行星际空间质子引起介质深层充电的GEANT4模拟研究

高通量的空间质子是导致行星际航天器深层充电的主要原因,基于辐射诱导电导率模 型（RIC）和粒子输运模拟工具GEANT4对介质材料在质子辐照条件下的深层充电问题进行了 预估。利用GEANT4-RIC充电计算方法,首先计算出10MeV质子在Kapton和Teflon中的注量和 剂量沉积曲线,进而根据电流连续性方程、泊松方程和电荷俘获方程组成的辐射诱导电导率 模型（RIC）求解出介质内电荷和电场分布,与介质击穿电场阈值对比作为其是否发生放电 的依据。模拟结果证实了对10MeV质子,在质子注量为3×10 12 ／cm 2时Kapton会发 生放电,而Teflon则不会发生放电的一般性试验结论。验证了GEANT4-RIC方法用于行星际航 天器介质材料质子充放电评价的可行性,为此类问题的解决奠定了基础。
     

空间高能粒子与器件布线层核反应后次级粒子LET分布研究

空间高能质子和重离子是导致元器件发生单粒子效应的根本原因,为准确评估元器件在轨遭遇的单粒子效应风险,必须清楚高能质子、重离子与器件材料发生核反应的物理过程及生成的次级重离子LET（Line EnergyTransfer）分布规律。针对典型CMOS工艺器件模拟计算了不同能量质子和氦核粒子在器件灵敏单元内产生的反冲核、平均能量及线性能量转移值,并分析了半导体器件金属布线层中重金属对次级重离子LET分布的影响规律。计算结果表明：高能粒子与器件相互作用后产生大量次级重离子,且高能质子作用后产生的次级粒子的LET值主要分布为0～25MeV·cm²/mg;高能氦核粒子作用后产生的次级粒子的LET值主要分布为0～35 MeV·cm²/mg;有重金属钨（W）存在时能提高次级粒子的LET值,增加了半导体器件发生单粒子效应的概率,该研究结果可为元器件单粒子效应风险分析、航天器抗单粒子效应指标确定提供重要依据。     

Gamma-ray detector on board lunar mission Chang’E-1

Gamma-ray spectrometer (GRS) is included in the payload of Chinese first lunar mission Chang’E-1 that will be launched in 2007. Specific objectives of the GRS are to map abundance of O, Si, Fe, Ti, U, Th, K, and perhaps, Mg, Al, and Ca to depths of about 20 cm. There are remarkable advantages for GRS application to remote sensing elemental materials over the entire lunar surface: large effective area and good ability for background rejection. We will describe the design of GRS and present its performance in this paper. Moreover, the GRS calibration will also be introduced.     

Monte Carlo simulations of CASSINI/LEMMS

In an effort to characterize the response of the low energy magnetospheric measurements system (LEMMS) on the CASSINI spacecraft to energetic ions and electrons we have taken advantage of the excellent pre-launch beam calibrations in comparison to an extensive series of electron and ion Monte Carlo simulations. We selected the geometry and tracking toolkit to provide the framework for the instrument modeling and simulation environment. The results from these simulations match very well with the data collected during the instrument calibration. This gives us confidence that this simulation toolkit handles both electron and ion interactions in a reasonable fashion and that we can successfully apply this tool to regions of the spectrum where calibration data is not available.     

Multiple Coulomb scattering method to reconstruct low-energy gamma–ray direction in the GAMMA-400 space-based gamma–ray telescope

The GAMMA-400 currently developing space-based gamma-ray telescope is designed to measure the gamma-ray fluxes in the energy range from ～20?MeV to several TeV in the highly elliptic orbit (without shadowing the telescope by the Earth) continuously for a long time. The physical characteristics of the GAMMA-400 gamma-ray telescope, especially the angular and energy resolutions (at 100-GeV gamma rays they are ～0.01° and ～1%, respectively), allow us to consider this space-based experiment as the next step in the development of extraterrestrial high-energy gamma-ray astronomy. In this paper, a method to improve the reconstruction accuracy of incident angle for low-energy gamma rays in the GAMMA-400 space-based gamma-ray telescope is presented. The special analysis of topology of pair-conversion events in thin layers of converter was performed. Applying the energy dependence of multiple Coulomb scattering for pair components, it is possible to estimate the energies for each particle, and to use these energies as weight in the angle reconstruction procedure. To identify the unique track in each projection the imaginary curvature method is applied. It allows us to obtain significantly better angular resolution in comparison with other methods applied in current space-based experiments. When using this method for 50-MeV gamma rays the GAMMA-400 gamma-ray telescope angular resolution is about 4°.     

Monte Carlo calibration of the response of the University of Chicago’s Cosmic Ray Nuclei Experiment (CRNE) on IMP-8 to electrons above 0.5 MeV

Modern instrument-simulation techniques offer the possibility of increasing the scientific yield from archival space datasets. In this paper, we report on a simulation of the electron response of the University of Chicago’s Cosmic Ray Nuclei Experiment (CRNE) instrument on the IMP-8 satellite. IMP-8/CRNE returned data from 1973 to 2006. The CRNE particle telescope was designed to measure the isotopic composition of Galactic cosmic-ray (GCR) nuclei and has also been used in many studies of protons and ions above 10 MeV/nucleon from solar energetic particle (SEP) events. But CRNE also functions as a highly-capable detector for solar electrons above 0.5 MeV, an energy range that has not been extensively studied. Utilization of the CRNE electron data has heretofore been limited by the fact that CRNE was never calibrated for electrons. We have therefore used the GEANT4 Monte Carlo simulation package to model the CRNE response to electrons and (separately) protons for multiple energies and incident angles. The results were used to compute the energy- and angle-dependence of the effective area and the energy-dependence of the geometric factor. The response to protons, which was already well understood, was used to verify the mass model, the simulation settings, and the post-processing software. Our simulation of the IMP-8/CRNE electron response now allows analysis of hundreds of relativistic solar electron events observed by CRNE over the years, including studies of evolution of electron energy spectra with high time resolution. We show examples of these results and briefly discuss potential applications to future scientific investigations.