ency R8(E) def1ned a5 a rat10 0f 6ack9r0und 519na15 e11m1nated 6y the P.5.D. t0 the t0ta1 6ack9r0und at the ener9y E, and a X-ray acceptance eff1c1ency A x ( E ) def1ned a5 a rat10 0f the n u m 6 e r 0f X-ray 519na15 accepted 6y the P.5.D. t0 the n u m 6 e r 0f X ray5 detected 6y the c0unter. 7 h e 1.17 and 1.33 MeV 9 a m m a ray5 fr0m 6°C0 and 662 keV 9 a m m a ray5 fr0m 137C5 were u5ed a5 6ack9r0und 50urce5. 7he eff1c1ency A x ( E ) wa5 mea5ured u51n9 the f0110w1n9 X ray5 and 10w ener9y 9 a m m a r a y 5 : 5 . 9 keV Mn K X ray5 fr0m 55Fe, 8.1 keV Cu K X ray5 fr0m 652n, 10.5 keV A5 K X ray5 fr0m 755e, 14.4keV 9 a m m a ray5 fr0m 57C0, 22.2 keV A9 K X ray5 fr0m 1°9Cd and 32.2 keV 8 a K X ray5 fr0m ~73C5. An an0de v01ta9e 1700 V wa5 app11ed t0 the 5ma11 c0unter t0 reta1n 11near1ty f0r the ener9y ran9e fr0m 2er0 t0 a60ut 20 keV. 7 h e 065erved r15e t1me 5pectra f0r ph0t0n5 0f var10u5 ener91e5 are pre5ented 1n f19. 4. 7 h e 8.1 keV X ray5 fr0m 652n exh161t 11tt1e r15e t1me

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F19. 4. R15e t1me 5pectra 0f var10u5 ener9y ph0t0n5 06ta1ned fr0m the 5ma11 c0unter. 7he h0r120nta1 5ca1e 15 re1ated t0 r15e t1me. 7he 1ar9er channe1 num6er 1nd1cate5 the 510wer r15e t1me. 1n 0rder t0 06ta1n the 5pectrum d 0f 14.4 keV 9amma ray5, 6.4 keV Fe K X ray5 fr0m 57C0 were reduced 6y an a650r6er 0f a60ut 0.5 mm th1ck a1um1n1umf011.A 5ma11peak at 132 channe11n curve d 15cau5ed 6y the 6.4 keV X ray5.7he h0r120nta1 11ne1n f19. 8 1nd1cate5 the r15e t1me re910n 5e1ected 6y the 5.C.A. t0 en5ure the acceptance 0f a11 the X ray5 w1th ener91e5 6-15 keV.

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keV

F19. 5. Pu15e he19ht 5pectra 0f 9 a m m a ray5 fr0m 60C0 mea5ured 6y the 5ma11 c0unter w1th and w1th0ut the u5e 0f a pu15e 5hape d15cr1m1nat0r.

