NGHIEN CUtJ AP DUNG CHU'OfNG TRINH ko-lAEA TREN LO PHAN ITNG HAT NHAN DA LAT
Cao Dong Vu*, Tr^n Quang Thien, Nguyin Thi Sy, H6 Manh Diing va Nguyen Nhi Diln Vien Nghien cdu hgt nhdn, 01 Nguyen Tie Lire. Dd Lgt. Lam Ddng
*Email: caodongvi^^aboo.com
Abstract: The pneumatic 7-1 and rotary rack (Lazy Susan) facilities are two main irradiation channels for neutron activation analysis at Dalat research reactor. The experiments for characterizing these two irradiation facilities at June, July and August, 2010 by ko-IAEA using Al-0.1% Au, Al-0.1% Lu, 99.98% Ni and 99.8% Zr monitors have been done. The neutron spectrum parameters include: (1) Thermal neutron flux ((|)ih); (2) The ratio between thermal neutron flux and epi-thermal neutron flux (f); (3) The a factor describing the neutron flux distribution I / E ' ' ^ ^ , and (4) The neutron temperature (Tn). This study provides the first database for further studying and applying ko-IAEA at Dalat Research Reactor in the future.
Tir khoa: Phan tich kich hoat natron (NAA), phuong phdp k-zero, chuong trinh kO-lAEA
I. GlQl THIEU
Phuong phap luan k-zero trong phan tich kich hoat notron (Neutron Activation Analysis - NAA) dugc gioi thieu l4n dau tien vao nam 1974 boi hai tac gia la F. De Corte va A. Simonits. Tu do cho den nay, ko-NAA luon duoc quan tam phat trien tai nhieu phong thi nghiem (PTN) NAA va da dugc Hiep hgi phan tich bat riban (Nuclear Analytical Community) cong nhan nhu mgt phuong phap phan tich chuan hoa .
Theo mgt s6 th6ng ke khong chinh thurc cua Co quan Nang lugng quoc te (Intemational Atomic Energy Agency - IAEA), tinh den nam 2007, hon mgt nua so PTN NAA tren the giai dang nghien cuu, phat trien hoac su dung phuong phap ko-NAA ^^l
D8 dap ling nhu cau sir dung ko-NAA tren toan cau, nam 2003, y tuong xay dung mot cong cu phan mem mang tinh dong bg dugc khoi xuong va bao trg boi IAEA. Den nam 2005, phien ban dau tien (ver 1.0) cua chuong trinh ko-IAEA chinh thuc dugc ra doi. ko-IAEA la mgt phan mem than thien voi nguoi sir dung, co tinh linh boat va chuyen nghiep cao, duoc IAEA cap mien phi cho cac quoc gia thanh vien va da nhan dugc su huong ung nhiet tinh tir phia nguoi su dung [1,2].
Phan mem ko-IAEA dugc thiet ke va phat trien boi 2 tac gia chinh do IAEA de nghi la Marcio Bacchi va Menno Blaauw (kO-news-www.kOnaa.org). ko-IAEA co hai dac tnmg moi:
(1) Cach tiep can Holistic dugc su dung trong thuat toan xu ly pho gamma; (2) Viec chuSn hieu suat detector trong chucmg trinh ko-IAEA sir dung giai thuat Monte Carlo [3].
Q Viet Nam, phuong phap chuan hoa ko-NAA da dugc bit dSu nghien cuu tai Vien Nghien cuu hat nhan (NCHN) tu nhirng nam 80 cua the ky truoc. Den nam 2002, chuong trinh ko-Dalat do TS. H6 Manh Diing thiet ke chinh thuc ra doi. Mac du ko-Dalat con mot so ban che nhat dinh nhung den thoi diem tap thS tac gia nghien cihi va tim bieu de ap dung chuong trinh ko-IAEA thi ko-Dalat \h\ la chuong trinh ko-NAA duy nhit dugc ap dung tai Vien NCHN [4].
De trien khai ap dung chuong trinh ko-IAEA tren 16 phan ung (LPU) hat nhan Da Lat, viec truoc tien phai thuc hien la chuan boa he do ph6 gamma va cac kenh chieu xa. Viec hieu
Hgi nghi Khoa hgc vd Cdng nghe hgt nhdn todn qudc Idn thu IX, Ninh Thudn 18-19/8/2011 309
chuan hieu suat cho h§ do ph6 gamma tai PTN INAA ciia Vien NCHN dugc chung toi tiSn hanh bang each su dung hai nguon gamma chuan la Cs-137 va Eu-152, day la cong viec thong thu6ng cua nhimg nguoi lam thuc nghiem ve vat ly hat nhan. Tuy nhien, d l chuin hoa cac kenh chiSu xa tren LPLT bing bg la do ehuyen dung thi cac thi nghiem doi hoi phuc tap hon.
