Formation of Defects by Radiation in KBr-Li and KBr-Na crystals K.S. Baktybekov , A.K. Dauletbekova L.N. Gumilyov Eurasian National University, 5 Munaitpassov str., 010008, Astana, the Republic of Kazakhstan, E-mail: mzdorovets@inbox.ru Abstract – The article regards influence of M A – impurity ( Li + and Na + ) on formation of defects by X-radiation in KBr-Li and KBr-Na crystals. The concentration of impurity, temperature of irradia- tion and dose were determined by the method of absorption spectroscopy. When interaction of mov- ing, non relaxed exсitons with the impurity is high (for KBr it is either pre-helium temperature or high-impurity concentration) we can see the pic- ture of suppression by impurity effect of defect of pre-impurity excitation on Frenkel defects in an anion lattice. The dependence of defect-creation for 5K on the concentration of impurity has a linear character. By using this fact the assessment of the exciton’s free path yields the 100 lattice constants. Besides we regard a model of tunnel overcharge of F-H A pair, basing on the F-centre model which supposed that the tunnelling electron is localized on the M A -ion and if there is an H-centre nearby, so the complex M 0 A Br - 2 is formed. In the ultimate result the complex turns into I A –centre. 1. Introduction. We observe the suppression of radiated defect- formation beginning with just a little concentration of impurity in case of X-irradiation of KBr crystals, con- taining M A – impurity (Li + or Na + ) for 5K. We dis- cover the same effect for 80K having larger concentra- tion of impurity that is in case when the interaction of exciton with the impurity is high so radiating decay of exciton from ion of impurity would take place without process of defect-formation [1,2,3]. The absorption spectrum of KBr-crystals with M A – impurity, having X-irradiated at 80K, and depending on level of the concentration of the impurity contain as defects of pure KBr (F, V, α) as impurity radiated defects of interstitial origin: H A -, I A -, V 4A - centres. Increasing concentration of Na + -impurity to 1 mol.% we see an effect of moving of radiated defects towards α -I A pair, we explain it as tunnel overcharge of F-H A J α -I A pairs [3]. The view of the absorption spectrum of KBr-Na 1mol.% X-radiated at 80K is simple, they contain ab- sorption bands of α−, F-, H A - and I A - centres, but there is no absorption of V-centres. 2. Experimental procedure. Monocrystals KBr- Li and KBr- Na were grown by Stokbarger’s method by means of recourse having cleaned from OH - . The amount of Na + -impurity we have defined by the method of spectrum analysis, and concentration Li + – by number of impurity radiated defects taking into accountant the saturation of the impurity defects. The results are based on value, as- sessed by a coefficient of distribution of Li + in KBr (0.02–0.03) [4]. The samples were radiated with URS -50 (55 kV, 20 mA, W). The absorption spectra were recorded by means of the Specord UV- VIS. 3. Results and discussion. We made a graphic of dependence of F- centre absorp- tion on number of impurity ions by means of analysis of absorption spectrum of KBr-LI crystals with differ- ent level of the impurity concentration, X-radiated at 5K (Fig. 1). Fig. 1. Dependence of the absorption in I- band at 5.2 eV and in K-band at 2.35 eV on Li + concentra- tion for KBr-Li : radiated during 225 minutes for 5 K (1 and 2) and for 80 K (1’ and 2’) Taking into accountant the line character of de- pendence of defect-formation on the impurity concen- tration we can show the total probability of annihila- tion of exiton by the formula: 1=P A + P R , P A – probability of exciton’s autolocalization, P R – probabil- ity of radiated decay of exciton. Less possible canals of annihilation aren’t regarded, then: 1 – P A = P R , P R = R σ , where R – the exciton’s free path, σ – a section of capture, n-number of impurity ions in 1cm 3 , if σ = πd 2 /4, d – cation-anion distance, for Li-Br it is 3.17·10 -10 m [5] for Rσ we have the value 5·10 -21 cm 3 and for R is cm –3 42 ___________________________________________________________________________________________ Elementary processes