Low-temperature photoluminescence in germanium irradiated by fast neutrons

This study was carried out to investigate low-temperature (T=4.2 K) photoluminescence caused by interdopant recombination transitions in n-germanium irradiated by fast (epicadmium) reactor neutrons and subjected to “complete” annealing (+450°C, 24 h). It is shown that lines of interdopant radiative recombination observed in initial and in irradiated and annealed specimens are caused by both initial impurities and (mainly) dopants (As and Ga) implanted by transmutation as well as by defect sets stable at long-time high-temperature annealing that do not contain fine dopants. Belarusian State University, 4, F. Skorina Ave., Minsk, 220050, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 4, pp. 479–482, July–August, 1997.     

IR spectra of fused silica irradiated by fast neutrons

IR spectroscopy has been used to study the process of structural damage and changes in some characteristics of fused silica irradiated by fast neutrons over a very broad fluence range (10¹⁷–10²¹ cm⁻²). Features of the change in spectral characteristics of the bending and stretching vibrations of the bridge bonds have been identified, and also a comparative analysis has been carried out with radiation-induced changes in a series of optical spectra in the UV and visible regions, and structural parameters and other characteristics of wafers irradiated by different fluences. A correspondence has been established between the features of the radiation-induced changes in the optical, luminescence, and structural properties, and extremal points have been observed on the dose dependences. Based on the results obtained, a mechanism of radiation-induced rearrangement of the silica structure is suggested. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 4, pp. 494–497, July–August, 2006.     

Electrophysical properties of carbon nanocomposites based on nanodiamonds irradiated with fast neutrons

The electrophysical properties of nanoporous carbon composites consisting of a nanometer-sized pyrolytic carbon matrix and nanodiamonds have been analyzed. It has been shown that the power-law dependence of the electrical resistivity on the thickness of the pyrolytic carbon layer D on a log-log scale has an inflection for D = 1 Å. It has been found that the temperature dependence of the electrical resistivity of the nanocomposite is described by an exponential function with an exponent of 1/4 for both unirradiated samples and samples irradiated with fast neutrons. This is characteristic of variable-range hopping conductivity in the case of strong localization in systems with semiconductor conductivity in the presence of a local disorder. With an increase in the neutron fluence, the electrical resistivity of the studied material changes very significantly (by several hundred percent) and nonmonotonically. This result is associated with the transformation of the structure of the graphite-like matrix and with possible graphite-diamond phase transitions.     

Amorphization of solids by fast neutrons

The diffraction patterns of amorphous solids prepared in the traditional way and by fast neutron bombardment are systematized. It is found that the diffraction patterns of these two classes of materials are different. In the case of a single crystal of titanium nickelide we have demonstrated here for the first time that these radiation-modified solids belong to the class of amorphous materials of distortion type. Fiz. Tverd. Tela (St. Petersburg) 40, 1584–1588 (September 1998)     

Transmutation doping of GaAs by thermal neutrons

The electrical properties of GaAs have been modified by transmutation of about 1 × 10¹⁸ As atoms per cm³ to Se and 0.7 × 10¹⁸ Ga atoms per cm³ to Ge in a flux of thermal neutrons, followed by annealing at temperatures from 625 to 900°C. Enhancement of carrier concentration was not observed in n⁺ samples, although p and n^? material showed changes in carrier concentration of the expected magnitude.     

Low temperature sound velocity at 9.3 GHz in quartz crystals irradiated with fast neutrons

Low temperature measurements of the variation of the velocity of sound in quartz crystals after exposure to various neutron doses are reported. The data, analysed in terms of the two-level tunneling model, show that the spectral density of tunneling systems as a function of neutron dose behaves different than the earlier reported density of radiation-induced clusters. To fit the maximum in Δv/v₀ at 7.5 K we used, like in a-SiO₂, a spectral density of tunneling states increasing with energy.     

