VNU JOURNAL OF SCIENCE, Mathematics - Physics T XVIII, No3 - 2002 S O M E R E S U L T S O F IN T E R F A C IN G THE - C O IN C ID E N C E S P E C T R O M E T E R A N D C O M P U T E R C h u D u e T r i n h N g u y e n V in h Q u a n g F a c u lty o f Technology', V N V N g u y e n D a n g L a m , P h a m D in h K h a n g D e p a r tm e n t o f P h y s ic s, C o lleg e o f S cien ce, V N V I n tr o d u c tio n T h e c o n stru c tio n o f th e s p e c tro m e te r b a se d on S A C P m e th o d (S u rm n atio n o f A m ­ p litu d e s o f coinciding of pulses) h a s lead to th e n eed o f th e in terface c a rd to exchange d a ta wit h c o m p u te r T h e in terface c a rd h a s b e e n co m p leted at t he facu lty o f technology V iet­ n a m N a tio n a l U niversity H anoi W ith sim ple design, th e card w orked co m p letely sta b ility in th e long w ork p erio d M any m e asu rin g e x p erim en ts w ith th is c a rd have b een done a t D alat n u clear re sea rc h In s titu te P ro cessin g in d ep en d en tly , th e re su lts o f ex p erim en ts at H anoi a n d D u b n a p o in te d out th e good o p e tio n o f th e s p e c tro m e te r a n d th e in terface card O v e r v ie w T h e e x p e rim e n ta l research o i l th e n u clear s tru c tu re tru th fu lly is m easu rin g (by th e different m e th o d s ) som e p a m e te rs su ch as cross-section, en erg y o f th e excited states, p ro b a b ility of th e tra n s itio n s b etw een th e e x cited s ta te s F rom th e m e asu rin g p a m e te rs it is possible c alc u la te q u a n tu m p a m e te rs o f th e s ta te s T h e e x p e rim e n ta l re su lts a re th e b ases to e s tim a te , to co rrect a n d to c o m p lete th e n u clear th e o ry a n d th e o th e r a p p licatio n s o f technology T h e s tu d ie s call be c a rrie d o u t on th e e q u ip m e n t such a s th e re a c to r, accelerator G enerally, th e layout, of th e e x p e rim e n t is show ed on F ig l dQ CỈƠ 1« dn ► ► ► In c id e n t beam T a rg e t Fig S tu d y in g n u clear s tru c tu re by th e n u c lea r re a c tio n s T y p e s e t b y ^ A / j iS - T f e X 57 C h u D u c T r in h , N g u y e n 58 V in h Q u a n g T h e p o ssib ility o f th e gam m a-ray d eca y o f th e n u clei (b ein g sh o t by p article b eam o f th e accelerator or n eu tron b ea m o f th e reactor) is th e h ig h est For th e reason, th e gam m a sp ectro m eter w as u sed to o b ta in th e most, in fo rm a tio n o f th e stu d ie d nucleus T h e use o f th e so lid -sta te d etecto rs w ith h ig h -en erg y reso lu tio n a n d h ig h sp e e d en h an ced th e accuracy o f th e m easuring H ow ever, th e effects su ch as th e C o m p to n -sc a tte r in g , e le c tio n -p o sitio n pair form a­ tion in the in tera ctio n o f g a m m a ray w ith d etecto r h a d a b ad effect o n the rad iative sp ectru m and red u ced th e a b ility o f o b ta in in g in form ation T h e use o f th e sp ectro m eter w ith o p p o sin g C o m p to n -sca tterin g p e r m it o f red u cing 30% o f th e background g en era ted by th e C o m p to n -sca tterin g In order to reduce com ­ p letely th e C o m p to n background, th e m eth o d o f su m m a tio n o f a m p litu d e s o f coincidence p u lses m u st be used Today, there is o n ly such sp ectro m eter a t J IN R (th e Joint In stitu te for N u clear R esearch, D u b n a ) Prom th e resu lts o b ta in ed by th e u se o f th e sy stem , the q u an tity o f the u sefu l in fo rm a tio n in creased m an y tim es T h e resu lts o b ta in ed by the oth er m eth o d are also th e sa m e in th e en erg y region o f to M ev I n V ie tn a m The nuclcar reaction studies are carricd out at two centers: - O il th e accelerator o f th e n uclear cen ter, p h y sic in s titu te , T h e N a tio n a l Science and T ech n