New insights into SNR evolution revealed by the discovery of recombining plasmas

We report the discovery of recombining plasmas in three supernova remnants (SNRs) with the Suzaku X-ray astronomy satellite. During SNR’s evolution, the expanding supernova ejecta and the ambient matter are compressed and heated by the reverse and forward shocks to form an X-ray emitting hot plasma. Since ionization proceeds slowly compared to shock heating, most young or middle-aged SNRs have ionizing (underionized) plasmas. Owing to high sensitivity of Suzaku, however, we have detected radiative recombination continua (RRCs) from the SNRs IC 443, W49B, and G359.1–0.5. The presence of the strong RRC is the definitive evidence that the plasma is recombining (overionized). As a possible origin of the overionization, an interaction between the ejecta and dense circumstellar matter is proposed; the highly ionized gas was made at the initial phase of the SNR evolution in dense regions, and subsequent rapid adiabatic expansion caused sudden cooling of the electrons. The analysis on the full X-ray band spectrum of IC 443, which is newly presented in this paper, provides a consistent picture with this scenario. We also comment on the implications from the fact that all the SNRs having recombining plasmas are correlated with the mixed-morphology class.     

The effects of proton radiation on UHMWPE material properties for space flight and medical applications

Ultra High Molecular Weight Polyethylene (UHMWPE) is a polymer widely used as a radiation shielding material in space flight applications and as a bearing material in total joint replacements. As a long chain hydrocarbon based polymer, UHMWPE’s material properties are influenced by radiation exposure, and prior studies show that gamma irradiation is effective for both medical sterilization and increased wear resistance in total joint replacement applications. However, the effects of space flight radiation types and doses on UHMWPE material properties are poorly understood. In this study, three clinically relevant grades of UHMWPE (GUR 1020, GUR 1050, and GUR 1020 blended with Vitamin E) were proton irradiated and tested for differences in material properties. Each of the three types of UHMWPE was irradiated at nominal doses of 0 Gy (control), 5 Gy, 10 Gy, 20 Gy, and 35 Gy. Following irradiation, uniaxial tensile testing and thermal testing using Differential Scanning Calorimetry (DSC) and Dynamic Mechanical Analysis (DMA) were performed. Results show small but significant changes in several material properties between the control (0 Gy) and 35 Gy samples, indicating that proton irradiation could have a effect on the long term performance of UHMWPE in both medical and space flight applications.     

辐射器展开角度对航天器热控能力影响的研究

为了在有限的结构尺寸下提高航天器热控系统的散热能力，提出与流体回路耦合的可展开式辐射器热控方案，建立可展开式辐射器空间散热模型，分析辐射器不同展开角度下系统的热控特性。结果表明，随着辐射器展开角度的变化，辐射器吸收的空间热流也随之发生变化，并最终决定热控回路的流量分配。在工程应用中，基于热控流体回路，通过调节可展开式辐射器的展开角度，可以有效提高航天器热控系统的能力范围。     

How Galactic Cosmic Ray models affect the estimation of radiation exposure in space

The radiation environment in space is a major concern for human spaceflight because of the adverse effects of high levels of radiation on astronauts’ health. Therefore, it is essential to perform radiation risk assessments already during the concept studies of a manned mission. Galactic Cosmic Rays (GCR) have been identified to be one of the primary sources of radiation exposure in space.     