d15per510n wh11e the 9 a m m a ray5 fr0m 60C0 5h0w5 a 6r0ad d15tr16ut10n (5ee f19. 4A). 1t 15 apparent that 6y 5e1ect10n 0f an appr0pr1ate r15e t1me re910n a 1ar9e num6er 0f 6ack9r0und event5 can 6e reduced wh11e a;1m05t a11 0f the X-ray event5 are reta1ned. H0wever, a5 5h0wn 1n f19. 48, the peak p051t10n 1n the r15e t1me 5pectrum 0f 10w ener9y ph0t0n5 5119ht1y depend5 0n the1r ener91e5. 7h15 tendency, unfav0ura61e f0r perf0rmance 0f the P.5.D. 1n the w1de ener9y ran9e, 15 cau5ed ma1n1y 6y the t1me 51ew1n9 0f the 5tart 0f the 0~atput wave fr0m the tunne1 d10de d15cr1m1nat0r, depend1n9 0n the amp11tude 0f the 1nput pu15e. 1n 0rder t0 re11eve th15 pr061em 0f amp11tude dependence, we u5ed a preamp11f1er w1th 10w n015e and h19h 9a1n t0 5et a tr199er 1eve1 0f the tunne1 d10de re1at1ve1y a5 10w a5 p055161e. Neverthe1e55, we c0u1d n0t av01d the dependence 0f the 0rder 5h0wn 1n f19. 48. 1n 0rder t0 en5ure the acceptance 0f the X ray5 w1th ener91e5 fr0m 6 keV t0 15 keV, the r15e t1me 519na15 c0rre5p0nd1n9 t0 519na15 1n the channe1 ran9e fr0m 125 t0 150 wa5 5e1ected 6y the 5.C.A. 1n the r15e t1me channe1, a5 5h0wn 1n the f19ure. 7he reduct10n 1n 1nten51ty 0f a typ1ca1 9 a m m a 5pectrum fr0m 6°C0 15 d15p1ayed 1n f19. 5. 7he 6ack9r0und reject10n eff1c1enc1e5 R8(E ) mea5ured w1th 6°C0 and 137C5 and a150 the X-ray acceptance eff1c1ency A x ( E ) are 5h0wn 1n f19. 6. Accept1n9 a60ut 95% 0f X ray5 1n the 6-15 keV re910n, R8(E ) 15 m0re than 90%. 7he Rn(E) fa1r1y depend5 0n the ener9y 0f the 1nc1dent 9amma ray5: the 9 a m m a ray5 fr0m 6°C0 91ve 6etter va1ue5 0f R8(E) than th05e ray5 w1th the 10wer ener9y fr0m 137C5. 1t 5h0u1d 6e n0ted that, 1n 60th ca5e5 w1th 6°C0 and 137C5, the R~(E) decrea5e5

PR0P0R710NAL

321

C0UN7ER

6e10w 6 keV. 7he 5teep r15e 0f the R8(E) curve5 6e10w a60ut 2 keV may 6e due t0 an a6n0rma1 1ncrea5e 0f 10n15at10n 6y 50me unkn0wn effect5 1n th15 ener9y re910n. A va1ue 0f Ax(E) f0r 3 keV 15 a60ut 80%. H0wever, a pr0per 5ett1n9 0f the 5.C.A. 1n the r15e t1me channe1, A x ( E ) f0r th15 ener9y c0u1d 6e ra15ed up t0 a60ut 95%, 6ut w1th 5ma11er R8(E). 7he 6ack9r0und 519na15 due t0 c05m1c ray5 and natura1 9amma ray5 91ve ener9y and r15e t1me 5pectra very 51m11ar t0 th05e 0f the 9 a m m a ray5 fr0m 6°C0. We were a61e t0 e11m1nate the 6ack9r0und due t0 the5e natura1 rad1at10n5 w1th a1m05t the 5ame eff1c1ency a5 a60ut 1 MeV 9amma ray5. W1th the 1ar9e c0unter, we mea5ured R8(E) and Ax(E) f0r the h19her ener9y ran9e 20-35 keV. W1th an app11ed v01ta9e 0f 1650 V we ach1eved a 11near1ty f0r the ener9y ran9e 0-35 keV. 7he r15e t1me 5pectra f0r the 10w ener9y ph0t0n5 were f0und t0 6e d1fferent fr0m th05e w1th the 5ma11er c0unter; a5 5h0wn 1n f19. 7, each r15e t1me peak ha5 a 6r0ader 5pread and ha5 a c0n51dera61y 10n9 ta11 1n the 510wer r15e t1me 51de. 7h15 ta11 6ec0me5 re1at1ve1y 10n9er f0r h19her 1nc1dent ph0t0n ener9y. 7he5e unfav0ura61e re5u1t5 may 6e cau5ed 6y the e1ectr1c f1e1d 6e1n9 d1fferent fr0m the 5ma11er c0unter. W1th a 5ett1n9 0f the 5.C.A. t0 c0ver the r15e t1me peak5 f0r 22.2 keV A9 K X ray5 and 32.2 keV 8a K X ray5, a60ut 80% 0f 6ack9r0und event5 fr0m 6°C0 were e11m1nated 1n the 20-35 keV re910n wh11e m0re than 90% 0f the X ray5 were accepted. 1

