Top chi Khoa hpc Tnrang Dpi hpc Cdn Tha Pban A • Khoa hoc Tu nhien Cdng ngh? vd .Mdi iru&ng. 29 (2013): 105-110
Tap chl Khoa hgc Tru'dng Dai hoc Can J\\0 website: sj. ctu. et^u. vn
NGHIEN ClTU iTNG DyNG HIEN TlTOTSfG NHIET HUYNH QUANG TRONG VIEC XAC DINH SAN PHAM CHIEU XA d VIET NAM Nguyen Duy Sang'
' Khoa Phdt triin Nong thon, Trucmg Dai hpc Cdn Tha Thdng tin chung:
Ngay nhgn: 23/05/2013 Ngay chdp nhdn: 24/12/2013 TUle:
Research on the application of ihermoluminescence phenomenon in determining irradiated products in Vietnam Tit khoa:
Nhifl huynh quang, phong xa, sdn phdm chieu xa, lieu chiiu Keywords:
Thermoluminescence, irradiation, product samples, radiation dose
ABSTRACT
Studying thermoluminescence (TL) phenomenon suggests the potential applications of this phenomenon in the radiation field, especially in identifying irradiated product samples in Vietnam. Determining the right radiation dose will help to check the safety of irradiated products in the market and to ensure the health oflhe consumers. This paper demonstrates the foundation oflhe irradiated product detection using thermoluminescence equipment in order to give more sufficient assessment on the application of this phenomenon in practice.
TOM TAT
Nghien ciru hien tirong nhiet huynh quang cho thdy tiem ndng img dung hien tirong ndy trong ITnh virc phong xa va dgc biet Id trong vi$c xdc dinh mdu chieu xg a Viet Nam. Xdc dinh dung lieu chieu se kiem chimg duac tinh an todn ciia sdn phdm chii u xg tren thi tnrang vd ddm bdo sire khoe cho ngirai tieu diing. Bdi viet ndy neu ra co sa cua viec xdc djnh mdu chiiu xa tren thiit bi nhiet hu)'nh quang nhdm ddnh gid day du han vi khd ndng irng dung cua hien tuong nhiet hm'nh quang tren thuc te.
\ D^TVANDE
Chiiu xa thyc phdm la mOt trong cac cdng nghe sir dung nang lugng cua tia phong xg co tinh biic xa ion hoa dl xii ly thyc pham nhdm nang cao chit lucmg vl sinh va an loan cho sin pham. Thyc phim, ndng san chieu xg di dugc chiing minh la lanh tinh vi raang lai nfaiing Igi ich kinh ll - xa hpi to Idn. Tuy nfailn, van de dat ra la bdng cdch nio di nhdn bilt dugc sdn phim da chiiu xg hay chua frong khi mdu chiiu xg vi khdng chieu xg khi quan sat fryc tiep khong khac gi nhau. Xuit phat tir nhu cau frln, phuang phdp nhilt fauynfa quang TL can dugc nghiin ciru va dp dung.
Trong nhiing nam gdn day, ITnh vyc TL dugc nhieu nghiin ciiu tren thi gidi quan tdm do nhiing ling dung thyc tien ciia no frong do lilu phdng xa, djnh tudi cic cd vat. xdc dinh kfauyit tit xdy ra
trong mang tinh thi. Phuang phap TL dp dyng len cdc mdu va da phat hiln rdng cac mau khdng bi chiiu xa co cic dinh pho TL rit tfaip trong khi cac miu da chieu xa cac dinh phd cao vi ting ddn theo liiu xa (Correcher et al., 1998). Day li phit hi|ri quan frpng frong viec xac dinh mdu da chieu xa. O Viet Nam, vdn di nay van chua dugc quan tam vi hiln chua cd nghiin ciru nao. Hien tai khu vyc pfaia Nara chi cd Vien Hgt nhan Di Lgt va Trung tira Hgt nhan TP.HCM co ddy du raiy radc phyc vy nghiin ciru niy.
