Yu.M. Aleksandrov

Radiative transitions between anion and cation valence bands in CsBr and CsCl crystals

Abstract For CsBr and CsCl crystals excitation spectra of fast intrinsic luminescence due to radiative transitions between anion and cation valence bands were investigated under pulsed synchrotron radiation (10–30 eV) excitation.

Exciton and electron-hole mechanisms for electronic excitation multiplication in alkaline earth fluoride crystals

Abstract Electronic excitation multiplication processes in alkaline earth fluoride crystals were investigated and the methods for separating exciton and electron-hole multiplication mechanisms are discussed.

Investigations on the S-60 SR source of the Lebedev Physical Institute

Abstract Results of experiments on the luminescence of some crystals and glasses are presented. The materials investigated are promising scintillators for high energy physics experiments. The biological structure of some specimens was determined by measuring the time response of fluorescent probes or of natural fluorophosphors embedded in the examined structures. Capillary structures and results of calibrations of materials sensitive to soft X-ray radiation are also presented.

Intrinsic and impurity cross-luminescence in three-component barium-containing compounds

Abstract Time-resolved luminescence excitation spectra under synchrotron radiation (10–30 eV) excitation for the barium-containing compounds BaLn 2 F 8 (Ln = Y, Tm, Yb), (BaF 2 ) 1- x (NdF 3 ) x ( x = 0.005−0.3) and SrF 2 Ba 2+ (0.1–1%) were investigated. It was shown that BaY 2 F 8 crystals have fast cross-luminescence with an excitation threshold at hv = 19.3 eV and spectral characteristics similar to that of BaF 2 . By introducing in BaF 2 rare-earth elements with unfilled 4f-shells the long luminescence of self-trapped excitons is suppressed, but fast cross-luminescence is suppressed as well. The existence of impurity cross-luminescence in SrF 2 Ba (excitation threshold at about 18.5 eV) was confirmed. Investigations of impurity cross-luminescence give information about the band structure of crystals which do not have intrinsic cross-luminescence.

Multipole analysis of pion photoproduction on protons near P33 (1236) resonance

The results of an energy-independent multipole analysis of pion photoproduction on protons are presented for the region of the P33 resonance. The analysis includes the phenomenological fitting of the experimental data by the linear model. We have obtained the channel amplitudes of the γp→nπ+ process without using the Watson theorem and the isospin amplitudes of the γp→nπ+ and γp→pπ0 processes using the πN phase shifts. All the results are discussed and compared with the theoretical predictions. From the channel amplitudes obtained an attempt has been made to evaluate the phases of M1+(3).

POSITIVE PION PHOTOPRODUCTION FROM HYDROGEN AT LARGE ANGLES IN THE REGION OF THE FIRST RESONANCE.

Abstract The results of measurement of differential cross sections for the process γp → nπ+ are presented for γ-ray energies 260, 290, 320 MeV and pion angles 90°–180°.

Application of the pulsed synchrotron radiation for investigation of the fast crystalline scintillators

A new family of the fast crystalline scintillators, so‐called crossluminescence crystals, is proposed for using in high‐rate detectors of x‐ray synchrotron radiation. The results of the fast luminescence investigations in ionic crystals of different classes using the time‐resolved spectroscopy technique under excitation by pulsed synchrotron radiation (5–30 eV) are presented. The general characteristics of crossluminescence in binary and some ternary ionic crystals as well as luminescence properties of rare‐earth trifluorides are discussed.

Analysis of angular distributions for the process γp → nπ+ in the region of 230–350 MeV

Abstract The results of the phenomenological analysis of the positive photopion angular distributions are presented for the photon energies 230, 260, 290, 320 and 350 MeV. Along with the Moravcsik fit a new form of fitting is used.

Ambiguity of multipole analysis and new amplitudes of the γp → nπ+ process

Abstract A multipole analysis of the γ p → n π + process using new data on the angular distributions of the polarized photon asymmetry has been made. At present the difference between the phase of the resonance amplitude M 1+ 3 2 and the corresponding πN scattering phase shift is found to be −2.5° ± 1.1°. The problem of the ambiguous solutions of a system of equations with respect to the multipole amplitude has been discussed.

Specific features of poly(methyl methacrylate) irradiation

Abstract Spectral sensitivity of poly(methyl methacrylate) films to synchrotron radiation was investigated. In the wavelength region 24 to 44 A and at a development depth of 1 μm the polymer was found to exhibit enhanced sensitivity.