Miniband-related 1.4–1.8 μm luminescence of Ge/Si quantum dot superlattices

The luminescence properties of highly strained, Sb-doped Ge/Si multi-layer heterostructures with incorporated Ge quantum dots (QDs) are studied. Calculations of the electronic band structure and luminescence measurements prove the existence of an electron miniband within the columns of the QDs. Miniband formation results in a conversion of the indirect to a quasi-direct excitons takes place. The optical transitions between electron states within the miniband and hole states within QDs are responsible for an intense luminescence in the 1.4–1.8 µm range, which is maintained up to room temperature. At 300 K, a light emitting diode based on such Ge/Si QD superlattices demonstrates an external quantum efficiency of 0.04% at a wavelength of 1.55 µm

Photometry of ionizing radiations

Possibility to develop telemetry system for remote control of radiation environment in the preset points in space was examined and practically implemented. The system is based on the capability of certain media to emit visible-light photons under ionizing radiation. Dedicated high-aperture low-noise detector of photons operated within visual wavelength range allowing selective registration of light from the preset point is space was developed. Photon detector was developed on the basis of large-size paraboloid mirror and photomultiplier tube with cooled photocathode. Studies of luminosity of air, quartz glass, plexiglass and water under irradiation with alpha particles, beta particles and gamma quanta were performed using the developed equipment. It was demonstrated that the developed installation is capable to ensure remote detection of ionizing radiation with comparatively low dose rates. The best sensitivity of the installation during operation using air as the passive radiator was achieved under irradiation with alpha and beta particles. It is recommended to use radiators made of quartz glass and plexiglass for registration of gamma radiation. The main advantages of the system are the absence of cable communication lines between sensors and the light detection device, simplicity and reliability of the sensor, its high radiation resistance, expediency of the implemented control and possibility to simultaneously control several points inside the controlled premises. The developed installation can be useful for evaluation of radiation situation at facilities utilizing nuclear technologies both in normal operation conditions and during emergency situations accompanied with leakages of radioactive substances

Spectra of leakage neutrons from a Pb–Li spherical shell with central 252Cf and 14 MeV neutron sources and verification of evaluated neutron data

The spectra of leakage neutrons from a Pb83Li17 spherical shell with a 252Cf neutron source at its center have been measured by the time-of-flight method in a neutron energy range of 200 keV to 10 MeV. The outer radius of the spherical shell was 200 mm, and the inner radius was 60 mm. Measurements were performed with the use of a dedicated fast ionization chamber which simultaneously supplied stop pulses for the time-of-flight technique and recorded the total number of 252Cf decays for the experiment time. From the outer surface of the shell, the leakage neutrons were detected by a scintillation counter based on a paraterphenyl crystal with a diameter of 5 cm and a height of 5 cm and a FEU-143 photomultiplier tube. Earlier, spectra of leakage neutrons from the same spherical shell were measured with a 14 MeV neutron source using the same time-of-flight technique [1]. The results of the both measurements have been compared with the MCNP-4 Monte-Carlo code calculations with the ENDF/B-VII.1 and BROND-3 neutron data libraries

Benchmarking of thorium-232 evaluations against spherical transmission and (n,xn) reaction experimental data

The neutron leakage spectra from a thorium sphere of 26 cm outer and 6 cm inner diameters with a central T-D and 252Cf neutron sources measured at the Institute of Physics and Power Engineering as well as available in the literature measured differential cross sections for Th(n,xn) reaction at 14 MeV were used for benchmarking of the evaluated cross sections from ENDF (versions B-VII.0 and B-VI.8), JEFF-3.1 and Maslov'07 libraries. It was finally concluded that while it is difficult to prefer any of these libraries relying on spherical benchmarks validation results, Th(n,xn) differential cross sections are certainly better reproduced by ENDF/B-VII