VNU JOURNAL OF SCIENCE, Mathematics - Physics... Some calculates of the energy and tim e resolution has been carried out and the obtained results are very good.. W ith the obtained datab
Trang 1VNU JOURNAL OF SCIENCE, Mathematics - Physics T XVIII, No3 - 2002
S O M E R E S U L T S O F I N T E R F A C I N G T H E 7 - 7
C O I N C I D 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 i n h Q u a n g
F a c u lty o f T echnology', V N V
N g u y e n D a n g L a m , P h a m D i n 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 c ie n c e , V N V
1 I n t r o d u c t io n
T h e c o n s tru c tio n o f th e s p e c tro m e te r b a se d o n S A C P m e th o d (S u rm n a tio n o f A m
p litu d e s o f c o in cid in g of p u lses) h a s lead to th e n eed o f th e in te rfa c e c a rd to ex ch an g e d a ta wit h c o m p u te r T h e in te rfa c e c a rd h a s b e e n co m p le ted at t he fa c u lty o f technology V iet
n a m N a tio n a l U n iversity H an o i W ith sim p le desig n, th e c a rd w o rked co m p le tely s ta b ility
in th e long w ork p e rio d M any m e a su rin g e x p e rim e n ts w ith th is c a r d h av e b een do n e a t
D alat n u c lea r re se a rc h I n s titu te P ro c e ssin g in d e p e n d e n tly , th e re s u lts o f e x p e rim e n ts at
H an o i a n d D u b n a p o in te d out th e g o o d o p e ra tio n o f th e s p e c tro m e te r a n d th e in terface card
2 O v e r v ie w
T h e e x p e rim e n ta l re se a rc h o i l th e n u c le a r s tr u c tu r e tru th fu lly is m e asu rin g (by th e different m e th o d s ) som e p a ra m e te rs su ch a s cro ss-sectio n , e n e rg y o f th e e x cited s ta te s ,
p ro b a b ility o f th e tra n s itio n s b e tw ee n th e e x c ite d s ta te s F ro m th e m e a s u rin g p a ra m e te rs
it is p ossible c a lc u la te q u a n tu m p a ra 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 a se s to e s tim a te , to c o rre c t a n d to c o m p le te th e n u c le a r th e o ry a n d th e o th e r a p p lic a tio n s
o f technology
T h e s tu d ie s call b e c a rrie d o u t o n th e e q u ip m e n t su ch a s th e re a c to r, accelerato r
G enerally, th e layout, of th e e x p e rim e n t is show ed o n F ig l
d Q
1«
- ► - ► - ►
In c id e n t b eam
T a rg e t
Fig 1. S tu d y in g n u c le a r s tr u c tu r e by th e n u c le a r re a c tio n s
T y p e s e t b y ^ A / j iS - T f e X
CỈƠ
d n
57
Trang 258 C h u D u c T r i n h, N g u y e n V i n h Q u a n g
T h e p o ssib ility o f th e ga m m a -ra y d eca y o f th e n u clei (b e in g s h o t by p a rticle b ea m
o f th e accelera to r or n eu tro n b e a m o f th e rea c to r) is th e h ig h est For th e reason, th e gam m a sp e c tr o m e te r w as u se d to o b ta in th e most, in fo r m a tio n o f th e s tu d ie d n ucleus T h e use o f th e s o lid -s ta te d e te c to r s w ith h ig h -en er g y r e so lu tio n a n d h ig h s p e e d en h a n ced th e accu racy o f th e m easu rin g.
H ow ever, th e effects su ch as th e C o m p to n -s c a tte r in g , e le c tio n -p o s itio n pair form a tio n in th e in tera ctio n o f g a m m a ray w it h d e te c to r h a d a b a d effect o n the ra d ia tiv e
sp ectru m an d red u ced th e a b ility o f o b ta in in g in fo rm a tio n
T h e u se o f th e sp ec tro m eter w ith o p p o sin g C o m p to n -s c a tte r in g p e r m it o f red u cin g 30% o f th e b ack grou n d g e n er a te d by th e C o m p to n -sc a tte r in g In order to reduce co m
p lete ly th e C o m p to n b ack grou n d, th e m e th o d o f s u m m a tio n o f a m p litu d e s o f coin cid en ce
p u lses m u st be u sed T oday, th ere is o n ly su ch sp e c tr o m e te r a t J IN R ( th e Join t In stitu te for N u clea r R esearch, D u b n a ) P rom th e r e su lts o b ta in e d by th e u se o f th e sy ste m , the
q u a n tity o f th e u sefu l in fo rm a tio n in crea sed m a n y tim e s T h e re su lts o b ta in e d by the oth er m e th o d are a lso th e sa m e in th e en erg y reg io n o f 0 to 8 M ev.