2 GIAI QUYET VAN DE
TL Ii hiln tugng phat ra inh sing tir cac chit each diln hogc chdt ban din khi chiing dugc nung nong. TL thuc chit la sy phat sang vi nhiet khi elecfron ben frong vdt hip thu nang lugng biic xa.
Tgp chi Kboa hoc Tnr&ng Dqi boc Cdn Tba Ba >'eu td cin thiet cho vile phil tin hieu huynfa quang:
- Diu riln. vdt lieu bi kich thich nhilt phdi Ii chat ban ddn hodc chat cdch di|n, vit lieu li kim loai khdng phat ra tin hieu TL.
- Tfaiir hai. vat lieu phii cdn thdi gian dl hip thy nang lugng frong suot qua trinh phai chilu biic xa.
- Thii ba, vile phit tin failu TL can phii dugc khdi ddng bing sy nung ndng vat chat. (Hoang Due Tam et al., 2009).
2.1 Md hinh gidi thich cu che dpng hoc TL {McKeever S. W.S, 2000)
2.1.1 Mo hinh dong hoc bdc 1 -Mdhinh Randall Wilkins
Cdc qua trinh vgt li chl phdi hien tugng TL bit
Phdn A: Kboa hoc Tu nhien. Cdng nghe va Moi tnr&ng 29(2013): 105-110 ngudn til sy djcfa chuyin ciia cdc hat mang diln (elecfron va Id trdng) giiia cac raiic nang lugng dugc tao ra do sy sai khic vl rail cdu tnic tinh the - cac khuyit tat cua vat lilu. Hinh 1 Id so dd cau friic vimg nang lugng don gidn nfadt rad td hiln tugng TL. Vung ddn vd viing hda tn dugc tdch rdi ra bdi vimg cim. Bdy ndm frln miic cdn bang Fermi vd do vgy nd hodn toin frong rdng frong trang thii can bdng (ttiroc kfai hap thy biic xg). nd dugc gpi Id thi bay electron. Ngugc lai. tim tdi hop ndm ben dudi miic Fermi nen nd dugc chiim ddy cic electron va dugc gpi la thi biy Id frdng.
Vdi nang lugng biic xa hap thy (hv)a > Ec - Ey (Idn hon bi rpng viing cam) sl din din qya trinh ion hoa cdc elecfron hda fri tao ra cdc elecfron ty do trong vimg din va cde lo trdng ty do frong viing hda tri (djch chuyen I).
Viing dan
Hu>'nh quang (ftv)o _ Mirc can bang
Fermi E, Tam tai hgp
Hinfa 1: Gidn do nang lugng dl giai tfaiefa qud trinh cfauyin mire Kha ning tdi hgp fryc riip cac elecfron va lo
frdng qua vimg cira it xay ra hon tdi hgp giin tiip, nhat la ddi vdi chit bin ddn vd chat each dien co vimg cara rong. Vi viy qua frinh tdi hgp xiy ra.
diu tien cic Id trdng bi bay d tim tdi hgp R (dich chuyin 5). Sy tai hgp diln ra qua vile hiiy cac 16 frdng bi biy bdi cac elecfron ty do (dich chuyin 4).
Trong miu nay. nlu sy dich chuyen tdi hgp li do bdi biic xg thi qud frinh nay dugc xem la sy phat huynh quang.
Ngoii ra. cac elecfron ty do cung cd the bi bay tgi miic T (djch chuyen 2). Trong trudng hpp niy, sy tai hgp chi cd thi xiy ra. nlu electron bi bay hip
thu du ndng lugng (E) &h quay trd lai vung din.
