TAP CHl KHOA HOC - DAI HOC DONG NAI, SO 02 - 2016 ISSN 2354-1482
XAC LAP THAM SO THCH GIAN CUA HE PHO KE TRUNG PHUNG CHO PHAN TICH KICH HOAT
ThS. Trwang Van Minh' PGS. TS. Phgm Dinh Kkang^
TS. Nguyin Xudn Hdi' ThS. Le Thi Thanh Hd^
ThS. Phan Vdn Chudn^
TOM TAT
Ung dung phucmg phdp trting phiing trong phdn tich fdch hogt da vd dang dugc triin khai a mpt so nu&c trin thi giai. Tie ndm 2005, tgi Vien nghien cuu hgt nhdn (NCHN), he pho ke trung phung gamma - gamma dd duac thiet lap cho viee thu nhan sd lieu hgt nhdn. Gdn ddy, he ndy cdn duac trien khat ieng dung trong phdn tich kich hogt natron. Npi dung bdi bdo ndy trinh bdy mpt sd kit qua xdc lap cdc tham sd th&i gian cua hi phd ke trung phitng su dung trong phdn tich kich hogt a vung ndng luang thdp; kit qud xdc lap cdc tham sd m&i eho kenh th&i gian da dp dgng thu nghiem phdn tich mdu dia ehdt.
Tir khda: Hi phd ki triing phung; phdn I. M d d a u
He phd kg trung phiing gamma - gamma ghi "sy kien-sy kien" da dugc thiet lap tgi NCHN. Cdc nghien ciiu tmdc ddy trgn he ndy chii yeu tap trung d cau tnic hgt nhan, ma phdn chinh Id cdc raiic phan ra ndi tang [1,2]. Thdng tin tii phd thdi gian (phd TAC) ciia he dimg de giam phdng, chgn cdc sy kien tning phiing thyc. Tuy nhign, tmdc ddy do do phdn gidi thdi gian ciia he chua tdt (khodng 14ns) [2], nen khd ndng cung edp thdng tin tir phd thdi gian eiia he chua dugc nhigu. De nang eao kha ndng eung cdp thdng tin thuc nghiera eua he phd ke trimg phung gamraa - gamma ghi "sy kien-sy kien" vd khd ndng gidm phdng frong phep do, nhdm nghign cim da cai thien do phdn giai tiidi gian cua he, xdy dung thudt toan gate sd lieu eua phuong phdp. Kit qua xdc lap tdi uu cac tham sd thdi gian eiia he ed y ngbia ldn ttong viec dp dung he frong pban tich kich boat.
'Tnrong Dai hoc Dong Nai
^Vien Nghien ciiru Hal nhan Da Lat
^Tnrong Cao dang Cong thuong Tp Ho Chi Minh i
*Tnr6ng D^ hgc Da Lat
tich kich hogt; tham sd thai gian Trong nghien cim nay, nhdm tac gid da thiet lap dugc bd tham sd tdi uu eua he va dp dung de pban tich radu dja chat bang phuang phdp tning phimg garama garama.
2. PhiTtfng phap thuc nghiem 2.1. Cdi thien dp phdn gidi th&i gian
He phd kg triing phimg gamma - gamma ghi "sy kign-sy kien" tgi Vien NCHN dugc md ta fren hinb 1. HPGe 1 vd HPGe 11 la hai detector ban dan kieu GMX 35. Cac khdi dien tu va thara sd duge md ta chi tiet frong tdi lieu tham khao [1, 2, 3]. Do phdn gidi thdi gian eua he ngoai viec phu thude vdo chat lugng cdc detector, chat lugng cac khdi dien tu, cdeh bo tri thi nghiera, thi van de quan frgng la do phdn gidi thdi gian cua he phy thudc rdt nhieu vao viec lua ehgn cdc tham so cua kgnh thdi gian ciia he. Tuy nhien, raudn chgn lya cdc tham sd tdi uu
TAP CHi KHOA HOC - DAI HOC DONG NAI, SO 02-2016 ISSN 2354-1482 cho kenh tiidi gian, tbi ngudi lara thyc
nghiem can phdi hieu chinh sao eho vdn dara bdo ba dilu kien sau:
Hieu suat ghi cua todn hg phd kg khdng bi dnh hudng nhieu;
Dinh phd ludn cho do rdng eye dai tdt nhat cd thg, va ti sd dien tich dinh fren phong Id cue dai;
Phd nang lugng gitra cdc kenh can ed sy ddi xiing nhau.
Hinh 1. Cdu hinh hi do trung phung gamma - gamma "su kien-su kien ".