1

1

J

1

1

1

100 -

j

1

1

-

~

J

1

7

~3~

-

m

80

/50

~.~.~..

40

1

0

1 2

7

•

1 4

~1--- R8(E) F0R 6AMMARAY5 FR0M

137,

1

1

1 6

1

ENER6Y.

1 8

1

1 10

1

1 12

05

~

1 J 14

keV

F19. 6. Mea5ured 6ack9r0und reject10n eff1c1ency Rr~(E) and X-ray acceptance eff1c1ency A x ( E ) . F1ve va1ue5 0f the A x ( E ) at d1fferent ener91e5 were 06ta1ned fr0m 3.0 keV e5cape peak 0f Mn K X ray5, 5.9 keV Mn K X ray5 fr0m 55Fe, 8.1 keV Cu K X ray5 fr0m 652n, 10.5 keV A5 K X ray5 fr0m 755e and 14.4 keV 9 a m m a ray5 fr0m 57C0, re5pect1ve1y. Vert1ca1 6ar5 0f A x (E)1nd1cate the err0r5 due t0 c0unt1n9 5tat15t1c5 and uncerta1nty 1n the 5hape 0f the c0nt1nu0u5 6ack9r0und under the mea5ured p h 0 t 0 n peak5.

322

Y. 1 5 0 2 U M 1 A N D 5. 1 5 0 2 U M 1

7he pre5ent mea5urement 0f R8(E) and Ax(E) 1n the 20-35 keV re910n wa5 50mewhat un5at15fact0ry, 51nce the c0unter wa5 f111ed w1th ar90n 9 a 5 . 0 t h e r rare 1

3

1

1

1

F

1

1

9a5e5 w1th h19her at0m1c num6er5 5uch a5 krypt0n and xen0n are u5ua11y u5ed t0 detect the X ray5 w1th h19her ener91e5. 7he r15e t1me d15per510n can 6e m0re 5uppre55ed 6y the u5e 0 f a 5ma11er v01ume c0unter f111ed w1th 5uch 9a5e5.

4. An app11cat10n t0 c01nc1dence exper1men1 0

Cu K X RAY5 (8.1 keV)

)

12 0

4

1

~ 6

A9 K X RAY5 (22.2 keV)

"~.~

•• JJ

0

1

70

50

90

100

120

CHANNEL NUM8ER

F19. 7. R15e t1me 5pectra 0f tw0 d1fferent X ray5 06ta1ned fr0m the 1ar9e c0unter.

x102

1

1

1

~j

1

1

14

1

A

1n c01nc1dence exper1ment5 u51n9 tw0 pr0p0rt10na1 c0unter5, fa15e c01nc1dence c0unt5 due t0 h19h ener9y rad1at10n5 pa551n9 thr0u9h 60th c0unter5 a1way5 91ve r15e t0 5er10u5 tr0u61e5. F0r the purp05e 0f reduc1n9 5uch fa15e c0unt5, a new c01nc1dence 5y5tem 1nc1ud1n9 the P.5.D. wa5 de519ned f0r the exper1ment u51n9 tw0 pr0p0rt10na1 c0unter5. 7h15 5y5tem wa5 5ucce55fu11y u5ed t0 mea5ure the K-5he11 1nterna1 10n15at10n pr06a6111ty dur1n9 6eta decay 0f63N1~°). Deta115 0fthe 5y5tem are 91ven 1n ref. 10. 7he 8.1 keV Cu K X ray5 em1tted 6y the 10n15at10n pr0ce55 wa5 detected 6y a 5ma11 c0unter, wh11e a 1ar9er c0unter wa5 u5ed f0r detect1n9 6eta part1c1e5; d1men510n5 0f 60th c0unter5 were the 5ame a5 ment10ned 1n the preced1n9 5ect10n. 1n 0rder t0 ach1eve 4 n-c0unt1n9 f0r 6eta part1c1e5, a 63N1 50UrCe Wa5 m0Unted 1n the 1ar9e C0Unter. 7he pre5ent P.5.D. 5y5tem Wa5 6U11t 1n the X-ray Channe1 0fthe C01nC1denCe 1 ~"

