EXTINCTION COEFFICIENT USED AS PARAMETER IN GAMMA-RAY DOSIMETRY

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1 EXTINCTION COEFFICIENT USE AS PARAMETER IN GAMMA-RAY OSIMETRY C. POSTOLACHE Hor Hulue Ntonl Insttute for Nucler Physcs nd Engneerng, P.O. Box MG-6, RO Buchrest-Mgurele, Romn E-ml: Receved July 17, 017 Astrct. In ths pper, the vrton of the extncton coeffcent s result of the exposure to gmm-ry ws studed. The mterl used n ths study ws BK-7 type glss. Severl smples were exposed to gmm-ry Co-60 n order to otn dfferent sored dose vlues. By usng photo-spectrometrc mesurements, dfferent extncton coeffcent vlues s functon of the sored dose, were otned. The results showed tht the dependence of the extncton coeffcent to the sored dose presents lner regons, whch me t quntty tht cn e used n gmm-ry dosmetry. Key words: extncton coeffcent, gmm-ry dosmetry, sored dose. 1. INTROUCTION The mn optcl phenomen producng when lght reches mterl re trnsmsson, reflecton nd sorpton [1 4]. By mesurng these three prmeters usng photo-spectrometrc technques, quntfcton of other mportnt secondry optcl prmeters cn e otned [5]. It ws demonstrted tht the propgton speed nd the other chrcterstcs of the electrc feld crred y n electromgnetc feld depend to the propertes of the pssng thru mterls [6 9]. In ths pper, the vrton of the extncton coeffcent s result of the exposure to gmm-ry ws studed, strtng from hgh qulty photo-spectrometrc mesurements [10 14]. The extncton coeffcent s n optcl prmeter whch mesures the sorpton of lght n medum nd t s represented y the mgnry prt of the complex ndex of refrcton. When the lght s pssng thru medum, some prt of t s ttenuted, fct tht cn e expressed y defnng complex refrctve ndex, Equton 1: n n 1 Romnn Journl of Physcs 6,

2 Artcle no. 905 C. Postolche In Equton 1 the rel prt n s the refrctve ndex nd ndctes the phse velocty, whle the mgnry prt s clled the extncton coeffcent nd ndctes the mount of ttenuton when the electromgnetc wve propgtes through the mterl [1]. The phse velocty of wve s the rte t whch the phse of the wve propgtes n spce. Both n nd re dependent on the frequency. In most cses > 0 lght s sored or = 0 lght trvels wthout loss. In some specl cses, especlly n the gn medum of lsers, t s lso possle tht < 0, due to n mplfcton of the lght. The rel nd mgnry prts of the complex refrctve ndex re connected through the Krmers Krong equtons [15 0]. The mterl used n ths study ws BK-7 type glss, severl smples eng exposed to gmm-ry n order to otn dfferent sored dose vlues. fferent extncton coeffcent vlues, s functon of the sored dose, were determned. The results showed tht the dependence of the extncton coeffcent to the sored dose presents lner regons, whch me the extncton coeffcent quntty tht cn e used n gmm-ry dosmetry [1, ].. MATERIALS AN METHOS A numer of ten BK-7 type glss smples of 10 mm thcness were exposed to Co-60 gmm-ry source men energy of 1.5 MeV, nsde n rrdton chmer, n order to otn dfferent sored dose vlues Fg. 1. Fg. 1 Asored doses n the exposed smples.

