3 MeV质子辐照对AlGaN/GaN高电子迁移率晶体管的影响

研究了AlGaN/GaN 高电子迁移率晶体管(HEMT)的质子辐照效应. 在3 MeV质子辐照下, 当辐照剂量达到1× 10¹⁵ protons/cm²时, 漏极饱和电流下降了20%, 最大跨导降低了5%. 随着剂量增加, 阈值电压向正向漂移, 栅泄露电流增加. 在相同辐照剂量下, 1.8 MeV质子辐照要比3 MeV质子辐照退化严重. 从SRIM软件仿真中得到不同能量质子在AlGaN/GaN异质结中的辐射损伤区, 以及在一定深度形成的空位密度. 结合变频C-V测试结果进行分析, 表明了质子辐照引入空位缺陷可能是AlGaN/GaN HEMT器件电学特性退化的主要原因.     

石英玻璃低能质子辐照损伤动力学研究

地面模拟研究了JGS3光学石英玻璃在真空、热沉和能量低于200keV的低能质子辐照下表面光学性能变化的基本规律．并建立了辐照损伤色心演化的动力学唯象模型。试验结果表明．大通量低能质子辐照对石英玻璃表层具有明显的表面损伤效应。随着辐照吸收剂量的增加,光密度变化先以线性规律迅速增加．加进一步增加时逐渐呈现饱和趋势;采用较高能量辐照作用后光密度变化出现饱和趋势的拐点提前,且饱和数值降低。根据对试验结果的分析,建立了低能质子辐照下石英玻璃色心演化的动力学模型．并给出了光密度变化的表达式。采用模型结果进行数学模拟,模拟曲线与试验结果曲线相似。因此所建立的动力学模型可以用来定量描述低能质子辐照下石英玻璃光学性能随辐照吸收剂量的变化规律。     

Damage distribution and measure of projected range in proton bombarded GaAs

Abstract

The technique of cross-sectional transmission electron microscopy has been applied to obtain information on the projected range of protons and their damage distribution in gallium arsenide. The crystals were subjected to dosages of 1 × 10¹⁵ to 1 × 10¹⁷ protons cm^?2 and proton energies of 100, 200 and 300 keV. Within this energy range the damage shows a Gaussian distribution about a mean range which correlates closely with LSS values. The experimentally determined damage profiles are found to be essentially independent of proton energy and the temperature of post implantation anneal for a given dosage. The displacement damage as reflected by the damage profiles is found to be linear with proton dose. Finally, it is estimated that defects became visible in unannealed crystals when each atom is, on the average, displaced at least once during irradiation.     

质子束治疗中非均匀组织的等效水厚度修正研究

非均匀组织等效水厚度修正是研究质子放射治疗的重要组成部分, 利用蒙特卡罗Fluka2011.2程序模拟了不同能量(50–250 MeV)的质子束入射到不同介质中的输运过程, 总结出了在不同介质中质子束初始能量与质子束Bragg峰深度关系, 并拟合出质子束在介质中的等效水厚度修正公式. 结果表明, 对不同能量的质子束入射到非均匀组织中, 通过拟合公式计算出Bragg峰深度值与Fluka模拟的质子束Bragg峰的位置相差在1 mm 之内. 如果建立起介质和水的Bragg峰比与电子密度比关系的数据库, 该公式有可能用于临床上的质子放射治疗的剂量计算中. 关键词： 蒙特卡罗 质子治疗 等效水厚度 Bragg 峰     

Effect of proton irradiation on the physical properties of PC/PBT blends

Samples from polycarbonate/poly (butylene terephthalate) (PC/PBT) blends film have been irradiated using different fluences (1?×?10¹⁵– 5?×?10¹⁷ H⁺/cm²) of 1?MeV protons at the University of Surrey Ion Beam Center, UK. The structural modi?cations in the proton irradiated samples have been studied as a function of fluence using different characterization techniques such as X-ray diffraction and UV spectroscopy. The results indicate that the proton irradiation reduces the optical energy gap that could be attributed to the increase in structural disorder of the irradiated samples due to crosslinking. Furthermore, the color intensity ΔE, which is the color difference between the non-irradiated sample and those irradiated with different proton fluences, increased with increasing the proton fluence up to 5?×?10¹⁷ H^+/cm², convoyed by an increase in the red and yellow color components. In addition, the resultant effect of proton irradiation on the thermal properties of the PC/PBT samples has been investigated using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). It is found that the PC/PBT decomposes in one weight loss stage. Also, the variation of transition temperatures with proton fluence has been determined using DSC. The PC/PBT thermograms were characterized by the appearance of two endothermic peaks due to the glass transition and melting temperatures. The melting temperature of the polymer, T_m, was investigated to probe the crystalline domains of the polymer, since the proton irradiation destroys the crystalline structure so reducing the melting temperature.     