1

1 ~ A1rK X RAY1 1

-

1

(3.0 , e v )

1

1

8

-

12

t0

0

1

8

9

6

°

4

4

i'l .

0

20

40

60

CHANNEL NUM8ER

80

0

20

Cu K X RAY

40

60

~

80

--

100

CHANNEL NUM8ER

F19. 8. Pu15e he19ht 5pectra fr0m the 5ma11 c0unter 1n c01nc1dence w1th 519na15 fr0m the 1ar9e c0unter, w1th and w1th0ut a 63N1 50urce m0unted 1n the 1atter. A: C01nc1dence 5pectra 0f 6ack9r0und event5 due t0 natura1 9amma ray5 and c05m1c ray5 (a) w1th and (6) w1th0ut the u5e 0f a pu15e 5hape d15cr1m1nat0r. 8: C01nc1dence 5pectra 0f the ph0t0n5 fr0m 6~N1 50urce m0unted 1n the 1ar9e c0unter (a) w1th and (6) w1th0ut a pu15e 5hape d15cr1m1nat0r.

P U L 5 E 5HAPE D 1 5 C R 1 M 1 N A 7 0 R F 0 R AN X - R A Y P R 0 P 0 R 7 1 0 N A L

5y5tem 1n 0rder t0 5e1ect 0n1y 519na15 w1th the r15e t1me5 appr0pr1ate t0 the X ray5. 7h05e 519na15 5e1ected c0u1d tr199er the 9ate 0f the mu1t1channe1 ana1y5er, 6y wh1ch the X-ray 5pectrum 1n c01nc1dence w1th 6eta part1c1e5 wa5 rec0rded. 1n f19. 8A curve 6 5h0w5 the c01nc1dence 5pectrum 0f the 6ack9r0und w1th0ut the u5e 0f the P.5.D., ma1n1y cau5ed 6y the c05m1c ray5 and the natura1 9amma ray5 pa551n9 thr0u9h 60th c0unter5. C0mpar1n9 th15 w1th the data 06ta1ned w1th the P.5.D., 5h0wn 6y curve a 1n the f19ure, 1t 15 rec09n12ed that m05t 0f the 6ack9r0und c0u1d 6e e11m1nated 6y 0ur P.5.D. An X-ray c01nc1dence 5pectra mea5ured w1th a 63N1 50urce 1n5erted 1nt0 the 1ar9e c0unter are a150 5h0wn 1n f19. 88; curve a 06ta1ned 6y 0perat1n9 the P.5.D. and curve 6 06ta1ned w1th0ut 1t. A5 5h0wn 6y the curve 6, w1th0ut the u5e 0f the P.5.D. a 5ma11 X-ray peak due t0 the K-5he11 1nterna1 10n15at10n dur1n9 6eta decay 0f 63N1 (8.1 keV Cu K X ray) 15 6ur1ed c0mp1ete1y 1n the 1ar9e 6ack9r0und. 8y the u5e 0f the P.5.D. the X-ray 519na15 wa5 f0und t0 6e accepted m0re than 95% u51n9 the 5ame X ray5 fr0m 652n. H0wever, 519na15 fr0m 3.0 keV Ar K X ray5 5h0wn 6y the 5harp peak 1n the f19ure wa5 c0n51dera61y reduced 6ecau5e 0fthe re5tr1cted 5ett1n9 0fthe 5.C.A. 1n the P.5.D. 5y5tem. W1th a 6etter 5ett1n9 0f the 5.C.A., m0re than 95% 0f X-ray 519na15 ran91n9 fr0m 3 keV t0 15 keV w0u1d 6e ea511y accepted. A5 5u99e5ted 6y Camp6e114), the u5e 0f a pr0p0rt10na1 c0unter 1n the c01nc1dence exper1ment acc0mpany5 an 1nev1ta61e d15advanta9e. 7he c011ect10n t1me 0f e1ectr0n5 created 6y the f1r5t 10n15at10n 1n the c0unter 9a5 15 rather 10n9 6ecau5e 0f the 510w m06111ty 0f the e1ectr0n5. M0re0ver, the c011ect10n t1me 15

