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

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 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 ;

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.

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

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.

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

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

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

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

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

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

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

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