I n V ie tn a m
T he nuclcar reaction studies are carricd out at two centers:
- O il th e accelera to r o f th e n u clear cen ter, p h y sic in s titu te , T h e N a tio n a l Science
an d T ech n o lo g y center.
- At th e Dalat, nuclear R esearch I n s t itu t e w ith th e te s t s o n th e n eu tro n b ea m to define th e re a c tiv e cro ss-sectio n o f th e so m e n u clear is o to p e s N o w , th e m ost m od ern gain m a-ray sp e ctro m e ter s are th e m o n o -c r y sta l g a m in a -ra y s p e c tr o m e te r T h e red u ction
o f th e C o m p to n -sc a tterin g b ack g ro u n d is n o t s till o p tim a l b e c a u se o f u sin g th e p assive
m e th o d s su ch as covering, m a k in g o f c o llim a tio n b lock or th e a c tiv e m e th o d s w ith using
th e a n tico in c id en ce s y ste m a n d d e te c to r s su c h as G eiger-M tiller co u n te r or scin tilla tio n
d etecto r.
3 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
Trang 3S o m e r e s u l t s o f i n t e r f a c i n g T h e 7 — 7 c o i n c i d e n c e 59
D1 a n d 1)2 a n ' s e m ic o 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 I X ’l a n d A D C 2 un', th e IK a n a lo g to d ig ita l c o n v e rte rs o f successive a p p ro x im a tio n
T h e y w ere m a n u fa c tu re d a t D alat n u c lea r R esearch I n s titu te
F ro m 1996, I ho ideas o f e x a m in in g a n d c o n s tru c tin g th e s y s te m o f S A C P to use th e
n e u tro n b e a m at t ho I )a la t n u c le a r re a c to r h a s b e e n c a rrie d o u t U p to now , a fte r m an y o f test ing a n d e x a m in in g th e first p e rio d o f b u ild in g sy ste m h a s b e e n c o m p le te d T h e second
p e rio d o f u sin g t h e sy ste m t o re se a rc h th e n u c le a r s tru c tu re o n th e n e u tro n b e a m h as b een
s ta r te d T h e sch em a o f t h e s y s te m is o n F ig 2
T h e fast a n d slow co in cid en ce b lo cks w ere m a d e a t physic F aculty, N a tu ra l Sci
e n ces In s titu te T h e in te rfa c e c a rd w as m a d e a t F a c u lty o f T echnology, Viet n a m N a tio n al
U niversity, H anoi
O p e r a t i o n a l p r i n c i p l e o f t h e s y s t e m i s f o l l o w e d
T h e ta rg e t nuclei c a p tu r e d t h e rm a l n e u tro n lives ill th e e x c ite d s ta t e s h o rtly (1 0 “ 17 — 10“ s) a n d it will decay b y cascad e T w o so lid -s ta te d e te c to rs c a p tu r e p a irs o f g a m m a
T h e signals from Ỉ he tim e o u tp u ts o f th e d e te c to rs a re led to th e fa s t am p lifiers a n d th e
d is c 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 t h a t tim e , th e signals from th e a m p litu d e o u tp u ts OÍ th e tw o d e te c to rs a re also le d to th e s p c c lru m am plifiers Ill
t h e case o f tw o tim e signals b e in g co in cid en t, th e re is a pu lse a t o u tp u t o f th e coincidence block T h e p ulse will e n a b le th e A D C s to o p e ra te
R ise slope o f th e p u ls e s also hav e d u ty o f e ra sin g th e d a t a o f th e last conversion if
th e c o m p u te r d id not tak e th e m A fter c o n v e rtin g tw o p u lses to d ig ita l fo rm , th e A D C s will g e n e ra te th e sig n al o f ” D a ta re a d y ” to c o m p u te r to se n d d a ta
A fte r receiv in g d a ta , P C w ill g e n e ra te a c o m m a n d to e ra se th e d a t a in tw o A D C s
a n d co n tin u es th e new cycle
T h e in fo rm a tio n w as s to re d in P C u n d e r form o f a tw o -d im en sio n m a trix E \ (n )
a n d E2(rc) E l (n ) a n d E2(71) a re th e d ig ita l a m p litu d e o f th e p u lses o f d e te c to r 1 a n d
d e te c to r 2 II is th e o rd in a l n u m b e r o f th e coincident fa c t c o u n te d from th e s ta r t lim e
T h u s , th e in te rfa c e c ard h a s d u ty o f in fo rm in g tw o A D C ’s d a ta re a d y , talking d a ta to P C
a n d g e n e ra tin g th e c o m m a n d to erase d a ta in tw o A D C ’s buffer
T h e in te rfa c e c a rd is c o m p le te d from IC s-8255 T h e m e a s u rin g re s u lts w ith source
C06O a re show ed in Fig 3
'Ả ị.-ỉiịĩ.