3 3 Extncton coeffcent used s prmeter n gmm-ry dosmetry Artcle no. 905 A constnt dose det of 6. Gy/h ws used. The otned doses vlues were plced etween 0.04 Gy nd 1.0 Gy. For the mesurements of sored doses, n ECB ethnol-chloroenzene dosmeter system wth n verge mesurement uncertnty of.5 % for coverge fctor = ws used. After the exposure of the smples, hgh qulty photo-spectrometrc mesurements were performed [3 7]. 3. RESULTS AN ISCUSSIONS The vrton of trnsmtted lght ntensty thru the rrdted glss smples s functon of the sored dose s shown n Fg.. As t cn e seen, the trnsmtted lght ntensty s decresng wth the ncrese of the sored vlue. The fct tht trnsmtted lght ntensty s decresng wth the ncrese of the wvelength cn e lso seen, due to the fct tht hgher wvelength mens lower frequency. A lower frequency mens lower energy trnsported y the nvolved electromgnetc wve, whch leds to hgher sorpton when trvelng thru volume of mterl. Fg. Trnsmtted lght ntensty I tr. s functon of sored dose.

4 Artcle no. 905 C. Postolche 4 : Extncton coeffcent vlues were determned usng the followng Equton I ln 4 x I 0 tr., where: λ used wvelength; I tr. trnsmtted lght ntensty thru exposed glss smples for the specfc λ wvelength; I 0 ntl ntensty of the lght source; x smple thcness 10 mm. The nlytcl expresson of the vrton of extncton coeffcent s functon of the sored dose hs the followng form 3:, 3 4 where: λ used wvelength; the extncton coeffcent for n sored dose vlue, for the specfc λ wvelength; sorpton coeffcent for n sored dose vlue, for the specfc λ wvelength. The sorpton coeffcent ws determned usng Equton 4: 1 I 0 ln, 4 x I tr. where: λ used wvelength; I tr. trnsmtted lght ntensty thru exposed glss smples for the specfc λ wvelength; I 0 ntl ntensty of the lght source; x smple thcness 10 mm. The vrton of the extncton coeffcent s functon of the sored dose s presented n Fg. 3. An ncrese of the extncton coeffcent vlue wth the ncrese of the sored dose nd wth the decrese of wvelength cn e seen. In Fg. 3 t cn lso e seen tht the slope of the dependence etween the extncton coeffcent nd the sored dose, showng the speed of chnge, s decresng wth the ncrese of the wvelength, menng tht y usng lower wvelength, the senstvty of the method s ncresng [8, 9].

5 5 Extncton coeffcent used s prmeter n gmm-ry dosmetry Artcle no. 905 Fg. 3 The extncton coeffcent s functon of sored dose. Snce the dependence of the extncton coeffcent to the sored dose s lner on certn sored dose ntervls [ ] Gy, s t cn e seen n Fg. 3, t cn e used successfully s prmeter n gmm-ry dosmetry. The expresson of the dependence etween the extncton coeffcent nd the sored dose s otned y fttng the expermentl dt, ts generl form eng presented n Equton 5: log, 5 where: extncton coeffcent for n sored dose vlue, for the specfc λ wvelength; ndex 1,, 3 correspondng to used wvelength 475 nm, 490 nm, 530 nm. The generl form of the Error Propgton Lw [30 3] ppled to Equton 5 s presented n Equton 6, s follows:

6 Artcle no. 905 C. Postolche 6. 6 The generl form of the Error Propgton Lw ppled to Equton s presented n Equton 7, s follows:.3 log. 7 By nlytcl clculus, the Equton ecomes Equton 8, s follows: The Equton 8 s prctclly the generl form of the dependence of the sored dose vlue to the vlue of the extncton coeffcent. By usng ths expresson, n unnown sored dose vlue cn e determned, only y determnng ts correspondng extncton coeffcent vlue. The generl form of the Error Propgton Lw ppled to Equton 8 s presented n Equton 9, s follows:. 9 The concrete form of the Error Propgton Lw ppled to Equton 8 s gven y the Equton 10, s follows: log All the qunttes from Equton 10 re nown, Tle 1. The Equton 10 represents prctclly the uncertnty ssocted to the method presented n ths pper. By fttng the extncton coeffcent s functon of the sored dose vlue, the clrton curves were otned, s t cn e seen n Tle. By usng them, n unnown sored dose vlue cn e determned.

