A comparative study of promising filter materials for neutron imaging facilities

The effect of sapphire and bismuth single-crystal filters and their combinations on the quality of neutron radiographic images and neutron tomography data has been studied. The parameters of the contrast of the neutron image were analyzed depending on the monocrystalline filters. Neutron transmission spectra were obtained for sapphire and bismuth single crystals. Additionally, the effect of filters on the overall intensity of the thermal neutron beam and the background of gamma-rays was investigated. Based on the obtained data, we assume that a single-crystal sapphire filter can be most effectively used for radiographic and tomographic installations using thermal neutrons.

Измерение существенно нестационарных тепловых потоков градиентным датчиком на основе висмута

In this work we performed calibration of the gradient heat flux sensor made of bismuth single crystal. The value of the volt-watt sensitivity of the sensor is found and a data processing method based on the one-dimensional heat equation for a thin plate is presented. An experimental study of the heat flux on the frontal surface of the cylinder after a laser discharge was carried out. The data obtained as a result of the experiment were processed by the proposed method.

Эффекты Холла и Зеебека в тонких пленках висмута на подложке из слюды в диапазоне температур 77-300 K

The effects of film thickness and block size on the Hall and Seebeck effects in bismuth films on mica substrates are analyzed using experimental data. A preferential decrease in the electron contribution with a decrease in the film thickness and a preferential decrease in the hole contribution with a decrease in the block size are established. The Hall and Seebeck coefficients are calculated using the classical size effect with regard to carrier scattering at block boundaries and anisotropy of the properties of carriers. In the calculation, the electron and hole mobility components and their concentration in a bismuth single crystal are used and the crystallographic orientation of the film crystal are taken into account. The results of the calculation are in good agreement with the experimental data. It is concluded that the value and sign of the Hall and Seebeck coefficients in bismuth films are determined by the competition of the classical size effect and scattering at block boundaries.

Метод расчета нестационарного теплового потока по сигналу датчика на основе анизотропных термоэлементов из монокристалла висмута

We propose a method for calculating nonstationary heat fluxes using the electric-response signal of a sensor based on anisotropic bismuth single-crystal thermoelements. Using this method, it is possible to approximately calculate the heat flux during a period of time from ∼1 μs to the attainment of a stationary thermal regime. Tests showed that the monitoring of short-term ( t ∼ 1–10 ms) heat fluxes by bismuth-crystal-based sensors with a crystal length to thickness ratio of above 25 ensures a calculation error not exceeding several percent.