Light transmission in a finely divided scintillator

The propagation of scintillation light is considered for a granular detector bounded by surfaces differing in reflectivity. The optimal parameters of the detector are considered; a comparison is made with experiment.     

The infrared absorption spectrum and the inversion degree of manganese ferrite

Infrared spectra of MnFe₂O₄ with inversion degrees of 0.05 and 0.2 are reported. It can be concluded that the absorption observed at 335 cm^?1 has to be the third fundamental IR active mode.     

Raman-scattering results on transformations in finely divided titanium dioxide

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 50, No. 6, pp. 937–945, June, 1989.     

Study of thermal diffusion in gases using infrared absorption spectra

The dependence of the integral intensity of the absorption bands due to the stretching vibrations of the NH groups of phthalimide and diphenylamine vapor on helium and nitrogen concentration has been used to study thermal diffusion in binary vapor-gas mixtures. A decrease or increase in absorption is observed, depending on the magnitude of the temperature gradient in the phthalimide-nitrogen mixture; this is related to a change in the sign of thermal diffusion. In the absence of a temperature gradient, added gases have no influence on the vibrational absorption bands of polyatomic molecules.     

The oxygen isotope effect on the infrared photo-induced absorption spectra of La2CuO4

The infrared photo-induced spectra of the isotope-substituted stoichiometric La₂CuO₄ samples were studied at T=20 K. Measured spectra were analyzed within the small polaron hopping theory. A small, but detectable shift of the effective phonon frequency on the substitution ¹⁶O to ¹⁸O is found for the high-energy surface carrier associated band (~4000 cm^-1) and has a value of α_O = 0.3 ±0.2. The low-energy band (~1500 cm^-1) originating from the bulk carriers doesn't show any difference within experimental error which is fully in agreement with theory predictions. The isotope shifts of the optically active oxygen-related phonon modes are described well by the harmonic approximation.     

Deflagration-to-detonation transition in mixtures of finely divided ammonium perchlorate with submicron aluminum powder

Deflagration-to-detonation transition in binary mixtures of fine ammonium perchlorate (20-μm grains) with submicron ALEX-L aluminum powder (0.2-μm particles) is studied using high-speed photography and pressure recording with quartz crystal sensors. The test mixtures were loaded in thin-walled quartz tubes of inner diameter 10 mm. The charges had a porosity of ~50%. It has been shown that, even under very mild conditions (low-strength shell and a weak source of initiation), the deflagration mode of mixture combustion easily transforms into the detonation mode. The shortest length of the region of transition from deflagration to normal detonation (not more than 30 mm) was observed for a lean mixture, with an aluminum content of ~5%. The mechanism of transition to detonation involves the stage of convective combustion, resulting in the formation of a brightly luminescent crescent-shaped area behind the primary flame front, which, in turn, generates a forward (in the direction of propagation) and a backward wave. The forward wave gives rise to low-speed detonation, which later transforms into normal detonation. The pressure profile within the region of low speed detonation is measured. A comparison with similar experiments in which ALEX-L alu- minum powder was replaced by ASD-4 aluminum (4 μm particles) shows that ALEX-L sensitizes the mixture, resulting in a dramatic reduction of the length of the transition region, making it possible to produce normal detonation in low-strength shells.     

The infrared absorption spectra and structure of some simpler alkoxides of lithium,sodium and potassium

The infrared absorption spectra of the crystalline methoxides of lithium, sodium and potassium and their deuterated derivatives, as well as the ethoxides of lithium and sodium, have been measured in the 2–25m region and interpreted. It has been shown that the successive displacement of the C-H (C-D) stretching frequencies to the longwave region, on passing from methanol to the methoxides of lithium, sodium and potassium, is determined by the differences in the nature of the O-H, O-Li, O-Na, and O-K bonds. The stretching frequency displacement effect and the structure of the compounds are discussed.In conclusion, we thank A. A. Trushanov for help in conducting the experiments.