VNIU Journal o f Science M athem atics - I’hysics 25 (2009) 231-230 Studying o f characteristic o f GEM 40P4 HPGE detector by experiment B u i V a n L o a t ' *, N g u y e n V a n Q u â n ' , L c T u a n A n h ', T r a n T h e A n h ', N g u y e n T h e N g h i a ’, N g u y e n V a n H u n g ^Hanoi V nivcrsiĩy o f Scicnces,VNU, 334 Nguyen Trai Thanh Xiian Hanoi, Vietnam InstUutc fo r Niiclcar Rcscarcỉi Daỉat, 01 Nguyen Til Luc, Dalai, Vicinam Rcccivcd N ovem ber 2009 Abstract Radioactive sourccs which used to study were the standardized radioactive o f com m on m onocncrgeĩic d ion uclide and standardized m ultiuam nia C o ^ , B a '^ \ Determination o f the absolute e íỉlc ic n c y curve and cnoruy resolulion as a function o f cneruy o f G E M P HPGe spectrom eter arc p re sen ted in this paper K cyw orils: GI'M4()IM 1IPGI: detector, relative efficiency, absolute cfilcicncy, energy resolution I n t r o d u c t io n The high purity gcrn ian iu m (llP G c ) spectrom eter is used for analysis o f environm ental sample and d e t e r m i n a t i o n o f r a d i o i s o t o p e c o n c e n t r a t i o n d u e t o Its c x c c l l c n l r c s o l u l i o n 'I'his detector has better characteristics and m ore sensitive to the detection o f impurities W hen purchasing an ỈIP G e detector, o p o r n t i n g c b a r a c t c r i ' ’ticr Guch ar> r c i i o l u l i o n , a b s o l u t e c f i i c i c n c y WCIL c u i m i i o n l y Ubcd t o c u u i p a i c different system s and to ju d g e pcrforniancc / / Ahsoĩỉiíe efu'icncy o j I!P G l' detector num ber o f counts in t h e f u l l - e n e r g y p h o t o - p c a k t o t h e t ot a l n u m b e r o f g a m m a r a y s c n i i t l c d f r o m a source and can b e determined by lorm ulal Ị-4 |; A s V c k n o w n t h a t t h e a b s o l u l c c f i i c i c n c y o f l I P G e d c t c c t o r IS t h e r a t i o o f t h e (I) w h e r e /;(/:') IS t h e a b s o l u t e d c l c c t i o n e f f i c i c n c y a t e n e r g y o f E, N IS n u m b e r o f c o u n t s i n t h e p h o t o - p e a k (net area), A is activity o f g am m a sourcc at m easurem ent time, Br is branching ratio corresponding to the energy o f /:, and ĩr is denotes the real time taken for cach successive measurement In principal, clTicicncics o f germ anium dclcclors can be estimated from published m easurements or calculations ibr detectors o f similar size, the accuracy o f results based on these values will not be m uch better than 10-20‘!o []] O ne m ajor difficulty that llie dim ensions o f these detectors are not Corresponding author loalbv@ vnu.cdu.vn 231 B I ' l.oai CÍ (ÌỈ / I 'NU Journal o f Scicncc, Mỉivmìcs - Physics 25 (2(W )) M - 232 standardized to any degree, and il is very difficult to dclcnninc prcciscly llicii active volum e (includc d e a d la yer) O n o t h e r h a n d , a b s o l u t e e lT ic ic n c y a r e d e p e n d n o t o n l y d c l e c t o r ỊM'opcrtics b u t a l s o o n th e details o f the counting geom etry (primarily the distance from the source to the detector) H ence, in s o m e c a s e vvc a l s o n e e d t o c a l c u l a t c d a b s o l u t e c i r i c i e n c y a s g e o m e t r y I ' u n c l i o n ( t h e f u n c t i o n o f t h e distance between source and dctcctor) I'urlhermore, long-term chan^cs in charuc collcclion cii'icicrncy and w indow thickness can lead lo drills in the dctcclor ciTicicncy over p eriods o f lime For these reasons, \vc must normally carry out our own periodic cfficicncy calibrations o f our g e r m a n i u m detectors To c a l c u l a l c the e n e r g y d c p c n d c n c c o f the d et e ct or e í ì ì c i c n c y , a SCI o f s e v e r a l reference gam ma sourcc w hich known nuclide activity and gam m a em ission probability is need e d to cover the energy ranges o f interest (IAEA, 1991; Sima ei al., 2001; Sima and C’a/an , 2004) If \vc use multi-energy sources sum m ing cffcct would affcct the result o f absolute cfilcicncy T o avoid this eư o r, single energy gam m a sourccs w ere usually used However, almost o f them have short h alf life and only use in a few months That s why, the multi-energy gam m a sources \\ crc used in this p ap er to calculatc the clTiciency calibration It can be assum ed that in gam m a m easurem ents using m ulti-cncrụy so u rces the counting loss ratios in every peak causcd by the sum m ing cffcct w ere about the sam e [2] 