Thdi gian sdng ciia elecfron vd Id tring la rdt ngin va no bi bit bdi cdc tim tuong iing (ngudi ta gpi mau luc ndy d frgng tbdi kich thiefa). Nhu vgy, qud frinh phit huynh quang sl cd thdi gian tri hoan bang thdi gian ciia cac electron trong biy, cd phuong trinh sau:
6 day p dugc dinh nghia la xac suit giii phdng elecfron khdi bdy do tie dpng nhiet, s: hi sd tin sd thoat CO thii nguyin giiy'. Y nghia yat li cua he sd nay: bay bit dugc xem nhu mdt hi thi dugc dac
Tap chi Klioa hoc Tnrdng Dgi hoc Cdn Tba Phan A • Klwa hoc Tu nhiin. Cong ngii? vd Moi Inr&ng 29 (2013/: 105-110 tnmg bdi he si tan si thodt s, s li tich ciia tdn sd va
chara dien hi vdi vach hd flii yd he so phan xa. Do vgy CO thi xera s co dp Idn bang tin sd dao dpng ciia mang tinh the.
Md hinh Randall Wilkins la md hinfa don giin nfait md ti dudng cong TL dugc dua ra vao nam 1945 tren ca sd cdu tnic vimg ndng lugng (xem Hinh I) dya fren hai gia thiit co ban sau:
Trong viing cim chi ton tgi rapt logi tam bat va tim tai hgp.
- Cac electron bi kich thich bdi nhilt va thoat khdi tira bit chuyin lln vung ddn vd tdi hop ngay vdi cac Id trdng frln tdm tdi hgp, chiing khdng bi bit trd vao cac bay hoac tdi hgp vdi cac tdm tii hgp.
Nhu vdy, ta cd the thay ring tdc dp giai ph6ng elecfron do nhilt bang vdi tdc dp tii hop.
Tdc dp gidi phdng elecfron do nhilt ti II vdi mat dp elecfron fren biy theo thdng kl Boltzmann. Phuang frinh mo ta sy thay ddi mat dp diln tii frln bdy dugc viet nhu sau:
dt~ {\-(7^)pn (2)
n la mat dp electron tren bay, <7^ la xac suit electron bi bit lai vio bay (frong md hinh Randall Wilkins O"^ = 0). Phuang frinh (2) vi vay dugc vilt lgi cd dang:
dri_
dt' (3)
Trong do: k la hing so Boltzraann; E la nang lugng kich hoat ciia bay bdt elecfron.
Khi nhilt dp ting, cac elecfron dugc giai phdng nhilu ban vd qud trinfa tai hgp xay ra lam gidm nong dp cac 16 frdng va lam ting cudng dp TL. Khi cac elecfron bay it dan, tdc dp tai hpp cung giam va theo dd cudng dO TL cung giira theo. Qui frinh nay tgo ra dinh TL ddc frung. Tfadng thudng, trong cdc thi nghiera loai nay, nfaiet dp tang theo ham tuyen tinh ciia thdi gian. Moi quan he nay dugc bilu diln dudi dgng:
T = T,^/3t (4)
0 diy P la tdc do gia nhilt ( = - ^ ) , To Id dT dt nhilt dp ban diu ciia mlu. Liy tich phdn tir / = r^.
vdi dieu kiln &hi T = TQ, n phuong trinh (4) cho kit qua:
I{T) = t%se' (slp)]e
m, ket hgp vdi
(5) Day la phuong frinh md ti cucmg do ddng nfaiet phat quang theo md hinh Randall Wilkins fade nhdt.
Dudng cong nhiet phat quang riiin flieo co chi dpng hpc b$c nhdt nay cd tinh bdt doi xirng: sy suy giam cudng dp nhilt phat quang img vdi mien nhiet dp 7" > Tmax doc hon phan cudng dp phdt xg tang ling vdi T< T^ai
2.1.2 Mo hinh dong hoc bdc 2 - Mo hinh Garlick Gibson
Theo md hinh Garlick Gibson: Cac hgt mang dien cd thi bi bit trd lgi vdi xic suit bit lgi bdng xac sudt tdi hgp. Hinh 2 minh hpa cfao md hinh dpng hpc bac hai. Elecfron bj kich thich do tdc nhan nhilt dO chuyin lln vimg din (chuyen djch 1). Chiing CO the tdi hop vdi Id trong trin tdm tai hgp (chuyen djch 3) kem theo phat huynfa quang vi cd thi bi bit lai vao tdm bat (chuyin dich 2).
