Results 1 - 10 of 97
Results 1 - 10 of 97. Search took: 0.026 seconds
|Sort by: date | relevance|
[en] Study of photoelectric features of the irradiated samples of p-Ga S showed that the defect formation process leads to a strong change in concentrations of local levels, including r-centers of photosensitivity within gamma-irradiation. For the purpose of determination of the mechanism of recombination parameters of the recombination centers, the scheme of electronic transitions in Ga S crystals, we used a set of stationary and kinetic methods. Study of photoelectric features of the irradiated samples of p-Ga S showed that the defect formation process leads to a strong change in concentrations of local levels, including r-centers of photosensitivity within gamma-irradiation.
[en] The feasibility of utilizing the pre-dosed OSL signal in the estimation of the equivalent dose has been investigated. The results based on (i) the behavior of growth curve, (ii) dose recovery tests and (iii) non-bleachability of reservoir centres, R-centres, suggests that (i) the pre-dosed OSL does not seem to work satisfactorily in dose estimation unlike the pre-dosed 110 deg. C TL emission and (ii) it may not be applicable in case of bleached specimen.
[en] The evolution of novel procedures for the evaluation of equivalent dose using the optically stimulated luminescence (OSL) signal of quartz became necessary to address (i) the sensitization experienced by the signal during the pre-heat treatment and (ii) the in situ sensitization occurring in nature. The pre-dose phenomena of the OSL and 110 deg. C TL pre-dose emissions have been reported to be similar. In light of this observation, an attempt has been made in this paper to visualize the role of R-centres in the sensitization process of the OSL emission. The results, based on the experimental observations and kinetics considerations of R-centres, confirm that the R-centres participate in the sensitization process of this signal.
[en] The paper presents a numerical model of pre-dose sensitisation in quartz. In particular, the thermal activation characteristics (TAC), isothermal sensitisation and the form of TAC for high values of pre-dose are considered. Relevant experimental results are shown and a suitable numerical model is derived. The model, based on Zimmerman's model consists of four hole centres (two shallow R-centres, one deeper R-centre and one L-centre), two electron traps responsible for the 110 deg. C peak and 320 deg. C peaks, respectively, and one reservoir electron trap. The form of TAC, isothermal sensitisation and the form of TAC for high doses are modelled. The modelled results are very similar to the empirical ones indicating that the suggested model might be successfully employed to investigate phenomena connected with sensitivity changes in quartz
[en] Two new low-symmetry electron spin resonance (ESR) centres, with S = 1 and referred to as R14 and R15, have been observed in electron- and neutron-irradiated type Ia and type IIa diamonds. R15 was observed only after the diamond was given an ionization pulse. R14 is produced with similar concentration and anneals out in the same temperature range as the ESR centre R3. Possible models for the R14 and R3 centres are discussed. (author)
[en] The understanding of all luminescence processes occurring in quartz is of paramount importance in the further development of robust absorbed dose estimation techniques (for the purpose of dating and retrospective dosimetry). The findings presented in this thesis, aid future improvements of absorbed dose estimation techniques using quartz by presenting investigations in the following areas: 1) interpretation of measurement results, 2) numerical modelling of luminescence in quartz, 3) phenomena needing inclusion in future physical models of luminescence. In the first part, the variability of properties of single quartz grains is examined. Through empirical and theoretical considerations, investigations are made of various problems of measurements of luminescence using multi-grain aliquots, and specifically areas where the heterogeneity of the sample at the inter-grain level may be misinterpreted at the multi-grain-aliquot level. The results obtained suggest that the heterogeneity of samples is often overlooked, and that such differences can have a profound influence on the interpretation of measurement results. Discussed are the shape of TL glow curves, OSL decay curves, dose response curves (including consequences for using certain signals as proxies for others), normalisation procedures and DE estimation techniques. Further, a numerical model of luminescence is proposed, which includes multiple R-centres and is used to describe the pre-dose sensitisation in quartz. The numerical model exhibits a broad-scale behaviour observed experimentally in a sample of annealed quartz. The shapes of TAC for lower (20 Gy) and higher doses (1 kGy) and the evolution with temperature of the isothermal sensitisation curves are qualitatively matched for the empirical and numerical systems. In the third area, a preliminary investigation of the properties of the '110 deg. C peak' in the 550 nm emission band, in annealed quartz is presented. These properties are in sharp contrast with the properties of the '110 deg. C peak' in the 360 nm emission band (e.g. significantly different saturation characteristic and thermal sensitisation characteristic). These differences in behaviour are difficult to incorporate into the band model of luminescence and remain unexplained. (author)
[en] The transformation of F to R centres in KCl has been investigated by means of optical absorption and positron annihilation measurements. The intensity of the long-lived component (approximately equal to 1 ns) in the life-time spectra, which is due to annihilation in F centres, decreases with increasing R centre concentration. A simple model is proposed to explain the experimental data, from which it is indicated that annihilation in R centres takes place with a lifetime of only approximately 200 ps. The oscillator strength of the R1 band is determined to be about 0.3. (author)
[en] In this work the colour centers of magnesium fluorides crystals induced by Co60 gamma-radiation with the dose 109 rad and photoluminescence(PhL) excited on these centers are investigated. After gamma-irradiation in PhL spectra the bands with maxima 420, 460, 530 and 620 which are excited correspondingly on the bands with maxima 370, 330, 410 and 470 are displayed. Taking into account data on absorption spectra it was assumed that these colour centers are of M and R ones