Tap chi KHOA HQC DHSP TPHCM So 33 ndm 2012
NGHIEN CUtJ DUdNG CONG HIEU SUAT DINH
NANG LUQIVG TOAN
P H A N SLTDUNG CmTONG TRINH DETEFF
T R A N T H I ^ N THANH", C H A U V A N TAG'*, TRU'ONG THI H Q N G LOAN**', MAI V A N NHON"**
T6M TAT
Trong cdng trinh ndy, chuang trinh DETEFF dugc dung de xdc dinh hi?u sudt dinh
y ^ I *i7 * *
ndng lugng lodn phdn cua ngudn Eu tgi vj tri cdch ddu dd 15,3cm (de bd qua hieu chinh trimg phiing tdng ciia cdc lia gamma). Ket qud cho thdy cd su phii hgp tdt giiea hi^u sudt dinh ndng lugng todn phdn thuc nghidm vd md phdng v&i sai bi^t du&i 4% cho cdc dinh ndng lugng chii yeu cua '^'Eu. Dieu dd cho thdy chuang trinh md phdng md chung tdi xdy dung dugc tren chuang trinh DETEFF la ddng tin cdy cho vifc nghien ciru tiip tuc tren h^
phd ke gamma ndy bdng phuang phdp md phdng.
Tir khda: Monte Cario, DETEFF, gamma.
ABSTRACT
Investigating full energy peak efficiency curve by using DETEFF code
In this paper, DETEFF code is used to determine the efficiency of the full energy peak of Eu source at position 15.3cm from the end cap of the detector (to neglect the
sum of coincidence correction of gamma rays). The results show an good agreement between the measured values and simulated one of FEPE with difference less than 4% for main gamma energies of'^Eu. It shows that our simulation program based on DETEFF code is reliable enough for later studies on our HPGe spectrometer by using Monte Carlo Method
Keywords: Monte Carlo, DETEFF, gamma.
L Gidi thifu:
He phd kl gamma Id thilt bj dimg trong phep do vd phdn tich phd gamma de khao sdt ddc trung ciia cdc dong vj phdng xa cd trong cdc mau mdi tmdng dya tren viec xdc dinh ndng lugng cua cdc tia gamma ndy nhdm nhdn di?n vd xdc dinh boat do cua chung. Khi sir dyng
ThS, Tru'dng Ogi hpc Khoa hpc Ty nhi6n, DHQG TPHCM
PGS TS, Tru'dng Dgi hpc Khpa hpc Ty nhifin, DHQG TPHCM
TS, Tryb-ng Dgi hpc Khpa hpc Ty nhi§n, DHQG TPHCM
PGS TS, Trudng Dgi hpc Khpa hpc Ty nhi6n, DHQG TPHCM
he phd ke gamma cd hai yeu td cdn dugc quan tdm la hi^u suat ciia dau dd vd dp nhay ciia h? phd kl.Vdn dl dg nhay cua h? phd ke d^ dugc tdi uu bdd cdc ddc tnmg cua budng chi vd cdc ylu to khac trong qud trinh thilt ke. Vdn dk cdn lai la vi?c xdc dinh hieu sudt cua dau dd t?i thdi dilm do mdu. Vi vdy, xdc dinh lai hi?u sudt tai thdi dilm do Id viec rdt cdn thilt.
Phucmg phdp thuc nghiem dugc sit dyng h-ong qud trinh xdc dinh hieu sudt dinh ndng lugng todn phdn theo ndng lugng Id diing mgt sd ngudn phdt gamma dan ndng da bidt truac boat dg. Tuy nhien cdc nguon nay thucmg cd chu ki
Tap chi KHOA HQC DHSP TPHCM Trdn Thi^n Thanh vd tgk
ban ra ngdn nen sau mgt thdi gian sir dyng cdn dugc trang bi lai. Mdt each khdc la su dyng nhiing dong vi cd chu ki ban ra ddi nhu '"Eu, ^'^Ra dl tinh todn hieu sudt ndy, khi dy dnh hudng ciia hien
f y t f
tugng gamma ndi tdng gay ra sy mat sd dem tai dinh ndng lugng loan phan khi tiln hdnh thi nghiem d khodng cdch gan ddu dd (hieu img triing phiing tdng) can dugc hieu chinh. Ben canh dd, cdc ngudn nay khdng du cdc dinh nang lugng cho loan bd viing quan tdm tir 50keV den 2000keV.
