Study of Light Neutron-Rich Nuclei Using a Multilayer Semiconductor Setup

The characteristics of two modifications of the semiconductor (s.c.d.) setup consisting of telescopes on the basis of silicon detectors are presented. These settings allow performing a precision measurement of energy in a large dynamic range (from a few to hundreds of MeV) and particle identification in a wide range of masses. The issues of measurement of the characteristics of s.c.d. telescopes and their impact on the quality of the obtained experimental data are considered. Considerable attention is paid to the use of created semiconductor devices for the search for and spectroscopy of light exotic nuclei on the accelerators of PNPI (Gatchina) and LANL (Los Alamos).     

The QE numerical simulation of PEAsemiconductor photocathode

Several kinds of models have already been proposed to explain the photoemission process. The exact photoemission theory of the semiconductor photocathode was not well established after decades of research. In this paper an integral equation of quantum efficiency (QE) is constructed to describe the photoemission of positive electron affinity (PEA) of the semiconductor photocathode based on the three-step photoemission model. Various factors (e.g., forbidden band gap, electron affinity, photon energy, incident angle, degree of polarization, refractive index, extinction coefficient, initial and final electron energy, relaxation time, external electric field and so on) have an impact on the QE of the PEA semiconductor photocathode, which are entirely expressed in the QE equation. In addition, a simulation code is also programmed to calculate the QE of the K₂CsSb photocathode theoretically at 532 nm wavelength. By and large, the result is in line with the expected experimental value. The reasons leading to the distinction between the experimental and theoretical QE are discussed.     

Precision Measurements of High-Energy Cosmic Gamma-Ray Emission with the GAMMA-400 Gamma-Ray Telescope

The GAMMA-400 γ-ray telescope installed at the Russian space observatory is intended for precision measurements in the energy range of 20 MeV–1000 GeV of γ-ray emission (with the angular and energy resolutions several times better than that of current γ-ray telescopes) from discrete sources; measurement of the energy spectra of Galactic and extragalactic diffuse γ-ray emission; studies of γ-ray emission from the active Sun; and measurements of fluxes of γ-ray emission and electron–positron cosmicray component, which are probably associated with the annihilation or decay of dark-matter particles.     

Measurements of charge transfer efficiency in a proton-irradiated swept charge device

Charged Coupled Devices (CCDs) have been successfully used in several low energy X-ray astronomical satellites over the past two decades. Their high energy resolution and high spatial resolution make them a perfect tool for low energy astronomy, such as observing the formation of galaxy clusters and the environment around black holes. The Low Energy X-ray Telescope (LE) group is developing a Swept Charge Device (SCD) for the Hard X-ray Modulation Telescope (HXMT) satellite. A SCD is a special low energy X-ray CCD, which can be read out a thousand times faster than traditional CCDs, simultaneously keeping excellent energy resolution. A test method for measuring the charge transfer efficiency (CTE) of a prototype SCD has been set up. Studies of the charge transfer inefficiency (CTI) with a proton-irradiated SCD have been performed at a range of operating temperatures. The SCD is irradiated by 3×10⁸cm^-2 10 MeV protons.     

A perspective view to hard-X-ray astronomy

Summary The present observational and instrumental status of hard-X-ray astronomy ((10÷200) keV) is discussed. The relevance of observations in this energy range is stressed and a few examples of unsolved observational problems in galactic and in extragalactic astronomy are discussed. In these examples we focus on the possibility to solve the problems with observations using detectors of the current generation. In this framework, the performances of the most sensitive hard-X-ray detectors are discussed with particular emphasis on the control of systematic errors. Quite simple but unavoidable considerations on limits of the present generation of hard-X-ray detectors (supported by results of simple simulations) lead to the conclusion that a decisive breakthrough can be achieved only using optics with a sufficiently good concentration power. In particular we discuss the feasibility of hard-X-ray telescopes (with a concentration power ≫1), using either grazing incidence or Bragg diffraction. The use of concentrators in this energy band can also make feasible polarimetric measures of a substantial sample of X-ray sources, up to now severely limited by the very low detection efficiency of the devices used in polarimetry. Paper presented at the V Cosmic Physics National Conference, S. Miniato, November 27–30, 1990.     