Laser-induced ion acceleration at ultra-high laser intensities

Ion acceleration by ultrashort laser pulses of very high intensities of the order 10²²?W/cm² is studied by two-dimensional Particle-In-Cell simulations. We show that laser normal incidence is preferred for such high intensities. For linearly polarized laser radiation, higher maximum proton/ion energies are achieved than for circular polarization. For linear polarization, the transition from the target normal sheath acceleration to the acceleration on the target front side by the radiation pressure is analyzed in detail. The transition intensity is increasing with the target thickness. The radiation pressure dominated regime leads to considerably higher number of accelerated protons and thus to a higher acceleration efficiency.     

Average excited state lifetimes in 73Br

Lifetimes in the region of 10^?16 s have been measured for excited states between 4 and 6.6 MeV in ⁷³Br. The states were produced by the β⁺(EC) decay of a mass-separated source of ⁷³Kr, and they decayed by the emission of protons or γ-rays; their lifetimes were measured by the particle X-ray coincidence technique. The data yield information on both γ-ray and proton partial widths as well as on the level density, a level density parameter-a = 13.7 MeV^?1 is obtained. With the level widths so determined, a statistical model calculation yields excellent agreement with the delayed proton spectrum if a smooth gaussian β-strength function is employed. It is concluded, however, that without the lifetime data, β-strength function information could not have been reliably extracted.     

Features of changes in the surface structure of K-208 glass under electron—proton irradiation

Changes in the surface structure of K-208 glass after single-time irradiation of its samples with 20-keV electrons and protons are studied using atomic-force microscopy. Irradiation is performed in a vacuum chamber under a pressure of 10^–4 Pa; the densities of the electron (? _e ) and proton (? _р ) fluxes are varied in the range of 10¹⁰–2.5 × 10¹¹ cm^?2 s^?1. Analysis of the samples irradiated in the case where the parameters ? _e and ? _р increased in a stepwise manner makes it possible to study the appearance, growth, and evolution of microscopic structures on their surfaces. The radiation-stimulated processes of defect annealing and the release and field diffusion of alkali metal ions are accompanied by crystallization of the irradiated glass layer, which gives grounds for the use of dislocation mechanisms for mass transfer in explaining the formation of microprotrusions on its surface. It is shown that the character of changes in the structure is determined by the values of the parameters ? _e and ? _р and the ratio between them. In particular, it is established that, in the case of electron— proton irradiation of the glass, electrostatic discharges begin to noticeably affect the formation of microprotrusions for ? _е > 3? _р .     

Nucleons produced in inelastic electron scattering with a deuterium target

We have measured at ?k² = 0.6 (GeV/c)² and W = 2.3 GeV the inclusive electroproduction cross sections for final-state neutrons and protons from a deuterium target. By comparison with previous data from a proton target, we present cross sections for inclusive nucleon production from neutrons which show great similarity to those from protons. There is evidence that ?⁰ production is present with essentially the same strength as with a proton target.     