Radio-frequency absorption study of the parameters of high-T c materials irradiated with fast reactor neutrons

The magnetic properties of YBa₂Cu₃O_7−x ceramics of various densities and Bi₂Sr₂CaCu₂O₈ quasicrystals irradiated with neutrons at fluences of 10¹⁶–10¹⁹ cm⁻² are investigated by a radio-frequency method (in the frequency range f=100–150 MHz). The electromagnetic absorption is used to estimate the parameters of a Josephson medium: the lower critical field, the critical current density, the grain size and intergranular distances, and the penetration depth of the magnetic field in the sample. The hysteresis of electromagnetic absorption in the indicated superconductors is investigated; the hysteresis effect can be used to obtain data on flux pinning processes and flux creep dynamics. It is shown that an increase in the critical current density is observed as a result of the injection of radiation-induced pinning centers. Fiz. Tverd. Tela (St. Petersburg) 39, 28–34 (January 1997)     

Non-steady-state photoelectromotive force in SiC crystals irradiated by reactor neutrons

The effect of the non-steady-state photoelectromotive force in 6H-SiC crystals irradiated by reactor neutrons has been investigated experimentally. The dependences of the signal amplitude on the phase modulation frequency, spatial frequency, light intensity, and amplitude of an external alternating-current (ac) electric field have been analyzed. The unusual frequency dependence of the signal has been explained in terms of the two-level semiconductor model taking into account shallow traps. The photoelectric parameters of the crystals have been determined for the light wavelength λ = 532 nm.     

ESR of pyrolytic graphite irradiated by neutrons at low temperature

Pyrolytic graphite irradiated by neutrons at a low temperature was studied by esr. The presence of localized spin centers was confirmed from the esr intensity ratio between room temperature and liquid nitrogen temperature. The concentration ratios of localized spin centers to conduction carriers were obtained from g-values for various irradiation doses. The dose dependence of g-values and widths was explained by the rapid exchange interaction between the two spin systems, i.e. localized spin centers and conduction carriers. An increase of the width was observed around 160 K by pulse annealing experiments. The mechanism of the broadening was discussed and the spin-flip cross section was estimated in order of magnitude. The annealing behavior of the line-width above 300 K was explained as due to the annihilation of localized spin centers.     

Electrophysical properties and annealing of defects in nuclear transmutation-doped GaAs irradiated by H+ ions

A study has been made of the electrophysical characteristics of nuclear-transmutation-doped GaAs (NTDG) and GaAs doped with metallurgical impurities Sn, Te, Ge, and In, after irradiation by H⁺ ions at fluxes of up to 1.5·10¹⁶ cm^–2. It is shown that the changes in the GaAs produced by irradiation do not depend on the method used to dope the material and can be described on the basis of the known spectrum of E and H traps in GaAs. Crystals of GaAs annealed after irradiation display deep (P1–P3) traps, which are responsible for the high-temperature proton insulation GaAs.V. D. Kuznetsov Siberian Physicotechnical Institute at the State University, Tomsk. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 61–65, October, 1992.     

Raman scattering by two-phonons and fractons in irradiated GaAs

The second-order transverse acoustic mode and amorphous Raman modes, originating from a continuous random network and medium range ordering (MRO), in high energy light ion (HELI) irradiated GaAs are investigated. The change in the phonon density of states of the transverse acoustic mode phonon distinguishes the effect of HELI irradiation on highly resistive undoped and chromium-doped GaAs. The boson mode, originating from the MRO of the system, has been identified and a model based on phonon-fracton scattering has been used for the explanation of this “boson mode”. The spectral dimension, correlation length and the scaling factor, with which the elastic constant varies with length in MRO regions in GaAs, are estimated.     

Angular-distribution neutron-emission spectra of niobium following bombardment by fast neutrons

Neutron-emission spectra at ten angles between 20 and 160 degrees and incident neutron energies of 5.9, 7.1 and 8.4 MeV were measured relative to the neutron field emitted after spontaneous fission of ²⁵²Cf. The angular distribution of inelastically scattered neutrons appears to be essentially isotropic where it can be separated from the dominant elastic scattering peak. Above an excitation energy of 4 MeV the spectra are well described by a Maxwellian temperature distribution.