ỉẫm
p ^ ° * <v«r A* /
i s p p 1
11V A w * vrrr* TT*»
68 1 3 5 2 0 2 2 6 9 3 3 6 4 0 3 4 7 0 5 3 7 6 0 4 6 7 1 7 3 8 8 0 5 8 7 2
3UÜ
2 5 0
*00
1 5 0
100
5 0
0
S e r i e s I
F ig S T h e p a t t e r n o f s p e c tr a C o ° o b ta in e d by th e in te rfa c e
Trang 460 C h u D u c T r i n h , N g u y e n V i n h Q u a n g
From Fig.3, it is possible to say th a t the system operates very well; the C o 60
gam m a sp ectru m of each detector is completely like w ith th a t of m ono-crystal gamma ray spectrom eter T he above results m ean th a t the address decode, the d a ta transm ission are good and stability Some calculates of the energy and tim e resolution has been carried out and the obtained results are very good.
W ith the obtained database and after the processing, the sum m ation and differential spectra of source CoC)0 are given in Fig.4.
From the differential spectrum , it is possible to say th a t the C om pton-scattering background has been erased completely.
4 E s t im a ti o n o f th e in te r f a c e o p e r a tio n
From the obtained results, it is clear th a t th e system of SACP operates very well and can be used to study the nuclear structure on the neutron channel of the reactor
T he system operates effectively like the system of JIN R (the Joint In stitu te for Nuclear Research, D ubna) although it is simple.
Interface card has good ability of the inform ation transm ission Although the num ber of the m easuring fact ill a tim e unit is not much (ab o u t 100 counts p er second) b ut the tim e of one conversion is very short about 25 ịis and the transmission rate is about
In the near future, besides using the system to study the nuclear stru ctu re the system will be enhanced w ith íbiư analog inputs.
T he au th o rs would like to thank the Hanoi national University for the financial support in th is research.
R e f e r e n c e s
1 Boueva S.T et al., Physics of Elementary Particles and Atomic Nuclei, V.22, Part.
2 Boueva ST et al., Physics of Elementary Particles and Atomic Nucleif V.22, Part
3 P h a m D in h K h an g, R esea rch o n th e C a sc a d e- 7 d eca y o f th e N u c lei Y b170 and G d 158,
P h D thesis, H anoi, 1994
4 N g u y e n Vinh Q u an g, e t al., S om e R e s u lts o f th e S p e c tr o m e te r b a s e d o n S A C P
m e th o d a t D a la i an d H an oi, The articltj the N ational Coference on P hysics, 2001.
5 P h a m D in h Kharig e t al., T h e 7 — 7 co in c id en ce S p e c tr o m e te r an d te s tin g w ith ra
d io a c tiv e S ou rce C q°, Proceedings o f The N atio nal Coference on the nuclear physic,
Fig 4‘ The sum m ation and differential spectra of source C o 60
2, 1991, p 479.
6 , 1991, p 1431.
2 0 0 1