First results of electron cooling experiments at LEAR

The first results are presented of electron cooling experiments in the Low-Energy Antiproton Ring (LEAR) at CERN, performed with a proton beam of about 50 and 21 MeV. The number of stored protons ranged from 10⁷ to 3 × 10⁹. Cooling times of the order 1 s and proton drag rates of up to 0.7 MeV/s were obtained. The capture of cooling electrons by protons producing hydrogen atoms was used to derive an effective electron temperature (0.25 eV). From the angular profile of the neutral hydrogen beam an upper limit of 3π mm.mrad could be deduced for the horizontal equilibrium proton-beam emittance. The lowest equilibrium momentum spread was 2 × 10⁵ (FWHM), as derived from the analysis of the longitudinal Schottky signal. This Schottky signal exhibited an unusual behaviour with beam intensity and under certain conditions showed a doublepeak structure which was associated with collective beam noise. For very cold beams transverse instabilities were observed, which resulted in a rapid spill-off of protons and a stabilization at lower intensities. The threshold of these instabilities was raised by heating the proton or the electron beam. The cooling of a bunched proton beam was investigated. The reduction of the proton momentum spread led to bunch lengths of about 2 m, containing 3 × 10⁸ protons.     

入射电子能量对低密度聚乙烯深层充电特性的影响

高能带电粒子与航天器介质材料相互作用引起的深层带电现象, 一直是威胁航天器安全运行的重要因素之一. 考虑入射电子在介质中的电荷沉积、能量沉积分布以及介质中的非线性暗电导和辐射诱导电导, 建立了介质深层充电的单极性电荷输运物理模型. 通过求解电荷连续性方程和泊松方程, 可以得出不同能量 (0.1–0.5 MeV) 电子辐射下, 低密度聚乙烯 (厚度为1 mm) 介质中的电荷输运特性. 计算结果表明, 不同能量的电子辐射下, 介质充电达到平衡时, 最大电场随入射能量的增加而减小; 同一能量辐射下, 最大电场随束流密度的增大而增加. 入射电子能量较低时 (≤ 0.3 MeV) , 最大电场随束流密度的变化趋势基本相同. 具体表现为: 当束流密度大于3× 10^-9 A/m²时, 最大场强超过击穿阈值2×10⁷ V/m, 发生静电放电 (ESD) 的可能性较大. 随着入射电子能量的增加, 发生静电放电 (ESD) 的临界束流密度增大, 在能量为0.4 MeV时, 临界束流密度为6×10^-8 A/m². 当能量大于等于0.5 MeV时, 在束流密度为10^-9–10^-6 A/m²的范围内, 均不会发生静电放电 (ESD) . 该物理模型对于深入研究深层充放电效应、评估航天器在空间环境下 深层带电程度及防护设计具有重要的意义. 关键词： 高能电子辐射 低密度聚乙烯(LDPE) 介质深层充电 电导特性     

Elektronendichten und Elektronentemperaturen bei Verdichtungsstößen

Electromagnetically driven shock-waves of about Mach 50 in Helium have been spectroscopically analysed. Shape and relative intensities of the HeII-3203 and HeI-5876 lines and continuum have been measured during the first microsecond following the luminous front. From 0.15 μsec up to 0.85 μsec after luminous onset electron density decreases from 2.5·10¹⁷cm^?3 to 10¹⁷cm^?3. The electron temperature drops from 4.5 eV to 4.0 eV. Values as calculated byRankine-Hugoniot coincide with experimental results within 10%. From HeI-5876 and HeI-3889 precursor radiation and no corresponding radiation from HeII-lines it is to be concluded that the signals are due to secondary emission.     

Polarization in quasielastic (p,2p) scattering on a 4He nucleus at 1 GeV

The polarization of secondary protons from the (p, 2p) reaction induced by 1-GeV protons incident to a ⁴He nucleus was measured in a kinematically complete experiment. By using a two-arm magnetic spectrometer, two secondary protons from this reaction were recorded in coincidence at unequal scattering angles of Θ₁ = 18°?24.21° and Θ₂ = 53.22° over a broad range of the recoil-nucleus momentum K _B between 0 and 150 MeV/c. It was found that the measured polarization of either secondary proton is less than that observed in free elastic proton-proton scattering. The magnitude of this difference is determined by the mean binding energy of s-shell protons rather than by the effective nuclear density. The polarizations measured in inclusive quasielastic and elastic scattering of 1-GeV protons on ⁴He nuclei are presented for scattering angles in the range Θ₁ = 18° ? 24.21°.     