Vung din
Vung hoa tri
Hinh 2: Gian d i mo ta cfauyin dpng bac hai vd tdng qudt
Theo rad hinh ddng hpc nay, trong riydng hgp die bill, xdc suit bit frd lgi bdng xac sudt tdi hgp, khi do:
Hay I(t) = dn
"dt'
(6)
(7)
Tap chi Klioa hoc Truang Dai hgc Cdn Tha
Trong dd .^' Id mat dp bdy, s' ciia phuang trinh (7) cd dgng:
Plidn A: Khoa hgc Tu nhien. Cdng ngW vd Mm bvong: 29 (2013):
= — , Nghiem
](T) = n:,s'e'^/ \-\-{n^s'/p)\e'^dT
Tt
(8)
Dieu kien cyc dai ciia bieu thirc (8)
^dT)
- 0 , tir day ta cd;\+(r^^'/P)\e ^dT
\
-QkT^n^'lPE^'
Tu nhirng phuang trinfa treiL cfaung ta cd nfaan xet nfau sau: frong bieu tfauc (9) cd sy xuat hiln ciia nrj — ndng dp ban dau ciia cic electron trong cac bay. dieu ni>' cd n ^ a rang \ i tri dinh nhiet phdt quang T„ai thay ddi theo ndng dp cua cic elecfron frong cac bay. Khi no nhd. vi tri ciia dinh nhilt phit quar^ se nam d nhilt dp cao hon so vdi kfai rio Idn {Furetta C. 2003).
150 Nfaiet d6 (HTl
Hinh 3: Dudng cong tfaeo mo hmh bgc 1 dugc tinh vdi E = I,OeV, 5=10'" s^' va p = iCC/phdt Dirdng cong bgc nfaat nay dirge tinfa vdi ndng dp fagt mang dien ban ddn la: (1): 1,0; (2): 0,8; (3): 0,6; (4): 0,4;
(5): 0^ va (6): 0,05 (dom vi chung la 10^ hat tren m^)
150 200
^ndet do (•Ct
Hinh 4: Dirdng cong theo md hinh bac 2 dtrgc tinfa vdi E = l,OeV, s=W s"' va p = lO'C/phut Dinmg cong bac hai nay dugc tinh voi noog dp hat mang dien ban diu la: (1): 1,0; (2): 0,8; (3): 0,6; (4): 0,4;
(5): 0,2 va (6|: 0,05 (don vj cbuDg la 10^ hat tren m^)
Top chi Khoa hoc Tnr&ng Drji hoc Can Tho Phdn.4 Khoa hiK Tunhien. Cong ngbe vd Mdi inr&ng 29l20l3i 105-110 So sinfa cdc dudng cong nay frong hai nordng
hgp su dyng md hmh bgc nhit vd rad hinfa bdc hai ta thdy ring cac dinh TL frong trudng hgp bac nhat khong dich chuyin theo nhilt dp frong kfai d riirdng fagp bac faai, dinfa TL djcli chuyin vi phia nhilt dp cao khi «ocang nhd - diiu nay cho thdy sy phy thupc ctia duih TL tiieo no. Ngoai ra, cdc dinh TL trong tnrdng hgp bac hai cd tinh ddi ximg theo true thang dimg tdt han so vdi trong trudng hop bic nhat.
Nhu vay, cd thi thiy nlu xac dinh dugc lugng TL phdt ra thi cd thi xic djnh dugc liiu biic xa ion hda da cfaieu len mdu. Day chinh la co sd ciia ky thuit do liiu bing phuang phap TL trong viec xac djnh raau dd chilu xg.
2.2 Do tin faieu TL
2.2.1 Chudn hi vd xir ly mdu diing cho kv thudt TL
Mdu thuc pfaim phii hgp cho ky thugt TL nhu cic logi thao mdc, gia vi, rau cii, ngu coc, ddng vat cd vo va cdc logi frii cay co chiia kfaodng chit silicat. Vile chpn cac mau thyc phim cho nghien ciiu TL dya fren kha ndng chia tdch liln quan din thdnh phan vo ca cua mau. Nguyen ly lam viec ciia thiit bi TL gan liln vdi thyc nghiim vol vile chuin bi mdu, do lilu hap thu, each ly cac thanh phan v6 CO va viec chuan hoa do ludng TL .