Active galactic nuclei at gamma-ray energies

Active Galactic Nuclei can be copious extragalactic emitters of MeV–GeV–TeV γ rays, a phenomenon linked to the presence of relativistic jets powered by a super-massive black hole in the center of the host galaxy. Most of γ-ray emitting active galactic nuclei, with more than 1500 known at GeV energies, and more than 60 at TeV energies, are called “blazars”. The standard blazar paradigm features a jet of relativistic magnetized plasma ejected from the neighborhood of a spinning and accreting super-massive black hole, close to the observer direction. Two classes of blazars are distinguished from observations: the flat-spectrum radio-quasar class (FSRQ) is characterized by strong external radiation fields, emission of broad optical lines, and dust tori. The BL Lac class (from the name of one of its members, BL Lacertae) corresponds to weaker advection-dominated flows with γ-ray spectra dominated by the inverse Compton effect on synchrotron photons. This paradigm has been very successful for modeling the broadband spectral energy distributions of blazars. However, many fundamental issues remain, including the role of hadronic processes and the rapid variability of a few FSRQs and several BL Lac objects whose synchrotron spectrum peaks at UV or X-ray frequencies. A class of γ-ray-emitting radio galaxies, which are thought to be the misaligned counterparts of blazars, has emerged from the results of the Fermi-Large Area Telescope and of ground-based Cherenkov telescopes. Soft γ-ray emission has been detected from a few nearby Seyfert galaxies, though it is not clear whether those γ rays originate from the nucleus. Blazars and their misaligned counterparts make up most of the ≳100 MeV extragalactic γ-ray background (EGB), and are suspected of being the sources of ultra-high energy cosmic rays. The future “Cherenkov Telescope Array”, in synergy with the Fermi-Large Area Telescope and a wide range of telescopes in space and on the ground, will write the next chapter of blazar physics.     

High-energy neutron spectrometry

We review progress made in the last quarter of a century in the field of neutron spectrometry over a wide energy range from ??1 MeV to a few tens of GeV. We consider spectrometers and detectors constructed in various laboratories for neutron measurements in numerous fundamental and applied studies. We discuss the results of works devoted to the development of experimental methods and the elaboration of new detectors. We pursue some promising avenues of further investigations.     

GaS multi-walled nanotubes from the lamellar precursor

Inorganic fullerene-like (IF) nanotubes constructed from layered metal chalcogenides are of particular significance because of their excellent physical properties and potential application in wide fields. But very few previous studies were focused on the IF nanotubes of layered III-VI semiconductor. Therefore we investigate the preparation, structure and photoluminescence (PL) properties of GaS nanotube (an important III-VI semiconductor IF nanotube). A simple method is introduced to prepare GaS multi-walled nanotubes for the first time by annealing the natural lamellar precursor in Ar. The reaction temperature is crucial for the formation of nanotube. A suitable temperature range is 500–850 °C. Bulk quantities of GaS nanotubes with diameters of 30–150 nm and lengths up to ten micrometers were produced. Some of these nanotubes show corrugated and interlinked structure and form many segments, demonstrating a bamboo-like structure. As compared to bulk materials, the obvious distinction of the products in PL spectra at liquid nitrogen temperature of 77 K was due to the structure variety. PACS 61.46.+w; 81.07.De; 81.16.Be     