Trong bao cao nay chung toi trinh bay eac thi nghiem va k^t qua tinh toan xac dinh cac thong s6 pho notron tai hai kenh chieu xa khi nen 7-1 va mam quay ciia LPlf hat nhan Da Lat trong cac dgt 16 lam viec vao cac thang 6, 7 va 8 nam 2010 bing eac la do Ai-0,1% Au, Al-0,1%
Lu, 99,98% Ni va 99,8% Zr. Ket qua thu dugc sg dugc luu tru trong co so dir lieu co ban (permanent database) ciia chuong trinh ko-IAEA theo thoi gian va dugc su dung cho qui trinh ko-NAA de thuc bien cac phep phan tich ve sau.
II. THUC NGHIEM
De tien hanh thuc nghiem chuan hoa kenh chieu xa bing chuong trinh ko-IAEA va bp la do chuyen dung, truoc tien phai tien hanh khai bao cae thong tin lien quan den la do duge su dyn^ nhu: ham lugng, sai s6, dang hinh hgc, thanh phin chit nIn (matrix),... Tiip theo phai tien hanh dinh nghia kenh chieu xa bang cac thong s6 khoi tao ban diu nhu thong lugng notron nhiet - ^n, (4xl0'^), he s6 f (9,8; 40), tham s6 a (0,017; 0,073), nhiet do notron Tn (300),... Cac gia tri kh6i tao dugc khuyen nghi boi tac gia cua chuong trinh nhim xae dinh su ton tai cua cac k§nh chieu. Cuoi cimg la khai bao detector sit dung trong qua trinh do pb6 gamma ciia la do.
1. So^n thao co so* du lieu co ban (permanent database) cho chuong trinh
Certificates: La do: Khai bao thanh phan, ham lugng va sai so ciia cac loai la do dugc su dyng trong qui trinh bao gdm: Al-0,1% Au; Al-0,1% Lu; 99,98% Ni; 99,8% Zr va hon hgp tat ca cac la do tren (bon loai la do Au, Lu, Ni va Zr nhap chung thanh mgt mlu, dugc xem nhu mgt la d6 hon hgp). Nguon gamma chuan: Khai bao ten dong vi, boat do, ngay san xuat, v.v... ciia tat ca cac nguon diem don nang, da nang sir dung trong hieu chuan he do.
Detectors: Tai PTN INAA dang sir dung detector HPGe, model: GMX-30190 (ORTEC), CO cac kich thuoc nhu trong Bang 1, cac so lieu nay do nha san xuat cung cap.
Bdng I. Kich thuac cua detector duac sir dung trong bdo cdo ' Detector
Loai
Tinh the
Cua so
Khoang each tir Vimg hoat
Duong kinh (mm) Chieu dai (mm) Lop chet Phia tren (mm)
Phia hong (mm) Duong kinh (mm) Chieu day (mm) Vat lieu
eua so den tinh thi (mm) Duong kinh (mm) Chieu cao (mm)
MAN-GMX (ten) GMX-30190 (model) Dong true 57,0 73,6 0,05
.
67,1 0,5 Beryllium 3,0 11,0 66,9 (*) Sd li?u do nha sdn xuat cung cdp
310 Hdi nghi Khoa hgc vd Cdng nghe hgt nhdn todn qudc idn thu IX. Ninh Thugn I8-19/8/2011 Facilities: Hai kenh chieu xa su dyng cho NAA tren LPU hat nhan Da Lat dugc khao sat trong nghien cuu nay la kenh khi nen 7-1 dimg cho cac phep chilu ngan va trung binh (Tj^: tir 45 giay den 20 phut) va mam quay su dung cho phep chieu dai (Titr>20 phiit). Trong chuong Uinh ko-IAEA, cac thiet bi chieu x^ dugc dac trung h6a theo thoi gian, co nghia la dS dua mgt kenh chilu xa vao su dung, viec truoc tien !a phai mo ta dac tnmg kenh chilu mpt each chinh xac trong co so dQ lieu co ban eua chuong trinh, dong thai de xac nhan su t6n t^ii cua kenh chilu do. Kenh chilu xa sau khi dugc chuan boa, cac thong so lien quan den ph6 notron nhu thong lugng notron nhiet (<}>ih), nhiet do notron (Tn), h? so alpha (a), he so f,.., dugc xac dinh va luu trir trong permanent database.
Tir thoi dilm do, cac kenh chilu da sin sang dl sii dung. Chi tilt vl thi nghiem dac trung hoa cho hai kenh chilu xa tai LPLT hat nhan Da Lat dugc trinh bay trong Muc 3.
