VNƯ Journal of Sciciicc, M athematics - Phvsics 24 (2008) 97-100 Thermoluminescence properties o f LÌ 2B :Cu material N go Q uang T h a n h '’*, Vu X uan Q uang“, N guyen The Klioi^, N guyen Dac Dien'^ ^Yen B Teacher T raining C ollecge, 53 group, D o n g Tam award, Yen Bai City, Yen B province, Vietnam ‘^ In stitu te o f M a teria ls Science, VAST, 18 H o a n g Q uoc Viet road, Call G iay Dist., H anoi, Vietnam ^F a c u lty o f Physics, H a N o i U niversity o f Education, X u a n Thuy street, Can G iay Dist., H anoi, Vieinarn '^Cau G iay C oĩỉíữníous E ducation Center; N o 2, 233 branch, X uan T huy street, Cau G iay Dist., H anoi, Vietnam Rcccivcd 10 April 2008; rcccivcd in revised form 25 June 2008 A b s t r a c t The coppcr-doped lithium tetraborate LÌ2 B 407 :Cu (LBCu) is one o f the famous tissue equivalent materials for the thcrmolumincsccnt dosimetry, very useful for applications in mcdical and personal dosimetry measurements This material in powder and pellet forms was prepared by sintering method in the Laboratory o f A pplied Spcctroscopy and Geinology[MS-VAST In tlùs study the dositnclric characteristics o f LBCu powder were examined: hom ogcneitv o f batch, reproducibility, dose response and evaluation kinetic parameters K eyw ords: Lithium Iclraborate, Thermoluinincscent, Dosimetry Introduction T he coppcr-dopcd lithium tetraborate LÌ2B4 :Cu (LBC u) is one o f the w ell-know n m aterials for thennolum incsccnce dosim etry w ith cfFcctive atom ic n u m b er Z e //= clo.sc to th at o f soft biological tissue T his m aterial has h id i sensitivity, linear dose dependence, a w id e operation dose range, and a w eak dcpcndcncc o f the ionizing radiation energy LBCu is very pro m isin g m aterial for applications particularly in m cdical and personal dosimetry T he first th em io lu m in escen t m aterial based on lithium tetraborate activated b y m anganese is com m ercialized by H arshaw u n d er the nam e T L D -800 This m aterial p resented a very poor sensitivity, m ainly caused by th e light em ission in the 600 nm region o f the spcctra, far from the response region o f m ost o f the photom ultipliers used in com m ercial rcader The u se o f copper as activator instead of m anganese overcom es the draw back o f poor sensitivity, shifting th e em ission spectrum to about 370 nm [1, LBCu m aterials in p o w d er and p ellet fom is have been prepared b y sin terin g and m elting m ethod in the Laboratory o f A pplied S pectroscopy and G em oloey-IM S-V A ST T h e LBCu sam ples w ere iưadiated w ith gam m a source or X -ray tube copper anticathode at 25 kv, m A T heniially stim ulated lum inescence (T S L ) m easurem ents w ere carried out on the H arshaw M odel TL D 3500 Reader * C orresponding author E -m ail; thanhnq@ im s.vast.ac.vn Q7 Ngo Quang Thanh et a i / VNƯ Journal o f Science, Mathematics ~ Physics 24 (2008) 97-Ỉ00 98 R e s u lts a n d d isc u ssio n 2.1 P reparation a n d o p tim iza tio n T he LB C u po w d ers [2, A], and p ellets [3, 5] w ere prepared b y sintering m ethod Ethanol solution o f C uC l2 w as m ixed w ith sto ich io m etric am o u n t o f com m ercial L Ì2B4 O The dispersion w as hom og enized b v stirring th e m ix tu re fo r 30 niin, u sin g a m agnetic stiư er A fterw ards alcohol w as allow ed to evaporate a t am b ien t te m p eratu re D ty in g w as com pleted in a laborator)' flim ace at 100 ""C for 10-12 hours T he pellets (4.5 m m in d ia m e te r and 0.95 m m in thickness) w ere th en prepared b y cold pressing th e as-prepared LBCu p o w d ers P o w d er and p ellets w ere k ep t in a p la tin u m crucible and sintered at 870 ° c for 30 m in in air atm osphere, follow ed b y a n a tu l c o o lin s to room tem perature P ow der w as then eround and sieved to obtain erain size in th e range o f -2 0 fim , and the obtained p o w d er w as th en heated asain at 400 "C fo r Ih ^^0,005% M 0,^% M 0J25% M — D oj ^ 0, I5%M 7000 3,0x10 - Imax Response 2.5x1 o " - -5000 Ừ) 0,2% IVl M V -6000 U ÍÍ 2,0x10®- 4000 _l Ư) 1.5x10®- Ị-3000 \ ’l.0x10®5,0x10 = 2000 1000 855 060 865 870 875 880 885 890 895 900 50 100 'Ĩ S 200 ^ 250 300 350 Temperature ( °C) Temperature ịc) F ig TSL glow curve o f L B C ii sam ple as a function o f Cu concentration Fig M axim um peak intensity and rcspoase o f LBCu sample versus sintering temperature T he sintering te m p eratu re and Cu co n cen tratio n are im portant p aram eters w h ich influence TSL p roperties o f the m aterial F ig u re and show th e T S L -response as a flinction o f Cu concentration and sin te rin g tem p eratu res It can b e seen th a t th e T S L -response increases grad u ally w ith increasing copper concentrdtion and sin te rin g tem p eratu re w ith in the range from 0.1 to 0.15 m ol% and from 870 to 880 °c respectively A b o v e th e se tem p eratu res th e sam ples u n deigo a com plete m eltine and the T S L signal can not be co llected again A t th e tem perature 890 the optim al tem perature o f sinterins: p ro cess is 870 °c, sam ples w ere m elted Therefore, °c for