卫星舱内粒子注量和剂量的关系

为探讨卫星舱内粒子注量和剂量关系，利用返回式卫星舱内计数管型个人测量仪和ＬｉＦ热释光剂量计的辐射剂量测量的结果，研究了仪器显示计数同剂量的关系，对粒子的注量和平均阻止本领做出估计。研究结果表明，仪器计数和粒子注量同剂量的关系可通过一个转换系数对应起来，且测点周围屏蔽对这一系数的影响不明显，舱内粒子的平均能量很高，主要成分是银河宇宙辐射。     

近地轨道卫星舱内辐射测量

在我国１９９２年１０月发射的返回式卫星舱内，测量的７ｄ累积辐射剂量为０．７４ｍＧＹ，平均日剂量为０．１１ｍＧＹ，舱内次级热中子注量为１．３×ｌ０４～２．３×ｌ０４ｎ／ｃｍ２，平均日通量为１．９×１０４～３．３×１０４ｎ／ｃｍ２，重核粒子径迹密度为１２～１５径迹／ｃｍ２．ｄ－１。研究发现，质量厚度不同的卫星头部与裙部的剂量水平无显著差异，说明３００ｋｍ左右的近地轨道飞行器舱内辐射剂量主要来自银河宇宙线。     

卫星舱内电离辐射强度的动态变化

为探讨卫星舱内电离辐射强度的动态变化，用单片机定时采集个人辐射剂量计的计数脉冲，自动存储在电擦除只读存储器中，组成微型的电离辐射强度动态数据记录装置，搭载于我国的返回式卫星上，成功地测得了舱内电离辐射强度随卫星飞经的空域不同而变化的动态数据。     

利用MRI三维男性人体模型对航天员所受空间辐射的估算

目的 建立空间辐射环境下,航天员器官所受辐射剂量及对其健康危险的计算方法.方法 利用符合航天员体征的人体MRI图像,建立三维男性人体模型及辐射数据库,并结合蒙特卡罗粒子输运程序GEANT4用于剂量计算.结果 我们得到了模拟各向同性抽样情况下,10 MeV到500 MeV单个质子对人体辐射敏感器官的吸收剂量及有效剂量.结论 在航天员体征三维人体模型及辐射数据库的基础上.利用空间舱内测量质子谱,得到了舱内累计剂量.计算的皮肤剂量为148.6 μGy/d.该值与美国和俄罗斯发表的数据100-300μGy/d比较接近.     

小型生物舱环境参数记录器的研制

为长时间地动态测量，记录小型生物舱内的温度和离心机的转速，设计了一种采用单片机控制的环境参数记录器，利用单片机内部定时器和Ａ／Ｄ转换器，间隔半小时交替测量舱温和离心机转速并将数据存储在数据存储器２８Ｃ６４中，试验表明，利用低功耗新型ＰＩＣ单片机控制的记录器适用于卫星塔载实验。     

空间电子辐射风险及其防护策略研究进展

在外辐射带运行的卫星受到空间天气变化的影响较大,如何保障这些卫星长期健康运行是工程部门面临的最大挑战。本文首先分析了空间外辐射带电子动态分布规律以及空间电子辐射对原材料和元器件可能造成的辐射风险,回顾了目前国内外常用的空间电子防护技术与防护策略。在此基础上提出卫星电子辐射风险管理是一个系统工程:发射前,利用空间辐射环境模型和效应进行风险预估,指导卫星和有效载荷的抗辐射工程设计;在轨飞行中,实时监测空间辐射环境和有效载荷辐射效应数据,为地面飞行控制决策系统提供依据,采取合适的防护措施保障在轨卫星的安全;飞行任务后,通过对任务期间数据的积累与分析,完善模型与工程设计参数,形成一个封闭、有效运行的系统。     

中倾角近地轨道载人航天辐射危险性分析

为了解５００ｋｍ以下，倾角为４０°～５０°的近地轨道载人航天辐射危险性。按照已知太阳质子事件参数的轨道飞行器舱内辐射剂量实际测量结果对其他大事件进行估计，结果表明，迄今为止的太阳质子事件不会对如此轨道载人飞行的辐射安全构成威胁。     