Nhimg khd khdn tren cd the dugc gidi quylt bdng phuang phdp md phdng, vi phuang phdp ndy the hien nhimg uu dilm nhu: khi da kiem tra do chinh xdc ciia cdc thdng sd ban ddu dugc cung cap bdi nhd sdn xuat bdng each so sdnh ket qud cua phuang phdp md phdng vdi ket qud do dugc tir thyc nghiem, nlu ket qud so sdnh cho do sai biet nhd, ngudi ta cd thi dimg phuang phdp md phdng de tinh loan cdc gid tri ciia dii lieu cho viec ldm khdp dudng cong hieu sudt md thuc nghiem khdng cd dugc. Cdc gid tri nay rat hiiu dyng vi nd se cung cdp them sd lieu thyc nghiem cho qud trinh ldm khap va ldm cho dudng cong hieu sudt theo ndng lugng trd nen hodn chinh horn vdi viing ndng lugng tir 50keV din 2000keV.
2. Xac djnh hifu suat bdng thirc nghiem
Ddu dd HPGe dugc dung dl xdc ' dinh gid tri hieu sudt theo ndng lugng cho
> hinh hgc gid dilm '"Eu tai khodng each ' 15,3cm tir ngudn tdi ddu dd dk bd qua ' anh hudng cua sy triing phiing tdng. Cdc ' thi nghiem dugc do tren he phd kl
gamma sir dung dau dd HPGe - GC2018 loai p ciia hang Canberra cd hieu sudt tuong ddi 22,4% vdi dinh nang lugng 1332,5keV tai Bd mdn Vdt li hat nhdn, Trudng Dai hgc Khoa hgc Ty nhien TPHCM. Phd gamma dugc ghi nhan vd xir li tren phan mem Genie-2K [5], hi?u sual thyc nghiem dugc xdc dinh bang cdng thirc sau:
N''(E)
e^(E) = (1)
A.l^(E).l
Vdi e''(E)Ia hieu sudt dinh nang lugng loan phan tuong img vdi nang lugng E, N''(E)ld dien tich dinh ndng lugng todn phdn, A la boat do ciia ddng vi phdng xa, 1^(E) Id xdc sudt phdt gamma, t Id thdi gian do (s).
3. Xac djnh hifu suat bdng mo phdng
Phuang phdp Monte Carlo dugc sir dung khd phd bien de md phdng cdc thiet bi, he do, ddc biet la cdc qua trinh vdt li hat nhdn. Trong cdng trinh ndy, chuang trinh DETEFF [1] dugc dugc su dyng dl tinh hieu sudt dinh ndng lugng todn phdn ciia ddu dd. Bdng viec cung cdp day dii vd chinh xac cdc dii lieu ve thdng sd ki thudt ciia dau dd dugc cung cap bdi nhd sdn xudt dugc trinh bdy trong bdng 1.
Nguon chudn gid dilm '"Eu cd dudmg kinh 3mm, chilu cao 0,76mm cd dudmg kinh ngodi 25,4mm, chilu cao 3,18mm.
Cdc thdng sd khdc cua ngudn nhu chu ki bdn ra, ndng lugng, xdc suit phdt gamma dugc ldy tir co sd dii lieu [6].
Chuong trinh DETEFF se cho ra gid tri hieu sudt theo cdng thirc (2) vd sai
Tap chi KHOA HQC DHSP TPHCM So 33 nam 2012
phdng dudi 0,5% so hat phdt ra tir nguon dugc md phdng la 10^ ljch sir hat. Hi?u suat dinh md phdng dugc xdc djnh bdng cdng thiic sau:
n . X N ' ' ( E )
N nguon (2)
Trong dd e''(E), W {E) , N"«"™
Ian lugt Id hi?u suat dinh ndng lugng toan phan tucmg img vdi ndng lugng E, s6 dim dinh vd sd hat phdt ra tir ngudn.