Cac mau thyc pham dugc thu mua tir cdc chp sau do dugc ddng gdi frong tiii nhya vd dugc chia thdnh timg Id nhd. Mpt frong so chiing khdng chiiu xa, sd cdn lgi dugc chieu xg vdi biic xa gamma theo tiiu cfaudn. Viec chilu xa mau cd thi diing raiy Cobalt-60.
Tiiy theo mdu ma ta xir ly nhiet thich fagp, cac mdu tfayc pfadra nhu liia, giing, khoai tdy, cu nghe c6 the giii d nhilt dp raoi tnrdng (27± 2''C), vdi cac sin phdm ddng Ignh nfau tdm can bao quin d nhilt dp Ignh (0±4^C).
2.2.2 Nguyen li chung ve do tin hieu TL Liiu ki TL lira viec bdi sy nung nong vit lieu TL vd do ludng anfa sang phat ra tir birc xg phdton thdng qua qui frinh kich thich biy elecfron d viing cdm cua tinh thi. Cac mdu chilu xa dugc dat frln gia nung vd dugc dun ndng thong qua bp nhilt di|n. Anh sdng phat ra dugc cho di qua bO lpc hogc thiit bi tach sdng nai raa dugc xu ly d^h chuyen doi tan sd song phdton phit ra sang dang ph6 nhin thay noi ma sau dd thu nhin thdng qua thilt bj nban quang (PMT). Ddu ra cua thiit bi PMT dugc tich hgp frong mdt bo rich fagp. PMT dugc diing &z
cfauyin doi thdng lugng dnh sing phdt ra tir vat lieu TL sang tin hieu dien Hi. Nhiing ph6ton tuong tie vdi am cyc quang, noi ma ndng lugng tir nhiing ph6ton dupe hap thu fruyin cho am cyc quang vd chuyen d6i thanh elecfron. Elecfron ty do di chuyen vi thoat khoi bl rait. Dong elecfron sau dd dupe gia tdc den duang cyc pfau dau. Duong cyc phy dugc thiet ke sao cho ndng lugng tap frung ciia mdt chiim elecfron se cho kit qui trong sy phat ra nhieu hon mot elecfron tir be mdt ciia duong cyc phy. Ong nhan quang cd khoang 10 duong cyc phu, sau khi khulch dai trong khoang giiia duong cyc phy, elecfron dugc thu nhan d duong cyc vi rin hieu elecfron dugc xii ly. So dd b6 fri he thong do TL dugc chi frong Hinh 5 (Jensen, 1997)
Hinh 5: So do nguyin Ii he do TL 2.2.3 Mot so ket qud nghien cuu vdi thiet hi TL Lin dau rien phuong phap TL dugc su dung trong cac miu san phdm nhu gia vi. thio dugc, cfad la (Sanderson et al, 1989; Khan vi Delincee, 1995). Khi tiin bdnh nghiin cim xic dinh mlu chiiu xa vdi liiu chilu tdng dan 1 kGy, 5 kGy, 10 kGy, 18 kGy, 21 kGy. nhan thiy cic man kfadng chieu xa dinh phd TL rat thdp frong khi cic raau da chiiu xa cac dinh phd cao va tdng ddn theo lieu xa (Correcher et ai, 1998). Tin hieu TL se glim di niu thdi gian keo dai qua nhilu thing (Autio va Pinnioja, 1990). Nam 2001, Atta vd cdng sy da nghien cim chiiu xa tren thit gd vi ca bing kJ thuit TL, cac miu dugc chiiu xa bdi nguin gamma Cobalt-60 voi liiu hip thu 1,2. 3, 4, va 5kGy. Mau dupe chiiu xg va khong chiiu xg d khoing nhilt SO^C din SOO^C dugc do bing tfaiit bj TL cd toe dp gia nhilt 10°C/s, gia fri ting ddn vdi nhilt dp va dat cyc dai d I95''C cho moi trudng hgp. Cudng dp TL phy tiiupc vio liiu hip thy va gia tdng theo lilu hap