50~250 keV质子入射SiC和Si靶时的电子发射特性研究

在中国科学院近代物理研究所兰州重离子加速器国家实验室测量了能量范围为50~250 keV 的质子入射碳化硅靶和硅靶表面的电子发射产额。实验结果发现,两种半导体靶材的电子发射产额随质子入射能量变化趋势均与作用过程中电子能损随质子入射能量的变化趋势相似。通过分析电子发射的能量来源,发现实验中电子发射产额主要由动能电子发射产额贡献,势能电子发射产额可以忽略不计。两种靶材的电子发射产额均近似地正比于质子入射靶材过程中的电子能损,比例系数B随入射能量略有变化。     

Spin Coulomb Dragging Inhibition of Spin-Polarized Electric Current Injecting into Organic Semiconductors

We introduce a one-dimensional spin injection structure comprising a ferromagnetic metal and a nondegenerate organic semiconductor to model electric current polarizations. With this model we analyse spin Coulomb dragging (SCD) effects on the polarization under various electric fields, interface and conductivity conditions. The results show that the SCD inhibits the current polarization. Thus the SCD inhibition should be well considered for accurate evaluation of current polarization in the design of organic spin devices.     

The possibilities of using silicon tracking telescopes with advanced performance for studying pn interaction

The goals of measuring the polarization degree of an accelerator beam, controlling the luminosity, and providing spatial data on the reaction vertex were defined for the development of a detector system based on silicon tracking telescopes. The use of the developed techniques resulted in a time resolution of ～1 ns and an accuracy of ～1–2% for the reconstruction of the kinetic energy of outgoing protons and deuterons in a range of 1.5–50 MeV. The results of experimental and model studies demonstrate that the achieved high performance of the system can be applied to extend the field of physical research with the application of silicon tracking telescopes. This extension includes the experimental study of the issues of the spin physics of pn-interactions by detecting the low-energy products of the pd → ppn, pd → ppΔ⁰, and pd → pd reactions with a novel experimental data.     

Semi-analytical model for the Seebeck coefficient in semiconductors with isotropic DOS given by a power function

The relations for the Seebeck coefficient in a semiconductor with the isotropic density of states given by a power function are introduced within the scope of a semi-analytical model, which is based on the theoretical relations given by the foundations of the semiconductor physics as well as on experimentally defined temperature dependences of various semiconductor characteristics, but does not include any adjustable parameters. Between those characteristics the major role plays the intrinsic carrier concentration. It was demonstrated that although the introduced model is based on the simplified Maxwell-Boltzmann statistic, it is not compromised by this choice. A comparison with experimental data for five different semiconductors proves its ability to provide reliable predictions over a wide range of parameters (temperature, dopant type and concentration) not only for non-degenerated wide bandgap semiconductors (Si, Ge) but also for InAs, which represents partly degenerated narrow bandgap semiconductors with a non-parabolic density of states. Even in the case of a HgCdTe, with its extremely narrow bandgap and complex temperature dependence of the carrier concentration, the model is in good agreement with experimental data. The semi-analytical nature of the introduced model and its dependence on the abundance and reliability of the used experimental data were discussed on the example of Bi₂Te₃. Although the relative deficiency and controversy of the experimental results in this case significantly impede the model’s applicability, it is still able to give at least qualitative predictions, which are nevertheless better than the results of the calculation of the thermopower from first principles. Being primarily addressed to the experimental community, the model provides simple relations in the case of the parabolic non-intrinsic semiconductor for thermoelectric voltage and for optimal dopant concentration for the thermogenerator within the known working temperature range, which can be useful in real-life ‘energy harvesting’ applications.     

Spectral enhancement in optical parametric amplifiers in the saturated regime

We present numerical and experimental studies on a front-end laser system for seeding a sub-picosecond multi-terawatt/petawatt light source based on two highly saturated optical parametric amplifiers. Numerical results showing energy gain, spectral gain, and stability as saturation is approached are presented. An experimental realisation of the system has been constructed, and its performance has been found to be in good agreement with the numerical simulations. The total gain is in excess of 10⁵ over a few picosecond gain window, and the pulse energy is ～100 μJ with 4 % root mean square stability.     