(2)
Bdng 1. Thdng sd ki thudt cua dau dd HPGe-GC20I8 dugc cung cdp b&i nhd sdn xudt
Mo ta
Dudng kinh tinh the Germanium Chilu cao tinh the Germanium Dudng kinh hdc
Chieu cao hdc
Khoang cdch tir ciia sd den tinh the Be ddy ciia sd
Dudng kinh ngodi cua ddu dd Ldp tiep xiic ben ngodi
Ldp tiep xiic ben trong Ldp bdo ve ben ngodi
Kfch thirdrc (mm) 52
49,5 7 35 5 1,5 76,2 0,86 0,0003
1,5
Vat chat
•
Germanium Germanium
Nhdm Li Bo Nhdm
f y
Bang 2. Gid tri hieu sudt dinh ndng lucmg todn phdn giira md phdng vd thuc nghiem tgi khodng cdch 15,3cm tit be mat dau dd
Ndng lugng (keV) 121,78 244,70 344,28 367,80 411,12 443,97 688,67 778,90
Hi?u sudt dinh ndng lugng todn phdn Thyc
nghiem 0,00406(29) 0,00293(21) 0,00211(15) 0,00202(15) 0,00178(15) 0,00164(13) 0,00114(12) 0,00100(8)
Ldm khdp thyc nghi?m
0,00407 0,00293 0,00213 0,00200 0,00179 0,00167 0,00112 0,00101
DETEFF 0,00423 0,00301 0,00219 0,00205 0,00184 0,00171 0,00115 0,00104
Dg sai bift giOra Ldm khdrp
thvrc nghifm vd DETEFF (%)
3,9 2,6 2,7 2,5 2,5 2.,6 2,7 3,0
Tgp chi KHOA HQC DHSP TPHCM Trhn Thien Thanh vd tgk
867,38 964,08 1085,84 1089,74 1112,08 1212,95 1299,14 1408,01
0,00091(7) 0,00083(7) 0,00076(6) 0,00077(6) 0,00076(5) 0,00069(5) 0,00065(5) 0,00061(4)
0,00092 0,00085 0,00077 0,00077 0,00075 0,00070 0,00066 0,00061
0,00095 0,00087 0,00078 0,00078 0,00077 0,00072 0,00068 0,00063
2,8 2,6 1,5 1,8 2,2 2,9 3,2 2,9 Gid tri 0,00061(4) cd nghia la
(0,00061±0,00004).
Chiing tdi nhdn thay, cdc gid trj nhan dugc khi ndi suy trong viing ndng lugng thyc nghiem Id 121,78keV den
1408,01keV Id khd phii hgp. Tuy nhien, vimg ndng lugng tren 1408,0 IkeV va dudi 121,78keV dudmg cong hieu sudt bi gdy dot ngdt, lam cho viec ngoai suy gid
tri trong viing ndng lugng ndy dan den sai sd ldn nhu hifu sudt ciia 59,54keV (^**'Am), 88,04keV ('°^Cd) vd
1836,05keV (*^Y), do sai biet giira gid tri ndi suy tir ham lam khdp vdi sd lieu md phdng cd do sai biet ldn lugt Id 37%, 14% vd 10%. Hien tugng nay Id do gia trj thyc nghiem khdng dii de khdp hdm cho viing ndng lugng ndy.
0.01
s
1E-3
3E-4
• Thuc nghiim
• Ma phong
Uan khdp thifc nghiCm
30 100 NanBliinns(keV) tooo 2000
Hinh 1. So sdnh hieu sudt giira md phdng vd thuc nghiem tgi khodng cdch 15,3cm tie ngudn t&i ddu dd
Chuang trinh md phdng cd uu dilm lugng 59,54keV (^'^'Am), 88,04keV Id sau khi kilm tra do tin cdy ciia chuang ('"'Cd) vd 1836,05keV (**Y), kit qud trinh chung ta cd thi tilp tyc md phdng trong hinh 2 bilu diln dudng cong hifu cdc dinh nang lugng md trong thuc sudt theo ndng lugng tinh dugc tir md nghifm cdn thilu. Trong cdng trinh ndy, phdng kit hgp thuc nghifm so vdi dudng chung tdi md phdng them cdc dinh ndng thuc nghifm.
