卤化物钙钛矿射线探测器材料研究进展

卤化物钙钛矿由于具有高射线吸收系数、高载流子迁移率寿命乘积、可低温溶液法生长等特性,有望突破传统高纯锗和碲锌镉探测器在成本、芯片兼容性和大尺寸成像等方面的制约,成为新一代性能优异的室温射线探测材料。本文从卤化物钙钛矿材料的基本性质与射线探测原理出发,介绍了2015年以来卤化物钙钛矿射线探测材料与器件的发展历程;系统介绍了直接型射线探测器(强度、成像、能谱)及闪烁体探测器的最新研究成果;分析了材料特性与器件结构对射线探测器性能的影响机制,为今后更高效的卤化物钙钛矿射线探测器的开发提供参考。     

<Superscript>137</Superscript>Cs content and vertical migration in littoral soil of two lakes in Bryansk Oblast

The dynamics and present state of the radioactive contamination with ¹³⁷Cs of littoral soil of Lake Kozhanovskoe and Lake Svyatoe on the Besed’ River are presented. The parameters of the vertical migration of ¹³⁷Cs in soil-the rate of directional transfer with soil moisture, the diffusion coefficient, and the average velocity of vertical migration-are estimated by comparing the experimental and model distributions of ¹³⁷Cs content over soil depth. It is shown that at the present time the two 5-cm layer of soil can contain 20–90% ¹³⁷Cs depending on the type of soil and landscape. The average values of the diffusion coefficient, the rate of directional transfer, and the vertical migration velocity for 12-, 13-, and 20-year periods after the Chernobyl accident are 0.1–2.8 cm²/yr, 0.1–0.3 cm/yr, and 0.1–0.8 cm/yr, respectively. __________ Translated from Atomnaya énergiya, Vol. 102, No. 5, pp. 306–311, May, 2007.     

Coherent population trapping on <Superscript>87</Superscript>Rb atoms in small-size absorption cells with buffer gas

Coherent population trapping (CPT) on ⁸⁷Rb atoms in neon atmosphere has been studied in small-size glass absorption cells under conditions of pumping with narrow-band laser radiation at the D₂ line of the main doublet. Parameters of the absorption signal have been measured in 3-mm-diameter cells at buffer gas (Ne) pressures varied within 200–400 Torr, cell temperatures within 65–120°C, and pumping radiation power densities within 30–400 μW/cm². Optimum values of the buffer gas pressures, cell temperature, and pumping power are determined at which the short-term instability of the resonance line is at minimum. Orientational shifts of the CPT resonance signal in gas-filled cells and small-size cells with antirelaxation coating have been compared.     

Coaxial Alginate Hydrogels: From Self-Assembled 3D Cellular Constructs to Long-Term Storage

Alginate as a versatile naturally occurring biomaterial has found widespread use in the biomedical field due to its unique features such as biocompatibility and biodegradability. The ability of its semipermeable hydrogels to provide a favourable microenvironment for clinically relevant cells made alginate encapsulation a leading technology for immunoisolation, 3D culture, cryopreservation as well as cell and drug delivery. The aim of this work is the evaluation of structural properties and swelling behaviour of the core-shell capsules for the encapsulation of multipotent stromal cells (MSCs), their 3D culture and cryopreservation using slow freezing. The cells were encapsulated in core-shell capsules using coaxial electrospraying, cultured for 35 days and cryopreserved. Cell viability, metabolic activity and cell–cell interactions were analysed. Cryopreservation of MSCs-laden core-shell capsules was performed according to parameters pre-selected on cell-free capsules. The results suggest that core-shell capsules produced from the low viscosity high-G alginate are superior to high-M ones in terms of stability during in vitro culture, as well as to solid beads in terms of promoting formation of viable self-assembled cellular structures and maintenance of MSCs functionality on a long-term basis. The application of 0.3 M sucrose demonstrated a beneficial effect on the integrity of capsules and viability of formed 3D cell assemblies, as compared to 10% dimethyl sulfoxide (DMSO) alone. The proposed workflow from the preparation of core-shell capsules with self-assembled cellular structures to the cryopreservation appears to be a promising strategy for their off-the-shelf availability.     

A new recombination center in heavily doped GaAs: Zn grown by liquid-phase epitaxy

The photoluminescence properties of p-GaAs: Zn (100) layers grown by liquid-phase epitaxy from gallium and bismuth melts at various temperatures have been studied. It is shown that a novel radiative recombination center is formed in these layers. The concentration of the centers increases with the doping level in proportion to the concentration of free holes raised to the power 5.35±0.1. The exponent is independent of the growth melt (gallium or bismuth) and the growth temperature. It is found that the center is a neutral complex consisting of an antisite defect of gallium at an arsenic site and two arsenic vacancies. Fiz. Tekh. Poluprovodn. 32, 1184–1189 (October 1998)     

Test selection based on communicating nondeterministic finite-statemachines using a generalized Wp-method

Presents a method of generating test sequences for concurrent programs and communication protocols that are modeled as communicating nondeterministic finite-state machines (CNFSMs). A conformance relation, called trace-equivalence, is defined within this model, serving as a guide to test generation. A test generation method for a single nondeterministic finite-state machine (NFSM) is developed, which is an improved and generalized version of the Wp-method that generates test sequences only for deterministic finite-state machines. It is applicable to both nondeterministic and deterministic finite-state machines. When applied to deterministic finite-state machines, it yields usually smaller test suites with full fault coverage than the existing methods that also provide full fault coverage, provided that the number of states in implementation NFSMs are bounded by a known integer. For a system of CNFSMs, the test sequences are generated in the following manner: a system of CNFSMs is first reduced into a single NFSM by reachability analysis; then the test sequences are generated from the resulting NFSM using the generalized Wp-method