Thermal analysis and expected performance of the low energy instrument on board the HXMT satellite

The Low Energy X-ray Instrument (LE) of the Hard X-ray Modulation Telescope (HXMT) uses the Swept Charge Device (SCD) to detect the X-rays in 1-15 keV. The performance of SCD is vulnerable to temperature. We analyzed the thermal condition of LE at different satellite working attitudes with the Finite Element Method (FEM). It is shown that the angle between the sunlight and the normal line of the barrier should be less them 26°, to keep the SCD detectors working in the required temperature range, i.e. -40 ℃ to -80 ℃. We find that the performance of LE is very stable in this temperature range, with a typical energy resolution of 160 eV at 5.9 keV.     

Low sputter damage of metal single crystalline surfaces investigated with medium energy ion scattering spectroscopy

It was observed clearly that the sputter damage due to Ar⁺ ion bombardment on metal single crystalline surfaces is extremely low and the local surface atomic structure is preserved, which is totally different from semiconductor single crystalline surfaces. Medium energy ion scattering spectroscopy (MEIS) shows that there is little irradiation damage on the metal single crystalline surfaces such as Pt(111), Pt(100), and Cu(111), in contrast to the semiconductor Si(100) surfaces, for the ion energy of 3–7 keV even above 10¹⁶–10¹⁷ ions/cm² ion doses at room temperature. However, low energy electron diffraction (LEED) spots became blurred after bombardment. Transmission Electron Microscopy (TEM) studies of a Pt polycrystalline thin film showed formation of dislocations after sputtering. Complementary MEIS, LEED and TEM data show that on sputtered single-crystal metal surfaces, metal atoms recrystallize at room temperature after each ion impact. After repeated ion impacts, local defects accumulate to degrade long range orders.     

一种测量GaAs-GaAlAs行波激光放大器增益特性的实验方法

本文报导了一种测量光耦合效率η的新实验方法。这个方法是建立于p-n结短路光电流原理上的。本文推导出适合于行波激光放大器的光耦合效率的公式。短路光电流用一检流计测量,利用公式获得光耦合效率的实验值。利用实验所测光耦合效率,测量了行波激光放大器的增益随注入电流变化的规律,其结果和实验符合。另外本文还介绍了在脉冲注入电流条件下测行波半导体激光放大器增益的实验方法。     

46．7MeV／u~（12）C轰击~（197）Au、~（115）In、~（58）

用气体电离室－半导体位置灵敏探测器望远镜测量了４６．７ＭｅＶ／ｕ（１２）Ｃ离子轰击（１９７）Ａｕ，（１１５）Ｉｎ，（５８）Ｎｉ靶时，在大角区发射的从Ｌｉ到Ｍｇ的复杂碎片能谱；由各碎片的能谱提取了蒸发源的温度和碎片发射的最可几动能Ｅｐ，并与＝Ｖｃｏｕｌ＋２Ｔ计算的平均动能进行了比较，发现实验上提取的最可几动能Ｅｐ总是低于计算的．用Ａ．Ｆｒｉｅｄｍａｎ简单的统计公式对复杂碎片的产额进行粗糙拟合，拟合结果令人满意．     

Single-electron transistor with an island formed by several dopant phosphorus atoms

We present the results of an experimental study of electron transport through individual phosphorus dopants implanted into a silicon crystal. We developed an original technique for single-electron transistor fabrication from silicon-on-insulator material with an island formed by single phosphorus atoms. The proposed method is based on well-known CMOS compatible technological processes that are standard in semiconductor electronics and may be used in most research groups. The large Coulomb blockade energy value of the investigated single-electron transistor (～20 meV) allows one to observe single-electron effects in a wide temperature range up to 77 K. We measured and analyzed stability diagrams of fabricated experimental structures. We demonstrated a single-electron transistor with controllable electron transport through two to three phosphorus dopants only.