Tap chi KHOA HQC DHSP TPHCM Sd 33 ndm 2012
0.01
• • « !
a (/:
a
1E-3
3E4
Thiif nghiOm
Thiic nphiCni kci hap nut phong
Lam khi'rp ihirc nj^hicm kei hcrp mo phoriji
• Lam khtVp ihirc nghiem 30
-I—r—T—!—[
100 Nang Imping (kcV)
' ' ' I —
1000 2000
Hinh 2. So sdnh hi?u sudt md phdng kit hgp thuc nghidm
vd hieu sudt thuc nghidm tgi khodng cdch 15,3cm tir ngudn t&i ddu dd Kit qud cho thdy khi gia tri thyc
nghifm nhdn them gid tri md phdng thi dang hdm liic nay da trd nen lien tyc vd khdng cdn bi gay khiic tai hai vimg ndng lugng dudi 121,78keV vd tren
1408,0 IkeV vd do sai biet trong viing ndng lugng quan tdm tir 50keV - 2000keV cd gid tri cyc dai Id 3%.
4. Ket luan
Trong cdng trinh ndy, chuong trinh DETEFF dugc diing de tinh todn gid tri hieu sudt dinh ciia ngudn Eu vdi 16 dinh ndng lugng quan tdm cho ket qud sai
sd ldm nhdt Id 4%, cho thay chuang trinh md hinh hda he phd ke gamma dimg ddu dd HPGe vd ngudn chudn '"Eu dugc xdy dyng Id ddng tin cdy. Nhiing dp dung lien quan din ddu dd HPGe ndy vdri hinh hoc khdc cd the dugc trien khai dua tren co sd ndy. Nhu vdy phuang phdp Monte Carlo vdi chuang trinh DETEFF cd the hd trg ngudri lam thyc nghifm xdy dung dudmg cong hifu sudt theo ndng lugng mdt cdch ddy du ban trong dieu kifn ngudn chudn khdng nhieu ciing nhu voi cdc cdu hinh ngudn khdc nhau.
Ghi chd: Nhdm tdc gid chdn thdnh cdm an TS Nguyen Vdn Hung da cho chiing tdi dugc sit dung cdc ngudn chudn. TS Nestor Comejo Diaz & Trung tdm an todn bite xg, Cuba vd TS Miguel Jurado Vargas d khoa Vdt li, Spain dd cung cdp cho chung tdi chuang trinh DETEFF
Tgp chi KHOA HQC DHSP TPHCM Trhn Thien Thanh vd tgk
TAI L!$U THAM KHAO
1. N,Comejo Diaz, M, Jurad Vargas, (2008) "DETEFF: An improved Monte Carlo computer program for evaluating the efficiency in coaxial gamma-ray detectors".
Nuclear Instruments and Methods in Physics Research A 586, pp. 204-210.
2. D. Amold and O. Sima (2006), "Calculation of coincidence summing corrections for X-ray peaks and for sum peaks with X-ray contributions". Applied Radiation and Isotopes, pp. 1297-1302.
3. Tmong Thi Hong Loan, Tran Thien Thanh, Dang Nguyen Phuong, Tran Ai Khanh and Mai Van Nhon (2007), "Monte - Cario simulation of HPGe detector response fiinetion with using MCNP code". Communication in Physics, vol I, no I. pp. 59-64.
4. M. Jurado Vargas, N. Comejo Diaz and D. Perez Sanchez (2003), "Efficiency transfer in the calibration of a coaxial p-type HpGe detector using the Monte Carlo method". Applied Radiation and Isotope, pp. 707-712.
5. Genie 2000 Tutorials Manual. (2004), Canberra Industries, Inc.
6. www.laraweb.free.fr
(Ngdy Tda so^n nh$n dugc bdi: 23-8-2011; ngdy chSp nhdn ddng: 26-9-2011)