De giara thdi gian khdo sdt, dao ddng ky dugc sii dung de ehgn nhanh td hgp ede gid tri cho khugch dai lgc lua thdi gian (TFA) theo tieu ehi tin hieu cd bien do ldn vd tuyen tinh. Viec dat nguong cho khdi phdn biet ngudng hang dugc thyc hien d gid tri ngudng dudi la 121 keV. Ci gid tri dugc ehgn, ngudng dugc ddt khdng qud thap nham giam anh hudng ciia nhilu, ddng thdi vira du eao de khdng cdt mat tin hieu. Sau khi da udc lugng duge gia tri ngudng, cac phep do khdo sat dugc thyc hien quanh cdc gid fri ndy d l chgn ra gid tdt nhdt.
Dg thu nghiem chdt lugng cua cdc thara sd dugc chgn, edc phep do vdi Co- 60 da dugc thuc hi?n. Dai thai gian cua TAC dugc dat la 100 ns vd ADC diing cho phan tich phd TAC dat d Ik.
2.2. Kiem tra ki do sau kki hieu chink tham so
Diing radu chudn Id raau dia chat [4], dyng trong tiii nylon sach va han kin vdi kich thudc tiii dung radu Id lOmra x 10 mm, khdi lugng mdu la 148,3 mg vd chieu tai radra quay cua Id phdn iing hat nhan Dd Lgt, thdng lugng nation tai vi tri chilu mdu ~ 3,76.I0'Vcm^s [5]. Mau dugc dgt trong container nhdm va ehieu frong thdi gian 10 gid.
Sau khi ket thuc chilu, mdu dugc d l ra vdi thdi gian Id 90 ngay. Sau dd, tiln hanh do vdi thdi gian 100 gid d chl do do triing phimg.
Thudt todn xii li sd lieu trong chg do do triing phiing gamma - garama gbi
"su kien - sy kien" dugc trinh bdy theo hinh ve sau:
TAP CHi KHOA HOC - DAI HOC DONG NAI, SO 02 - 2016 ISSN 2354-1482
Hinh 2. So dd thudt toan xir H sd lieu.
Gidi ban do va ham lugng nguyen td trong mdu dia chdt cua phuong phdp do trung phung gamma duge tinh theo edng tiuic (1) va (2) sau ddy:
3.29C
13(7
Trong dd:
CDL^ gidi hgn do tinh theo don vi hdm lugng (ppm);
C: hara lugng ciia ddng vi quan tdm ttong mau phdn tich (ppm);
P: dien tich dinh phd (sd dem);
B: dien tich nen phdng dudi dinb (sd dem);
t: thdi gian do raau (giay);
npvar\B Id hang sd.
Ham lugng nguyen td frong mau dugc tinh bang phuang phdp tuong ddi:
[IV.D.C
0)
W.D.C
(2)
TAP CHi KHQA HOC - DAI HOC DONG NAI, SO 02 - 2016 ISSN 2354-1482 Trong dd:
p Id bam lugng ciia nguyen td can phdn tich (g/^\
W la khdi lugng mdu phdn tich (g);
w la khdi lugng nguygn td quan tam trong mdu chudn bang bam lugng nhan vdi khdi lugng radu chudn (g);
Np la sd dgra cua dinh nang lugng tia gamma;
S = 1 - exp(-/l t,) Id be sd bao hda, ti Id thdi gian chigu;
D = exp(- X td) la he sd hieu cbinh thdi gian ra, tj la thdi gian phdn ra;
C = [1 - exp(-ltc)]/(-itc) Id he sd hieu chinh thdi gian ra ttong khi do, tc la Ihdi gian do;
Ki hieu "a" chi mau phan tich, vd "s" chi mdu chuan.
3. Ket qua
3.1. Pko tk&igian cua ke
Equation
Adj R-Squ
A A A A A A A
y=yO * (A/(w w)-2) a 0,99335
yO x c w A Sigma FWHM Height
sqrtfPI/2)))-e
Value 9.75005 185.12175 82,3057 78742,258 41,15285 96,90756 763,33999
Kp(-2*((x-XOf/
Standard En 1.16515 0,1781 0,39304 390,00034
Phd dugc do vdi ngudn Co-60 hogt do 0,95 ^Ci; thdi gian do I gid. Kgt qua kilm nghiem be do trung phung "sy kien - su kien" tai Vien NCHN tbeo kenh thdi gian cd he so 0,098 ns/kenh. Thye nghiem cho thdy dg phdn gidi thdi thu dugc tir qua trinh Idra khdp Id FWHM=
96,9 X 0,098 = 9,46 ns.
Hinh 3. Phd thdi gian do vdi Co-60.
3.2. Kiim tra, phdn.tich mdu Phdn tieh mdu bang phuang phap chuan don de danh gia kha nang dap ung Clia phuang phap frong pban tich kieh hogt. Kit qua bieu dien radi quan he giiia toe do dgm va khdi lugng-mau dugc trinh bdy d biilh 4.