C0UN7ER

323

chan9ed 6y p051t10n, d1rect10n and 1en9th 0f the f1r5t 10n15at10n track. 7heref0re, 1n the c01nc1dence w0rk u51n9 a pr0p0rt10na1 c0unter, a 900d t1me re501ut10n 15 n0t expected. 1n fact, the t1me re501ut10n 0f the pre5ent c01nc1dence 5y5tem wa5 a60ut 1.8/~5. 5uch a p00r t1me re501ut10n a1way5 cau5e5 a 1ar9e num6er 0f the rand0m c01nc1dence5 f0r c0n51dera61y h19h c0unt1n9 rate5. 1n the pre5ent exper1ment, the 50urce 1nten51ty wa5 made very weak (a60ut 0.3/~C1) 6ecau5e 0f the 4re-c0unt1n9 9e0metry. 7he pr061em 0fthe rand0m c01nc1dence wa5 n0t 519n1f1cant, 51nce a rat10 0frand0m t0 true c01nc1dence5 wa5 f0und t0 6e a60ut 1/20. Auth0r5 expre55 the1r 51ncere thank5 t0 Pr0f. 5. 5h1m12u f0r h15 enc0ura9ement and act1ve d15cu5510n5. 7hey are a150 very 9ratefu1 t0 7. K1tahara, Y. Nakayama and R. Katan0 f0r va1ua61e adv1ce5 and he1p5 1n 5ett1n9 up the exper1menta1 e4u1pment5. Reference5 a) E. Math1e50n and P . W . 5anf0rd, Pr0c. 1ntern. 5ymp. Nuc1ear e1ectr0n1c5, Par15, 1963 (ENEA, 1964) p. 65. 2) 6 . F. 5ne111n9, Un1ted K1n9d0m At0m1c Ener9y Re5earch 6 r 0 u p Rep0rt AERE-R 5749 (1968). 8) p. 60ren5te1n and 5. M1ck1ew1c2, Rev. 5c1. 1n5tr. 39 (1968) 816. 4) j. L. Camp6e11, Nuc1. 1n5tr. and Meth. 65 (1968) 333. ~) L. L. Lewyn, Nuc1. 1n5tr. and Meth. 82 (1970) 138. 6) 8. A. C00ke, K . A . P0und5, E . A . 5teward50n and D. J. Adam5, A5tr0phy5. J. Letter5 150 (1967) L189. 7) j. M. Cutt1er, 5. 6reen6er9er and 5. 5ha1ev, Nuc1.1n5tr. and Meth. 75 (1969) 309. 8) E. Math1e50n and 7. J. Harr15, Nuc1. 1n5tr. and Meth. 88 (1970) 181. 9) D. A. 6edcke and W. J. McD0na1d, Nuc1.1n5tr. and Meth. 58 (1968) 253. 10) y . 1502um1 and 5. 5h1m12u, Phy5. Rev. C 4 (1971) 522.