7 7 Extncton coeffcent used s prmeter n gmm-ry dosmetry Artcle no. 905 The sored dose rnge [Gy] Tle 1 The fttng prmeters nd ther ssocted uncertntes Wvelength [nm] Fttng prmeters σ σ * * * Tle Asored dose vlue s functon of extncton coeffcent for 475 nm, 490 nm nd 530 nm wvelengths Asored dose vlue [Gy] ependng of wht wvelength s used for determnng the extncton coeffcents, one of the three clrton curves from Tle cn e used s follows: the frst one s vld when 475 nm lght source s used, the second one when 490 nm lght source s used nd the thrd one when 530 nm wvelength s used. All three clrton curves from Tle re vld only on dose rnge etween 0.16 Gy nd 1.0 Gy. 4. CONCLUSIONS As t ws shown n ths pper, the exposure of optcl glss to gmm-ry leds to modfctons of ts prmeters, such s ts extncton coeffcent. The vlues of the extncton coeffcent were determned for ten BK-7 glsses exposed to gmm-ry, y usng photo-spectrometrc mesurements. As t ws shown, the extncton coeffcent cn e used s dosmetry prmeter, snce ts dependence to the ncrese of the sored dose s lner on certn ntervls.

8 Artcle no. 905 C. Postolche 8 It ws shown tht the slope of the dependence etween the extncton coeffcent nd the sored dose s decresng wth the ncrese of the wvelength, menng tht y usng lower wvelength, the senstvty of the method s ncresng. The nlytcl expresson of the vrton of extncton coeffcent s functon of the sored dose ws otned. The expressons otned for the dependence of extncton coeffcent to the sored dose represent the clrton curves, vld on dose rnge etween 0.16 Gy nd 1.0 Gy. By usng them, n unnown sored dose vlue cn e determned. The useful doses rnge cn e extended y usng dfferent types of glss, dfferent smples thcnesses nd dfferent wvelengths. Usng the uncertntes propgton lw, the uncertnty ssocted to the method ws determned. Acnowledgements. Ths wor ws supported y the Project ELI-RO 13/016 from Mnstry of Reserch nd Innovton of Romn. REFERENCES 1. E. Hecht, Optcs, 4 th Edton, Edtor Person Addson-Wesley, Sprng, Austn, G. I. Kozn, Physcs Proced 73, , do: /j.phpro P. Hrhrn nd P. Hrhrn, Bscs of Interferometry Monochromtc Lght Wves, nd Edton, Sydney, 007, do: /B / M.-R. Ion, I. Gru, P. Ion, M. Bclum, G-V. Ion nd C. Gvrl, J. Optoelectron. Adv. M , M. R. Ion, I. Gru, G. V. Ion, L. Rusen nd P. Ion, J. Optoelectron. Adv. M. 16 1, X. Fu, L. Song nd J. L, Journl of Rre Erths 3 11, , do: /s X. Fu, L. Song nd J. L, Nucl. Instrum. Meth B. 330, , do: / j.nm J. u, J. Wu, L. Zho nd L. Song, Rd. Phys. Chem. 86, , do: /j.rdphyschem K. Kdono, N. Itur, T. A, M. Ymsht nd T. Yzw, Nucl. Instrum. Meth B , , do: /j.nm M-R. Ion, Rom. J. Phys , M-R. Ion, Opt. Commun. 369, , do: /j.optcom M-R. Ion, Rom. J. Phys , M-R. Ion, Rom. J. Phys , M-R. Ion, Rom. J. Phys , L.X. M, J.Y. Tn, J.M. Zho, F.Q. Wng, C.A. Wng nd Y.Y. Wng, J. Qunt. Spectrosc. Rdt. Trnsfer. 196, , do: /j.jqsrt W.A. Rmdn, H.H. Wh nd M.A. Shms El-n, Opt Fer Technol 36, , do: /j.yofte

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