2. Chu^n hoa he do ph6 gamma bing chucmg trinh ko-IAEA
Hai ngu6n gamma chuin Cs-137 va Eu-152 dugc sur dung dl chuan hoa he pho k^
gamma tai PTN INAA, Vien NCHN Da Lat. Kit qua duong cong hieu suit va dinh tren t6ng ciia detector GMX-30190 tai vi tri each detector 108,6 mm (H=6) dugc trinh bay tren cac Hinh 1-4.
J M.in-GI)1X at laS,C i i i i i i (lef 10S.6 mill) I
lU w' 111' 10-*
irr*
1 0 '
y'
( '
jcmTirfrlKL A
Hinh 1. Duang cong hieu sudt vd dinh tren tdng tgi vj tri cdch ddu dd 108,6 mm (H=6)
Hgi nghi Khgg hgc vd Cdng nghe hgt nhdn todn qudc Idn Ihi IX, Ninh Thudn 18-19/8/2011 311
fcti^-kO.IAEA"^^'^ Hit EOn !(iKtniinanat)ss View [rradabon (Kilitf DtttOa Q V ] C Tools t*\i
"OIB
(S| + + if '
I'E
iOOOO Z 10
!S3niple2(&i-[53 t W l . IMT RSL
Hinh 2. Dudng khdp cdc diem thuc nghiem cua hieu sudt tgi vi tri H=6
Hinh 3. Ket qud bdng sd ciia hieu sudt tgi vi tri cdch ddu do 108,6mm (H=6), ^=1,1
312 Hdi nghi Khoa hoc vd Cdng nghe hgt nhdn todn qudc idn thir IX. Ninh Thudn 18-19/8/2011
k^' Data Manager / Detectors
f' Calibration enabled
Distance [mm): | ix^LG Faramerei
31 a2 93 a4 3S ae
Value 1
•-O.S076'K3 .6.ie49SB.
-O.9Z60352 es'teac -0.0001143053
-1.470417
DelecloT
JMan-GMX
"3
W Enabled 'I IGMX-INAA Lah Dalat
Efficiency calibiation:
| 0 9 M u g / 2 0 1 0 3
admin allNAA4-VA)0 1 ^ Display information on detector i
Hinh 4. Cdc M sd ciia hdm khop bgc 5 cua hi?u sudt tgi vf tri H=6
3. Thi nghiem mo ta d^c trung thiet bi chieu x^
Cac thong s6 ph6 notron tai hai kenh chieu xa duge xac dinh bang bg la do Au, Lu, Ni va Zr. Cac dilu kien thi nghiem dugc dua ra trong Bang 2.
Bdng 2. Cdc dieu ki?n chieu xg bg Id dd Au. Lu. Ni vd Zr - Thoi gian chieu /
Vj tri chieu + Loai Id do (khoi luong, mg)
-15phufkenh7-l - 1 gio/mam quay + Al-0,l%Au(~4) + Al-0,l%Lu(~4) + 99,98%Ni (-30) + 99,8%Zr(~I0)
Thoi gian ra
4-6 gia
~1 ngay
~3 ngay
Thoi gian do
-1200s doi voi la do Ni va Lu -1800s doi voi la do hon hgp (combination)
- 7200s doi v6i la do Zr va la do hon hop
- 900s doi voi la do Au - 7200s doi v6i la do Zr - 10800s d6i voi la do Ni va Lu -18000s ddi vol la do h5n hop
Bong vi [Tm, ET(keV)]
"Ni [2,5h, 366,3, 1115,5,1481,8],
"""Lu [3,6h, 88,4]
"Zr [16,7h, 743,4]
"Nb[16,7h, 657,9]
'"'Au[2,7d, 411,8];
'"Lu[6,7d, 112,9, 208.4]; ''Zr [64d, 756.7]; "Nb [64d, 765.8]; "Co [70,8d, 810,8]
Hgi nghj Khoa hgc vd Cdng ngh? hgt nhdn todn qudc idn thu IX, Ninh Thudn 18-19/8/2011 313
III. KET QUA VA BINH LUAN
Ket qua tinh toan cac thong so pho notron tai hai kenh chilu mau dung cho phan tich kich boat notron tai L6 phan iing hat nhSn Da Lat bang chuong trinh ko-IAEA va chuong trinh ko-Dalat cua cac dgt 16 1dm viec trong cdc thang 6, 7 va thang 8 nam 2010 dugc trmh bay trong Bang 3.
