Proton Induced Defect Formation in Quartz Glasses
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R.R.GULAMOVA, E.M.GASANOV and R.ALIMOV Institute of Nuclear Physics of Uzbekian AS p.Ulugbek, 702132 Tashkent, Uzbekistan (gasanov @pc202.suninp.tashkent.su) ABSTRACT The contributions of ionization energy losses and elastic collisions to radiation induced defect formation along the proton track were considered in quartz glasses irradiated by protons with different energies. It is shown that on a larger part of the proton track the color and luminescence center formation by means of recharging of the native defects is due to the ionization energy losses. Generation of structural defects like displaced atoms and their vacancies by elastic collisions with protons and recoil atoms dominates for proton energies < 5 MeV. At proton energies >10 MeV the color and luminescence center formation due to ionization energy losses prevails, and generation of the alumina-alkaline centers, causing an increase of the optical absorption at 550 nm and the thermoluminescence peak at 360 C and a band at 460 nm, occurs. At the proton energies Ep d when t = 2 mm (Table 1). The TL intensity of these p-exposed KI and KV glasses wit• t = 2 mm is also less than the TL intensity of the g-exposed samples (Fig. 1). The dependencies of dp at 550 nm on proton fluence and energy for KI glasses are illustrated in Fig. 3. As shown from Fig. 3, the values of dp decrease as the proton energy reduces from 18 MeV to 10 MeV.
The formation of intensive E'-centers upon proton irradiation of samples with t > L was
confirmed by results of thermal annealing of p-exposed samples illustrated also in Table 1. The p-exposed KV glasses were annealed at temperatures Ta = 450 and 900 C and re irradiated by the same doses of g-radiation. As shown from Table 1 for samples with t = 2 mm, dp > d'g > d" 9 . Evidently the heating of exposed samples up to 450 C does not fully anneal the proton generated defects, and, after g-irradiation, color centers are also created on these defects. As a result the values of dp and d'g are close to each other. The heating at 900 C fully anneals the radiation generated defects. In this case only g-radiation induced absorption is observed and dp > d"g = dg.
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A 6s8Otied do-fe (6y) Fig. 3. The optical densities dp at 550 nm vs the absorbed dose and proton fluence of KI quartz glasses with t = 2 mm exposed to protons with Ep = 10 MeV (1), 14 MeV (2) and 18 MeV (3).
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The observed dependencies may be explained with the mechanisms of interaction of protons with quartz glasses. As protons pass through quartz glasses, ionization energy losses dominate for Ep > 5 MeV. The formation of new structural defects at Ep > 5 MeV is not probable. As found for g-exposed quartz glasses, oxygen atom displacement by elastic collision with secondary electron is possible at the secondary electron energy E > 200 keV and when the oxygen threshold energy is equal to 16.5 eV or more [3,4]. The non bridging oxygen atom displacement occurs at the energies of secondary electrons
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