Results 1 - 10 of 8575
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[en] The electro-optic contributions to second-order Raman scattering and field-induced first-order scattering from alkali halides are calculated explicitly in terms of the ionic hyperpolarizability coefficients. The relevant local-field corrections are evaluated. Illustrative numerical results are presented
[en] It is generally assumed that after the readout of TLD chips, all the traps are almost completely emptied and the residual readout is negligible. However, when performing routine readings (short readout times and high heating rates with no annealing), the deep traps are not completely cleared, and therefore, an additional readout of the crystal will indicate a residual dose. The residual dose for a normal additional readout (without any special treatment to enhance the residual dose, like UV irradiation) is about 0.2% of the accumulated historical dose of the TLD chip and could affect the result of the following readouts, especially when estimating low level doses
[en] The influence of the maximum readout temperature on the LiF GR-200 dose response was studied. A fast heating rate (8oC.s-1) and a new method to set the maximum readout temperature were employed for this study. The new method determines on each measurement the maximum temperature with reference to the position of the main TL peak. This is achieved through the on-line analysis of the glow curve during heating. The good measurement reproducibility attained by using this method and a previously described computerised method for TL evaluation is also presented. (author)
[en] Accurate knowledge of energy absorption coefficients is needed to calculate the absorbed dose in any material. The photon kerma for LiF relative to air and soft tissue is computed using energy absorption coefficient values for Li, F, air, and tissue. Values of energy absorption coefficients for air are already available in J. H. Hubbell's (Photon Cross-Sections, Attenuation Coefficients and Energy Absorption Coefficients from 10 KeV to 100 GeV. National Standard Reference Data System-National Bureau of Standards Report No. 29, Washington, D. C., 1969) tables. Those for tissue are obtained by adding the weighted average of the energy absorption coefficients to the different elements constituting the tissue. For fluorine, they are computed from the values given by F. H. Attix and W. C. Roesche (Eds, Radiation Dosimetry, Vol. I, Fundamentals. Academic Press, New York/London, 1968) for CaF2 and Ca. The values for lithium have been computed taking into consideration the photoelectric effect, Compton process, and pair production. Corrections for radiative energy losses, fluorescence yields, screening of electrons, etc., are appropriately applied. The energy absorption coefficients due to photoeffect, Compton scattering, and pair production are added to get the total. The energy absorption cross-section data for photon energies from 0.01 to 10 MeV are tabulated for each interaction
[en] Highlights: • The collision efficiencies of vibrational relaxation of S2(a1Δg) by He are 10−3–10−2. • Vibrational relaxation rates of S2(a1Δg, υ) by He increase superlinearly with υ. • Relaxation of S2(a1Δg) + He system is much faster than that of + He system. • The V–T processes of S2(a), O2(X), NO(X), and CO(X) by He are correlated by the gap law. Vibrationally excited S2(a1Δg, υ = 1–10) was generated by the S(1D) + OCS reaction and detected with dispersed laser-induced fluorescence (LIF) via the f1Δu–a1Δg transition. The time profiles of the vibrational levels of interest were recorded at varying pressures of He. A kinetic analysis made by the integrated profiles method has given the rate coefficients for vibrational relaxation of S2(a1Δg, υ = 1–9) by collisions with He. The energy gap law nicely correlates the probabilities of vibrational energy transfer per collision from S2(a1Δg), , NO(X2Π), and CO(X1Σ+) to He.
[en] In this letter we report the observation of amplified spontaneous emission of the red light from LiF:F2 centers in active channel waveguides realized by electron-beam lithography in lithium fluoride crystals. Low pumping power densities have been used in quasi-continuous-wave regime at room temperature; the appreciable values of the gain coefficients, 4.67 cm-1 with an exciting power density of 0.31 W/cm2 at 458 nm, make this material a good candidate for the realization of active integrated optical devices. [copyright] 2001 American Institute of Physics
[en] The regeneration rate prediction model representing the regenerator performance in a liquid desiccant system was derived by statistically analyzing the empirical data collected from the real liquid desiccant unit operated under various conditions. In order to propose a simple empirical regenerator model with wide valid range, additional experimental data found in open literature were also considered in the model derivation. The lithium chloride (LiCl) solution was used as a working desiccant solution. Response surface methodology was used to identify operating parameters and their interactions affecting significantly on the regenerator performance in a liquid desiccant system. Consequently, a first-order linear regression equation was derived as a function of the major parameters and interactions, which returns the regeneration rate in various operating conditions. The reliability of the proposed model was confirmed via the analysis of variation (ANOVA). The proposed model agreed well with the experimental data and other existing models. - Highlights: • A model was developed for predicting the performance of a packed-bed regenerator. • The model was derived based on experimental data collected from the real operation and open literature. • The model is expected to have a wider operating range than an existing model.
[en] A microdosimetric, track interaction model for heavy charged particles has been developed which is capable of quantitatively predicting the experimentally observed supralinearity of the alpha particle TL dose response of peak 8 in LiF:Mg,Ti as well as the linear behaviour of the lower temperature glow peaks. The linear behaviour at low dose is due to lack of track interaction arising from the highly localised nature of the alpha particle dose deposition profile. Track dose overlap in the radiation absorption stage is shown to be incapable of increasing the TL efficiency at virtually all values of the nearest neighbour track axis separation distance. The alpha induced supralinearity of peak 8 can therefore be explained only via greatly increased charge carrier migration lengths in the glow curve heating stage which brings about significant nearest neighbour track interactions above approximately 108 alpha particles per cm2. The linear behaviour of the lower temperature peaks yields a charge carrier mean free path of approximately 250 A which implies that at low glow peak temperatures there is little inter-track migration of charge carriers in the luminescence recombination stage. (author)