Bang 3. Ket qud tinh todn cdc thdng sd phd natron tgi hai kenh chiiu 7-1 vd mdm quay
Thang
6/2010
7/2010
8/2010
Trung binh
Gid tri cu
Kenh chieu
7-1 Mam quay 7-1 Mam quay 7-1 Mam quay 7-7 Mam quay 7-1 Mdm quay
*«-IAEA Thermal
(n/cm'/s) 5,448E+12 3,581E+12 5,218E+12 3,993E+12 4,936E+12 4,037E+12 5,20E+12 3,87E-H2
_ -
T (K) 311 299
- -
314 295 313 297
_ -
Alpha
-0,036 -0,018 -0,034 -0,016 -0,044 0,003 -0,038 -0,010
_ -
/
12,0 53,8 11,8 52,9 12,5 51,2 12.1 52,6
_ -
Ao-Dalat Thermal Alpha
(n/cm'/s) 4,814E+12 3,643E+12 0,018 5,463E+12 0,010 3,915E+12 0,088 4,847E+12 4,052E+12 0,035 S,04E+12 0,010 3,87E+12 0,047 S,10E+12 0,017 3,70E+12 0,073
f
_
52,4 9,7 34,1
_
43,4 9.7 43,3 9,8 40,0
Epi/Fast
0,192 0,423 0,173 0,538 0,189 0,442 0,185 0,468 0,143
'
Doi voi thong lugng notron nhiet eiia 3 dot thuc nghiem tai 2 kenh chieu mau 7-1 va mam quay giiJa hai chuong trinh la kha phu hgp, do lech tuong doi giiia cac ket qua tuong ung la xap xi 10%. Doi voi tham so nhiet dg notron chi co gia tri ciia chuong trinh ko-IAEA, ko-Dalat khong tinh thong so nay. Gia tri trung binh nhiet do notron cua kenh 7-1 tinh trong cac dgt thang 6, 7 va 8/2010 (n=3) la 313''K-39,85'*C va gia tri nay ciia mam quay la 297°K ~ 23,85°C. Ket qua tinh he so alpha co su sai khac giiJa chuong trinh ko-IAEA va ko-Dalat, chuong trinh ko-Dalat luon cho cac gia tri alpha > 0 va ngugc lai doi voi ko-IAEA luon cho ra cac gia tri alpha <0. Mac du trgng so dong gop cua gia tri alpha trong ket qua cuoi ciing cua phep phan tich la khdng Ion, tuy nhien, trong tuong lai gan chung toi se co nh&ng thi nghiem tiep theo nham tim ra 161 giai thich ciia su sai khac nay. Doi voi he so f, chuong trinh ko- IAEA luon cho ket qua Ion bon ko-Dalat, tuy vay, phin Ion ket qua cua 2 chuong trinh la kha phii hgp va deu co the sijr dung dugc, khong co sai khac nao 1cm. Cac ket qua nay se dugc lim trQ- trong co so dii lieu co ban cua chuong trinh ko-IAEA va sii dung trong qui trinh ko-NAA cho cac phep phan tich ve sau.
314 Hdi nghi Khoa hgc vd Cdng ngh? hgt nhdn todn qudc Idn thu IX. Ninh Thudn 18-19/8/2011
IV. KET LUAN
Lin ddu tien chuong trinh ko-IAEA dugc ap dung thanh c6ng tai hai kenh chilu xg khf nen 7-1 va mam quay cua LPU" hat nhan Da Lgt. Ket qua nay \k tiln dl cho viec triln khai ap dung qui trinh phan tich ko-NAA bang chuong trinh ko-IAEA tai PTN INAA ciia Trung tam Phan tich, Vien Nghien cuu hat nhan.
Trong thoi gian toi chiing toi se ti§p tuc tim hieu va khai thac cac chiic nang khac ciia chuong trinh ko-IAEA nhu: Kiem soat va dam bao chat lugng (Quality Assurance and Quality Control - QA/QC) cho qui trinh phan tich, phuong phap kzero trong phan tich kich boat gamma tiic thoi (Prompt Gamma Neutron Activation Analysis - PGNAA),... Dong thoi se trien khai ap dung chuong trinh ko-IAEA trong vi8c phan tich cae mau tb\rc te.
TAI LIEU THAM KHAO
[1] M. Rossbach, M. Blaauw, "Progress in the ko-IAEA program", Nucl. Instr. and Meth., A 564, pp. 698-701,2006.
[2] M. Rossbach, M. Blaauw, M.A. Bacchi, Xilei Lin, "The ko-IAEA program", J. Radioanal.
Nucl. Chem., Vol. 274, No. 3, pp. 657-662, 2007.
[3] M. Blaauw, "The holistic analysis of gamma-ray spectra in instrumental neutron activation analysis", Nucl. Instr. and Meth., A 353, pp. 269-271, 1994.
[4] Ho Manh Dung, "Nghien eiiu phat trien phuong phap^ k-zero trong phan tich kich ho?t notron 16 phan iing hat nhan cho xac dinh da nguyen to", Luan an tien si Vat ly, Dgi hpc KHTN, Dai hgc Qu6c gia Tp.HCM, 2002.