Utilization of CAM,CAF, MAX,and FAX for space radiation analyses using HZETRN

To estimate astronaut health risk due to space radiation, one must have the ability to calculate various exposure-related quantities that are averaged over specific organs and tissue types. Such calculations require computational models of the ambient space radiation environment, particle transport, nuclear and atomic physics, and the human body. While significant efforts have been made to verify, validate, and quantify the uncertainties associated with many of these models and tools, relatively little work has focused on the uncertainties associated with the representation and utilization of the human phantoms. In this study, we first examine the anatomical properties of the Computerized Anatomical Man (CAM), Computerized Anatomical Female (CAF), Male Adult voXel (MAX), and Female Adult voXel (FAX) models by comparing the masses of various model tissues used to calculate effective dose to the reference values specified by the International Commission on Radiological Protection (ICRP). The MAX and FAX tissue masses are found to be in good agreement with the reference data, while major discrepancies are found between the CAM and CAF tissue masses and the reference data for almost all of the effective dose tissues. We next examine the distribution of target points used with the deterministic transport code HZETRN (High charge (Z) and Energy TRaNsport) to compute mass averaged exposure quantities. A numerical algorithm is presented and used to generate multiple point distributions of varying fidelity for many of the effective dose tissues identified in CAM, CAF, MAX, and FAX. The point distributions are used to compute mass averaged dose equivalent values under both a galactic cosmic ray (GCR) and solar particle event (SPE) environment impinging isotropically on three spherical aluminum shells with areal densities of 0.4 g/cm², 2.0 g/cm², and 10.0 g/cm². The dose equivalent values are examined to identify a recommended set of target points for each of the tissues and to further assess the differences between CAM, CAF, MAX, and FAX. It is concluded that the previously published CAM and CAF point distributions were significantly under-sampled and that the set of point distributions presented here should be adequate for future studies involving CAM, CAF, MAX, or FAX. It is also found that the errors associated with the mass and location of certain tissues in CAM and CAF have a significant impact on the mass averaged dose equivalent values, and it is concluded that MAX and FAX are more accurate than CAM and CAF for space radiation analyses.     

Toroidal magnetic fields for protecting astronauts from ionizing radiation in long duration deep space missions

Among the configurations of superconducting magnet structures proposed for protecting manned spaceships or manned deep space bases from ionizing radiation, toroidal ones are the most appealing for the efficient use of the magnetic field, being most of the incoming particle directions perpendicular to the induction lines of the field. The parameters of the toroid configuration essentially depend from the shape and volume of the habitat to be protected and the level of protection to be guaranteed. Two options are considered: (1) the magnetic system forming with the habitat a unique complex (compact toroid) to be launched as one piece; (2) the magnetic system to be launched separately from the habitat and assembled around it in space (large toroid).     

迭代MoM—PO混合方法分析电大载体上多天线系统的辐射特性

各类金属载体上线天线的特性分析具有很重要的实用价值。文章取线天线为矩量法区，电大载体为物理光学法区，将载体对线天线的影响用物理光学法电流合并到矩量法区，使矩量法解决天线．载体系统成为可能。结果表明，混合方法能够快速有效地分析电大尺寸载体上多天线系统的辐射特性。     

Characterization of the near Earth radiation environment by Liulin type spectrometers

Comprehensive study of the dose, flux and deposited energy spectra shape data obtained by Liulin type spectrometers on spacecraft (five different experiments) and aircraft since 2001 is performed with the aim of understanding how well these parameters can characterize the type of predominant particles and their energy in the near Earth radiation environment. Three different methods for characterisation of the incoming radiation from Liulin spectrometers are described. The results revealed that the most informative one is by the shape of the deposited energy spectra. Spectra generated by Galactic Cosmic Rays (GCR) protons and their secondaries are with linear falling shape in the coordinates deposited energy/deposited per channel dose rate. The position of the maximum of the deposited energy spectra inside the South Atlantic Anomaly (SAA) region depends on the incident energy of the incoming protons. Spectra generated by relativistic electrons in the outer radiation belt have a maximum in the first channels. For higher energy depositions these spectra are similar to the GCR spectra. Mixed radiation by protons and electrons and/or bremsstrahlung is characterized by spectra with 2 maxima. All type of spectra has a knee close to 6.2 MeV deposited energy, which correspond to the stopping energy of protons in the detector. Dose to flux ratio known also as specific dose is another high information parameter, which is given by experimentally obtained formulae [Heffner, J. Nuclear radiation and safety in space. M. Atomizdat. 115, 1971 (in Russian)] connecting the dose to flux ratio and the incident energy of the particles.     

等离子体天线的原理及特性

根据等离子体柱天线的系统构成,分析了等离子体柱天线的基本工作原理,讨论了表面波在等离子体柱天线中的传播特性、等离子体柱内的电子分布,以及天线的长度、噪声与辐射特性。分析表明：表面波能激发和维持等离子体柱,等离子体柱可构成等离子体天线,且具易隐身、可控性等优点。