copper concentration o f 0.15 mol% 2.2 H o m o g en eity E valuation o f th e h o m o g e n eity w as caư ie d out w ith 10 sam ples taken from a given batch and irradiated at the sam e rad iatio n dose T he m aterial exhibiting standard deviation about % could be accepted fo r the d o sim etric ap p licatio n Mgo Quan^ Thanh et al / VNƯ Journal o f Science, M athematics - Physics 24 (2008) 97-Ỉ00 99 EvcPy’ batch o f m ore than e in wciiih has to be h o m o g en eity tested T he resultant TSL response w as betw een 2.0-3.0 % variations based on standard d ev iation o f 10 seq u en tial m easurem ents A c cording to th e ev alu atin g o f the R adiotherapy Laboratorv^ in Hcnr>' M o n d o r H ospital, our dosim eters show a standard deviation o f 2.25 % 2.3 R e p w d u c ib ility T he T S L sen sitiv ity o f sam ple T4 is alm ost un ch an g ed a fte r 10 tim es o f th e TSL reading out T he fluctuation o f the T S L intensity w as estim ated ab o u t 3.6 % It in d icates th a t LBCu is the reusable m aterial in th e d o sin ictric application 2.4 TSL d o se response T he dose response w as chocked by H enry M ondor h o sp ital T h e resu lts o f the m easurem ents show a linear dose response in th e study raníỉe o f dose u n til 30 G y (show in iig.3) ^ 5X10 I 3X10‘ ■E 10 15 i>0 Gamma Dose (Gy) Fig TSL response of the main glow peak versus giimina ray dose 2.5 E valuation o f the kin etic p a m eters Some selected T S L glow curves o f sam ple afte r iư a d ia tio n o f d ifferen t dose levels are show n in fíơ.4 T he glow curve show s peaks in the range from 50 to °c T he tem perature o f every peak in th e glow curve o f LB C u does not shift w ith in creasin g dose levels T h is m eans th at all o f the glow peaks in th e investigated region ought to be o f th e first- o rd er o f T S L k in etics T he variable h eatin g rate m ethod consists o f m o n ito rin g a glo w p eak tem perature w ith different heatm g rates In accordance w ith the m ethod, the te m p eratu re T m d ep en d s on the heating rate /3 this dependence can b e defined b y the follow ing equation: ỉn ự llíĩ) = EjkTm + ln{Elks) w here ( s “ ’ ) is th e frequency factor, E (eV) is th e trap d ep th , T m (A ') is th e m axim um tem perature o f the elow -pcak and k is B o ltzm an n ’s constant I f Tm is m sasu red fo r a n u m b er o f different heating rates E can be found from th e slope o f the straight line obtained from the p lo t o f the logarithm ic term /n (T ^ /3) ag ain st Xj Tm- The value o f s can also b e obtained from th e in tercep t o f the slope Figure 100 Ngo Quang Thanh eĩ a i / VNƯ Journal o f Science, Mathematics - Physics 24 (2008) 97-ì 00 2,5x10 1.5x10® 2,0x10 - 1,0x10 1.5x10 ró _J Ư) *“ 5,0X10*- 100 150 200 2S0 300 350 400 1.0x10®- 450 50 Temperature ( C) 100 150 200 250 300 350 400 450 Temperature'^C) Fig The TSL glow curvc o f LBCu w ith different Xray irradiation tim es (at a heating rate o f Fig G low cu w e s o f LBCu measured at various healing rates Table A ctivation energy E and frequency factor s arc obtained using the variable heating rate method Peak Energy (eV) Frequency factor (s 0.43 1.3x10^ 0.98 7.3x10^ 1.17 4.1x10^ 1.46 x l0 ’° ) show s T S L glo w curves o f LB C u irradiated x-ray at various h eatin g rates and obtained results arc presented in tab le Conclusion The L ithium tetrab o rate doped w ith copper in pow der and p ellet fom i w ere prepared by sintered m ethod F or th e p rep aratio n o f th is dosim eter the optim um sin terin g tem p eratu re w as 870 ° c and the optim um concen tratio n o f Cu w as 0.15 m ol% T he hom ogeneity from b atch to batch w as accepted to dosim etric applicatio n T he reu sab ility o f the dosim eters has been investigated fo r nearly 10 repeated readouts u sin g th e read o u t anneal, w ith no change on the T S L response R epresented d o sim etric characteristics m ake sintered solid lithium tetraborate dosim eters very prom ising and su g g est poten tial use in different TSL d osim etry ap p lications, particu larly in medical dosim etry, and also fo r individual m onitoring R eferences [1] [2] [3] [4] [5] M Takenaga et aL Thermoluminescent material United States Patent, 4248731 (1981) R, Visocekas, s, Lorrain, G Marinello, Nucl Sci J 22 (1) (1985) 61 G Kitis, c Furetta, M Prokic, V Prokic, J Phys D: AppL Phys 33 (2000) 125 S Lorrain, J.R David, R Visocekas, G Marincllo, Radial Prot Dosim 17 (1986) 385, M Prokic, R adial Meas 33 (2001) 393 ... Temperature'^C) Fig The TSL glow curvc o f LBCu w ith different Xray irradiation tim es (at a heating rate o f Fig G low cu w e s o f LBCu measured at various healing rates Table A ctivation... h eatin g rate m ethod consists o f m o n ito rin g a glo w p eak tem perature w ith different heatm g rates In accordance w ith the m ethod, the te m p eratu re T m d ep en d s on the heating... concentration o f 0.15 mol% 2.2 H o m o g en eity E valuation o f th e h o m o g e n eity w as caư ie d out w ith 10 sam ples taken from a given batch and irradiated at the sam e rad iatio n