Alexander Kudin Protective Coating on the Surface and Characteristics Stability of Scintillators Based on CsI Crystal at Natural and Radiation Aging Institute. - презентация

1 Alexander Kudin Protective Coating on the Surface and Characteristics Stability of Scintillators Based on CsI Crystal at Natural and Radiation Aging Institute for Scintillation Materials NAS of Ukraine Kharkov, Ukraine

2 Radiation hardness of CsI pure crystals 2 Induced absorption of CsI crystal as a function of irradiation dose (N. Shiran, 1997). Arrows show a critical dose for crystals used in present work Critical Doze, Rad 10 5 – N.Shiran, et al, 1997; 10 6 – A.Smacula et al, 1960; 10 7 – I.Garapyn, et al, 2007; 10 2 – A.Kudin et al, 1997; 10 4 …10 5 – C. Woody (Horiba and Bicron Crystals) Critical Dose Dose [Gy] k i – k o [cm –1 ] Woody C.L., Levy P.W., Kierstead J.A. Readout techniques and radiation damage of undoped cesium iodide. IEEE Trans. Nucl. Sci. 37, 2 (1990) 492.

3 3 Ease mechanism of radiation defects creation OH – = O – + H o H° + CO 3 2– + V a + = HCO 3 – + F 1730 cm –1 in IR spectra 790 nm in absorption spectra Radiation hardness of large CsI pure crystals (ISMA) Commercial crystals – Rad Best crystals – Rad ;

4 CsI:Na Gektin A., Shiran N., Kudin A., et al, Role of vacancy defects in luminescence of CsI. Optics and Spectrosc. 72 (1992) Living Layer (LL) in CsI:Na Crystals Explanation Sliding of dislocations results in formation of vacancy dipoles V C – - V A +. New luminescence centers increase the blue band ( = 430 nm, = 3 s) of CsI:Na crystal ( =420 nm, = 0.63 s). Kudin A., et al, Scintillation response of CsI:Na and CsI:Tl to excitation by soft X-rays. Problems of Atomic Science and Technology 4 (2001) 111.

5 P Pl ~ 50 … 80 g/mm 2 ; P St ~ 1 … 2 g/mm 2 ; H ~ 6 … 8 kg/mm 2 Estimation of C D Radioluminesence of CsI crystal before (1) and after (2, 4) polishing. Curve 3 show difference 2 – 1. CsI Concentration of vacancies in LL is the same as an optimum C Na in CsI:Na 5 100CsI:Na Crystal with C Na = 8, cm –3 ~ ,5 8 m layer Polishing 1, ,5volumeIrradiation, D = 3200 Gy 1, volumeDeformation = 15% 1, volumeQuenching C D, см –3 S RL, %Treatment

6 6 E. Tchaikovsky model of dead layer formation predicts: Na + ions migrate to the surface; new phase of NaI is appeared on surface. DL Crystal E. Tchaikovsky model of DL formation in CsI:Na After DL formation the excitation of CsI:Na by soft X-rays (Curve 3) results in 310 nm luminescence (CsI pure) L. Dinca, et al, NIMA, A486 (2002) 141.

7 7 New model take into account the relaxation of LL: New model explains the kinetic of DL formation and predicts that decay of Na + solid solution results in broadening of the peak of fool absorption DLLL b nucleation Channel number

8 8 The change of fool energy absorption peak for -particles After LL relaxation -particles Crystal LL DL

9 9 Vacancy flow to the surface results in: (i) penetration of the OH – ions in LL; Confirmation of the OH – penetration to the LL; Degradation of light yield for -particle depends on humidity during aging.

10 Role of protective coatings 10 Application of protective coating results in the same degradation of the -yield as at H = 5% (curve 3 and 4). After application of protective coating the induced band at 270 nm do not revealed in absorption spectra (curve 2).

11 11 Wavelength [nm] Intensity [a.u.] Transparency [a.u.] In irradiated crystal there is a window of transparency at ~ 400 nm for converted light.

12 Radioluminescence of CsI 1 – initial; 2 – after polishing; difference Chemical Polishing of CsI Surface After Relaxation of Living Layer Permits to Excite the 310 nm Photoluminescence Photoluminescence of CsI 1 – after polishing; 2 – after LL relaxation at Н = 5 %; 3 – chemical polishing. 12

13 Tuning of CsI:Tl Scintillation Parameters The goal – mimimum R R G is a contribution of G to the R: R G = f (Z, k, n, r, p) Method – surface treatment to control the G(z) by change n, r, p Light yield: L = G (Z, t RC ) Energy resolution: R I 2 = R n 2 + R G 2 An example of the tuning of light yield uniformity 13

14 Instability of CsI surface optical properties 30 μm 14 21% of ready module needs an additional tuning after transportation ( u > 6%) independently of vendor Evolution of Scratch to the link of scalesDeep Scratch

15 Tuning of CsI:Tl crystals by WLS application Light output distribution along Z axis of CsI:Tl crystal. 1 – initial; 2 – wls coating КО-08 + sfPOdmaP; 3 – combination of different tuning. L 1 = 37,73% u 1 = 9,6 % L 2 = 39,45% u 2 = 4,2 % L 3 = 39,21% u 3 = 0,61 % 15

16 Conclusions Instability of CsI characteristic caused by surface effects: (i) relaxation of vacancy subsystem, and (ii) evolution of dislocation subsystem; 2. Protective coating on the surface of CsI scintillator permits to avoid the instability of CsI crystal characteristics at Natural and Radiation Aging

17 Спектры РЛ кристалла CsI:Tl (0,15 % Tl): 1 – исходного; 2 – с конвертором; 3 – поглощение пленки МФ (1-(1-нафтил)-3-(4-фторсуфонил- фенил)-5-фенил-2-пиразолин). 1 = 395; 2 = 550 нм; = 0,55. ССЭ на поверхности кристаллов CsI:Tl Спектры РЛ кристалла CsI:Tl (0,04 % Tl): 1 – исходного; 2 – с конвертором; 3 – поглощение пленки КО (4-сульфофторидофенил)-5-(4- диметиламинофенил)-1,3-оксазол. 1 = 400; 2 = 513 нм; = 0,56. 34

18 СПЕКТРОСМЕЩАЮЩИЕ ЗАЩИТНЫЕ ПОКРЫТИЯ ДЛЯ СЦИНТИЛЛЯЦИОННЫХ МОДУЛЕЙ CsI Конвертирование люминесценции с λ 1 = 310 нм в область λ 2 = 420 нм Состав конвертора: кремнийорганический лак КО-08 и две ЛД ( TB-PBD + Coum.1) TB-PBD 2-(4-третбутилфенил)-5- (4- бифенилоксадиазол)-1,3,4; Coum.1 7-диэтилоамино-4-метилкумарин Спектр РЛ кристалла CsI без (1) и с конвертором (2). Прозрачность покрытия (3). 28