'I’hcn, if we know n relative efficiencies and transformation factor, the absolute efficiencies can be o b la m ed bv follow relation ỉ:(E)^t(E)cXE) w h e r e c ( E ) IS t h e a b s o l u t e dclcclion ^2) e flic ic n c y at e n e rg y o f /: /(/:) IS t h e transform ation factor corresponding to energy o f i.rilĩ) is the relative efficiency value at clicrgy o f E |2| To determine ihc relative efficiency curvc we used two gam m a sources (source 1) and ' (source 2) By chosc ihc photo-peak cfilcicncy at energy Ei (source 1)equal 100%, w c obtained value o f relative efficicncy at energy Eị (source 2) as follow: ( £ )J = c,i.rc'V rt V where Ê, ^2 i ' Ơ- \ « ,(£ ,) À A i'i Í \ Hu the (3) (-£" ) i s the relative efficicncy for energy Ei o f source 1, usually it is taken as 100%, { E ) is the relative cfficicncy for energy Ej o f source 2, o f source at energy E, and source at energy at the m easurem ent time, { E ị ) and i i j { E ^) arc the count rates A| and A arc the activities o f source and source ( z r ,) and { E ị ) are branching ratios o f sourcc and source [2], 1.2 Energy resolution as a function o f energy The energy resolution is a m easure o f the dctcctor’s ability lo distinguish closcly spaced lines in the spectrum The overall energy resolution achieved in a germ anium sy stem is norm ally determined by a com bination o f three factors; the inherent statistical spread in ihe n u m b e r o f charge earners, variations in the charge collection cfficicncy, and contributions o f cicclric noise W hich o f these factors dom inate depends on the energy o f the radiation and the size and inherent quality o f the detector in use The full width at h a lf m axium Wj o f a typical peak in the sp cctru m due to the detection o f a m onoenergetic gam m a ray can be synthesized as follows = W ị^W l+ W Ị (4) W here the w , values on the right-hand side are the peak widths that w o u ld be observed due only to effects o f carricr statistics, charge carriers, and electronic noise crcatcd B V Lout CÍ aỉ / V N i ỉ Jo u rn a l o fS cicn cc M athem atics - Ị% \sics 25 (2009) 231-236 - I h e lirst o f t h e s e ĩ a c t o r s , rcỊMCscnls ih c i n h e r e n t s ta tis t ic a l n u clL iatio n 233 m the n u m b e r o f chargc earn e rs and IS ụivcỉi by: It',; = ( j y F c / ; W here V is ỉ-;ino factor, r is cncruv ncccssary to creatc one clcctron-hole pair, and E is the gammaray energy - T h e conlribulion o f ihc second term, I V y , is due to incom plete chargc collection and is most signiticant in detectors ' t o o p t i m r / c t h e t h i c k n e s s OÍ' t h e ( i c i n a c t i v e l a y e r in o r d e r t o brini* i n t o a c c o r d a n c c t h e experimental and calculated enicicn c ics for vcr>'-lovv energies This work is fmancialy supported by Project Q G -09-06 o f V N l I References [1] Lcnn F, Knoll, "'HiJihdiioii (Icivciion a n d tn c a su rv m e n f' John VVilcy & Sons, S ccond cdilion, (1989) [2] Nguyen Van Do ct al, " Determination of absolute cfficicncy of high punlv Gc dctcctor" Communicalion inPhyics, [3] (2003) 233 J Lin» E.A Henry, and k.A Mcycr, ‘ Dctcciion Efficicncy of Gc(Li) and HPGc Dclcctors for Gamma Rays up to 10 13 M c w r ỈEEE Tnws on Nucl Sci NS-28, No (1981) 154S [4] A,F Sanchcv-Rcycs, ct jL “ Absolute F.rncicncy Calibration Function for the r-Jicri;y i^ani;c 63-3054 kcV for a Coaxial [5] C ategories o f P hoton Di’tcctors, Ortcc Com pany, 2008 [6] 1AÍỈA Co-ordinated Rcscarch Program Gc(Li)Dctcctor AW/ ỉnsír and Sícih «28(1987) 123 191)1 X y a n d ị^am m a-ray sUvỉiỈLỉnỉs f o r (ỉciecíor calibration, lAEA- TECD(X'-619 [7] I Vukanac, M Djurascvic', A Kandic', D Novkovic', L Nadjcrdj, z Milosevic, "Expi'fiftienial deicnntnưỉion o f the ỊỈPGe speciromctcr eJficiencY curve \ Applied Radiation and Isotopes 66 (20()S) 792 ... counting time We calculated relative cfficicncy o f G E M 40P detcctor by chose cfficicncy at energy o f 356.013 is equal 100% and used the formula (3) to calculated relative ciTicicncy o f other... calculatcd by the formula (1) The result o f relative and absolute efficiency can be shown in Table T able Calculation o f relative and absolute efficicncy o f GI-M 40IM E (keV) Br (%) N Relative... widths that w o u ld be observed due only to effects o f carricr statistics, charge carriers, and electronic noise crcatcd B V Lout CÍ aỉ / V N i ỉ Jo u rn a l o fS cicn cc M athem atics - Ị%