TAP CHl KHOA HOC - BAI HOC BONG NAI, SO 02 - 2016 ISSN2354-1482_
r. c
lclidiLiraiigiDSu(Mg)
y=i,9ix-ei,4
•' R'=0,9974
loi lif^ng m^u {pg)
Hinh 4. Su phy thudc giiia tdc do dgra vd khdi lugng mdu bang phuang phap do triing phiing
Tien hanh phan tich nguyen td Selen ttong mdu dia chat bdng phuang phap triing phimg, phuang phap xii li sd lieu duge trinh bay d rauc II.2. Phd do dan vd do triing phimg cua radu dia chat dugc trinh bay d Hinh 5.
35000 - 30000 - 25000 - 20000 - 15000- 10O0O - 5000-
-5000 - -10000 - -15000 - -20000 - -25000 - -30000 -
_JM^
1
sL
1
I
-...JL_1J__
s 5
^
1
J4iLi^
t
•?
- 1
B
,..
' .
Do ddn
J _ J L L _ ^
o u t n g phiing
'
•I't., u..
250 500 750 1000 1250 1500 Nang li/dng (keV)
Hinh 5. Phd do don vd do ttTing phiing raau dai chdt
T A P C H i KHOA HOC - DAI HOC DONG NAI, SO 02 - 2016 ISSN 2354-1482 Trong mdu dia chdt, cd 46 nguyen td cd
mat ttong mdu [4]. Tuy nhien, kit qua d Hinh 5 cho thdy frong phep do tning phiing da logi bd dugc cac ddng vi nhieu Bang 1. Hdra lugng Se trong mdu phan tich
vd giam nen phdng dang ke. Ket qua xac dinh hdm lugng Se frong mdu dia chdt dugc ttinh bay frong Bang 1.
Nguyen to
Se
Gia tri xac dinh (ppm)
1,86 ±0,13
Gia tri chiing nhan (ppm)
2
Z-Score
1,08 Kit qua phdn tich ham lugng Se
frong mdu fren Bdng 1 cd Z-Score < 2, dieu ndy cho tiidy gid tii nay phu hgp vdi gia tri chimg nhdn ciia mdu chuan.
4. Kit luan
Kit qud khao sdt tham sd he do cho thdy phd thdi gian thu dugc cd do phan gidi Id 9,46ns, nhu vdy su thay cdc dau do vd tdi uu cac tham sd da cdi thien do phan gidi thgm 4 ns so vdi cac cdng bd trudc day.
He phd kg triing phiing Gamma- gararaa ghi "sy kien - sy kien" sau khi xac lap mdi cac tham sd kgnh thdi gian da cho do phdn gidi thdi gian rat tdt.
Thuat todn vd chuang trinh xir li pho frong do trimg phung cho phep tach dugc edc dinh chap ciia cdc ddng vi nhilu dnh hudng len viec phdn tich hdm lugng Se frong m l u dia chat.
Nghien ciiu ndy da gdp phdn hoan thien khd nang cua he phd ke triing phimg frong phan tieh kich boat tgi Vien nghien ciiu hat nhdn Dd Lat.
TAI LIEU THAM KHAO
1. Nguygn Xudn Hdi (2010), Ung dung phuang phdp epng bien dp cdc xung trung phitng nghien cieu phdn rd gamma ndi tdng cita Yb vd Sm tren Lo phdn irng Hgt nhdn Dd Lgt, Lugn dn Tien sT, Vien Nang lugng nguyen tir Viet Nam.
2. Pham Dmh Khang, V.H. Tan, N.X. Hai, N.N. Dien (2011), Gamma-gamma coincidence spectrometer setup for neuPon activation analysis and nuclear structure studies, Nucl. Instr. and Meth. A631.
3. Vuong Huu Tdn va cdc edng sy (2006), Nghiin cieu cuang dp chuyin d&i gamma noi tdng vd sa do miec kich thieh vung ndng luang trung gian cua cdc hgt nhdn Sm, Ta, Ni vd ^^^U", Bdo cao d l tdi nghien cim cdp bg nara 2005-2006, Dd Lat.
4. NIST (2013), Standard Reference Material Montana II Soil- 271 IA.
5. Cao Dong Vu (2014), Characterization of neutron spectrum parameters at irradiation channels for neutron activation analysis after full conversion ofthe Dalat nuclear research reactor to low enriched uranium fuel. Nuclear Science and Technology, 4(1): p. 70-75.
TAP CHI KHOA HOC - DAI HOC DONG NAI, SO 02 - 2016 ISSN 2354-1482_
DETERMINATION OF TIMING PARAMETERS OF THE COINCEDENCE SPECTROMETER FOR NEUTRON ACTIVATION ANALYSIS
ABSTRACT
The application ofthe coincidence method ofthe neutron activation analysis has been put into operation in some countries in the world. Since 2005, at Dalat nuclear research institute, the gamma-gamma coincidence spectrometer has been used to collect data of nuclear. Recently, this spectrometer has been also widely used in neutron activation analysis. This paper shows some results ofthe established gamma — gamma coincidence system parameters used in neutron activation at low energy range; and applied testing of soil sample.
Keywords: The coincidence spectrometer; neutron activation analysis; timing parameter