ology center - At th e Dalat, nuclear R esearch I n s titu te w ith th e te s ts o n th e n eu tron b eam to define th e rea ctiv e cro ss-sectio n o f th e so m e nuclear iso to p e s N ow , th e m ost m odern gainm a-ray sp ectro m eters are th e m o n o -cry sta l gam in a-ray sp ectro m eter T h e reduction o f the C o m p to n -sca tterin g back grou n d is n o t s till o p tim a l b eca u se o f u sin g the passive m eth o d s such as covering, m ak in g o f c o llim a tio n block or th e a ctiv e m e th o d s w ith using th e a n ticoin cid en ce sy ste m a n d d etecto rs su ch as G eiger-M tiller co u n ter or scin tillation d etector S p e c t r o m e t e r o f S u m m a t i o n o f a m p l i t u d e s o f c o i n c i d e n c e p u l s e s Fig T h e sch em a o f th e selec ted sy ste m at D a la i a fter m an y o f different te sts S o m e r e s u lts o f in te r fa c in g The — c o in c id e n c e 59 D1 a n d 1)2 a n ' sem ico n d u c to r d e te c to rs SA1 a n d SA2 a rc s p e c tru m am plifiers; A IX ’l a n d A D C un', th e IK a n alo g to d ig ita l c o n v erters o f successive a p p ro x im atio n T h e y w ere m a n u fa c tu re d a t D alat n u clear R esearch In s titu te F ro m 1996, I ho ideas o f ex am in in g a n d c o n stru c tin g th e sy ste m o f S A C P to use th e n e u tro n b e am at t ho I )a la t n u c le a r re a c to r h a s b een carrie d o u t U p to now , a fte r m any of test ing a n d ex am in in g the first p e rio d o f b u ild in g sy stem h a s b e en co m p leted T h e second p e rio d o f using t h e sy stem t o research th e n u c lea r s tru c tu re o n th e n e u tro n b e a m h as been s ta rte d T h e schem a o f t h e sy ste m is o n F ig.2 T h e fast a n d slow coincidence blocks w ere m ad e a t physic Faculty, N a tu l Sci­ ences In s titu te T h e in terface c a rd w as m ad e a t F acu lty o f Technology, Viet n am N atio n al U niversity, H anoi O p e r a tio n a l p r in c ip le o f th e s y s t e m is fo llo w e d T h e ta rg e t nuclei c a p tu re d t h e rm a l n e u tro n lives ill th e e x cited s ta te s h o rtly (1 “ 17 — s) a n d it will decay by cascade T w o so lid -sta te d e te c to rs c a p tu re p a irs of gam m a 10“ T h e signals from Ỉ he tim e o u u ts o f th e d e te c to rs are led to th e fa st am plifiers a n d the d isc rim in a to r a n d th e n 1.0 th e in p u ts o f th e coincidence block At th a t tim e , th e signals from th e a m p litu d e o u u ts OÍ th e two d e te c to rs a re also led to th e s p c c lru m am plifiers Ill t he case o f two tim e signals b e in g co in cid en t, th e re is a pulse a t o u u t o f th e coincidence block T h e pulse will en ab le th e A D C s to o p e te Rise slope o f th e p u lses also have d u ty of e sin g th e d a ta o f th e last conversion if th e c o m p u te r d id not take th e m A fter co n v ertin g tw o pu lses to d ig ita l form , th e A D C s will g en erate th e signal o f ” D a ta re a d y ” to c o m p u te r to sen d d a ta A fter receiving d a ta , P C w ill g e n e te a co m m an d to erase th e d a t a in two A D C s a n d continues th e new cycle T h e in fo rm atio n w as s to re d in P C u n d e r form of a tw o-dim ension m a trix E \ (n ) a n d E (rc) E l (n ) a n d E (71) a re th e d ig ita l a m p litu d e o f th e pu lses o f d e te c to r an d d e te c to r II is th e o rd in al n u m b e r o f th e coincident fact co u n ted from th e s ta r t lim e T h u s, th e interface card h a s d u ty of in fo rm in g two A D C ’s d a ta read y , talking d a ta to P C a n d g e n eratin g th e c o m m a n d to erase d a ta in two A D C ’s buffer T h e in terface card is c o m p le ted from IC s-8255 T h e m e a su rin g re s u lts w ith source C 06 O a re show ed in Fig 3UÜ 250 *00 150 S e r ie s I 'Ả ị.-ỉiịĩ ỉẫm 100 ^ ° *