Systematics of (p,p′) and (p, α) spectra from 14 MeV proton bombardment of medium-A targets

Differential cross sections have been measured between 30° and 150° for the (p, p′) and (p, α) reactions induced by 14 MeV protons in the following targets: ³⁵Mn, ³⁶Fe, ⁵⁸Ni, ⁵⁹Co, ⁶²Ni, ⁶³Cu and ⁶⁴Zn. The results have been compared with the spin-dependent statistical theory and good agreement was obtained for the (p, α) reactions with a level density parameter a = (0.138±0.008)A MeV^?1. This value is substantially lower than that obtained in a spin-independent analysis of the same data. The agreement of the (p, p′) spectra with theory is poor and it is found that a 15–40% contribution from precompound emission is required. The emission of low-energy protons from the (p, np) reaction was observed in all cases and comparison of the cross sections with these of the corresponding (p, n) reactions yields information on the competition between γ-ray and proton emission.     

Build-up of F and M color centers in KCl single crystals under combined electron and proton irradiation

The F and M color-center build-up kinetics in KCl crystals under combined irradiation with electrons of energy 15 and 100 keV and 100-keV protons have been studied in the flux range of 10¹³–10¹⁵ cm⁻² and at a flux density of 3×10¹¹ cm⁻² s⁻¹. It is shown that consecutive irradiation with electrons and protons produces results not obtainable under electron or proton irradiation alone. Fiz. Tverd. Tela (St. Petersburg) 40, 2015–2018 (November 1998)     

用20—1020 keV单能质子刻度CR-39固体核径迹探测器

用北京师范大学2×1.7MV串列加速器和400 kV高压倍加器产生的20—1020 keV单能质子束对CR-39固体核径迹探测器进行了刻度.为了保证质子的单能性和固体核径迹探测器上径迹密度不能超过10⁶/cm²的要求,对两台加速器分别采用了不同方法控制质子辐照数量.在串列加速器上采用了狭缝加转盘的方法,在高压倍加器上采用了100 ns单次高压脉冲扫描束流的方法,既保持了质子的单色性,又达到了质子注量小于10⁶/cm²的 关键词： 单能质子 固体核径迹探测器 CR-39     

The muon depolarization rate in β-palladium hydride

A depolarization rate σ = 0.1205 ± 0.0050 μsec^?1, due to the proton nuclear dipolar fields, was observed for polarized muons implanted in Pd-H_0.97 in the β phase, at temperatures below 50 K, independent of temperature and applied field. The results indicate that the muon substitutes for one of the protons, and that nearest-neighbor protons are at octahedral lattice sites. On comparing our results with recent NMR data, it appears that the mean muon-proton nearest neighbor distance is significantly larger than that between protons alone. Also, a search for muon local moment magnetism gave a null result.     

Multiparticle production in the Fermilab bubble chambers

In the past two years many new data have been collected from experiments in the Fermi National Accelerator Laboratory bubble chambers. While some of the important new results are from second generation, high statistics pp experiments, much of the new data come from interactions initiated by π^± and $\text{p}$ beams on proton targets. In addition, preliminary results are now available from interactions of K^± with protons, π⁺ and protons with deuterium, and π^? with neon. In this review of experimental results on multiparticle production, as studied in the bubble chamber, these data are summarized and comparisons are made among the different incident projectile and target reactions.     

Experiment on the electromagnetic radiation excited in an electron beam‐ion channel system

An experimental study on electromagnetic (EM) radiation in an electron beam‐ion channel system is reported, which indicates the same result predicted by our previous theory. The system is formed in an arc plasma jet with a plasma density of 10¹⁷m^?3 , and the electron beam is driven by a voltage pulse of 20 kV. The result shows that the system can excite EM radiation in the range of the plasma frequency. The scheme is also hopeful to be used for generating high‐frequency and wide‐band EM radiation up to terahertz by enhancing the plasma density.     

Excited state dynamics in silver nanoparticles embedded in phosphate glass

Excited state dynamics in silver nanoparticles embedded in aluminophosphate glass was studied by ultrafast optical pump–probe technique. The absorption process of pump radiation and the electron–phonon relaxation on the 10^?13–10^?11 s scale were analyzed in the framework of two-temperature model. The time evolution of the light-induced transient diffraction grating shows an uncommon relaxation on the nanosecond time scale. This relaxation is assigned to phonon–phonon scattering process as well as to the energy transfer from photoexcited electronic states in glass matrix to silver nanoparticles.