Top chi Khoa hoc Tru&ng Dm hgc Cdn Tho Phdn .4: Khoa hgc Tu nhien. Cdng nghi vd Moi tru&ng: 29(2013) 105-110 thy. Nim 2011, Sanyal di tiln hdnh nghiin ciru xic
dinh chilu xg tren mdu Id hot t6m vd dat dugc nhilu kit qua khi quan, vdi lilu chieu 2kGy cd sy phan bill khi ro rang giira miu chilu xg va khdng chilu xg nhung cic dinh chilu xa chiu inh faudng bdi nfaiet dp: dinfa cao nfait d dp cao khoang 225**C (Hinh 6). Kfai thay doi lilu chieu kit qua thu dupe cua nam mau sin phira, frong dd, san pfaim kfadng chilu xg CO phd nim d vi fri thdp nhit, cic miu khac dinfa pho cao ddn tfaeo lieu chieu (Hinfa 7).
A
• * SCEC
I'
J ,
liiuei do I=C}
Hinfa 6: Dinh T L t h a y ddi t h e o nhiet dp
IkGy akoy 3kGy 5kC^
r-n^.
Ll
Hinh 7: Dinfa TL tang theo lilu chieu 3 KET LUAN
Nghien cim cho tfaiy viec van dung phucmg phip TL de xac dinh sdn phara chieu xa la rdt khi quan. Kit qui nghien ciiu cfao thiy 6 rapt s6 nudc fren the gidi da ip dung phuang p h ^ niy frong vile xac dinh chilu xa va mang lai nhieu thinh
cdng. Vi viy, vi|c van dung phuong phdp nay la cin thiit d nudc la, giiip minh chiing dp an to^an cho cic sin phira, thyc pfaim di chiiu xa tao nilra tin cho cpng ddng kfai su dyng.
TAI Ll£U THAM KHAO
1. AliaSA,SattarAA,AhmadAI.NagraSA, Ahmad T. 2001. Suitability of tfaermoluminescence for the detection of irradiated chicken and fish. J Radioanalyt Nucl Chem 250(3 ):537-40.
2. Autio T, Pinnioja S. 1990. Identificarion of irradiated foods by the thermolurainescence of raineral contaminarion. Z Lebensm UntersForsch 191:177-80.
3. Correcher V. Munlz JL, Gomez-Ros JM.
1998. Dose dependence and fading effect of the thermoluminescence signals in gamma- irradiated paprika. J Sci Food Agric 76:149-55.
4. Furetta C. 2003. Handbook of Therraoliuninescence. Physics Department.
Rome University. Italy
5. Hoang Due Tam, Thai Khac Dinh, Nguyen Quang Mien, Bui Van Loat. 2009, The thermoluminescence characteristics of LiF (Mg,Cu,P) in measuring gamma ray by the RGD-3A reader. Advances in optics photonics specfroscopy & Applications V, pp. 719.
6. Jensen LB. 1997. Luminescence techniques:
instrumentation and methods. Radiation Measureraents 27(5/6):749-68.
7. Khan HM, Delincee H. 1995. Detection of irradiation treatment of dates using thermoluminescence of mineral contaminants. Radlat Phys Chem 46:717-20.
o. McKeever S.W.S. 2000, Thennoluminescence of Solids, Cambridge University, England.
9. Sanderson DCW. Slater C, Cairns KJ. 1989.
Detection of irradiated food. Nature 340:23-4.
10. Sanyal B. 2011, Studies on detection and dosimetry of irradiated food by thermoluminescence (TL) and electron pararaagneric resonance (EPR) specfroscopy. Food Technology Division, Bfaabba Atomic Research Cenfre, India.