用于卫星搭载的小型生物舱

为进行空间生命科学探索研究，研制成功用于返回式卫星搭载的小型生物舱。舱体为全密封铝合金结构。舱内用超氧化钾和氢氧化锂自动平衡供氧。舱壳夹层中充填相变材料，实施被动式保温，舱内设置有失重自启动离心机，为空间科学实验提供模拟重力条件。微电子学器件由干电池供电，对离心机作稳速控制。     

回收卫星舱内辐射剂量测量

本文叙述了我国初期的回收卫星舱内辐射剂测量。在舱内五个不同位置上安放了被动辐射剂量计包,选用的剂量计是氟化锂(锂-6和锂-7两种)剂量计和荧光玻璃剂量计。在一些氟化锂剂量计周围加了不同厚度的铝屏蔽以提供一定的入射带电粒子的能量截断。结果表明,舱内宇宙辐射剂量水平与位置和屏蔽厚度有关,测量的舱内剂量水平为(10.3—18.1)×10~(-5)/kg(40—70mR)等效照射量/天。     

卫星生物搭载舱的辐射剂量测量及蚕卵生物叠试验

本文利用LiF热释光剂量计对我国生物搭载舱内外宇宙辐射剂量作了监测研究。经过八天的近地轨道飞行,舱内累积辐射剂量约为0.53±0.04mGy,平均日剂量约为0.07mGy/d。舱内辐射剂量主要是能量为50MeV 以上的高能质子形成的。这一剂量水平比地面高27倍,但未超过最大允许剂量,在评价空间生物效应时可作参考。本文还讨论了屏蔽厚度的影响,中子对剂量的贡献及舱内平均日剂量与轨道高度的关系。在生物舱内放置了CR-39塑料核径迹探测器与蚕卵组成的生物叠进行宇宙线重粒子及其生物效应的研究。为判定蚕卵样品是否被重粒子所击中,解决了重粒子射入蚕卵的径迹定位技术。试验表明,生物叠中被重粒子击中的蚕卵孵化率略高于未被击中的蚕卵孵化率,虽因样本量少不能满足统计学要求,但其趋势与国外报导的某些试验结果相一致。     

裂变中子场的比释动能测定

用自行研制的IRM80S-TE1和IRM81T-TE1两种组织等效电离室与用Mullard G-M计数管组装的γ剂量计,组成双探测器,建立了裂变中子-γ混合场比释动能测定方法。测量结果总的估计不确定度为±5.2％。并与用美国FWT IC-17A组织等效电离室所测得的数据进行了比较,三种电离室在裂变中子场中的总响应及中子比释动能的测量结果在±0.4％之内符合。本文所用的测量方法对其它快中子场测量也是适用的。     

Proton Range Uncertainty Due to Bone Cement Injected Into the Vertebra in Radiation Therapy Planning

We wanted to evaluate the influence of bone cement on the proton range and to derive a conversion factor predicting the range shift by correcting distorted computed tomography (CT) data as a reference to determine whether the correction is needed. Two CT datasets were obtained with and without a bone cement disk placed in a water phantom. Treatment planning was performed on a set of uncorrected CT images with the bone cement disk, and the verification plan was applied to the same set of CT images with an effective CT number for the bone cement disk. The effective CT number was determined by measuring the actual proton range with the bone cement disk. The effects of CT number, thicknesses, and position of bone cement on the proton range were evaluated in the treatment planning system (TPS) to draw a conversion factor predicting the range shift by correcting the CT number of bone cement. The effective CT number of bone cement was 260 Hounsfield units (HU). The calculated proton range for native CT data was significantly shorter than the measured proton range. However, the calculated range for the corrected CT data with the effective CT number coincided exactly with the measured range. The conversion factor was 209.6 [HU · cm/mm] for bone cement and predicted the range shift by approximately correcting the CT number. We found that the heterogeneity of bone cement could cause incorrect proton ranges in treatment plans using CT images. With an effective CT number of bone cement derived from the proton range and relative stopping power, a more actual proton range could be calculated in the TPS. The conversion factor could predict the necessity for CT data correction with sufficient accuracy.     

Brain abscesses: etiologic categorization with in vivo proton MR spectroscopy

PURPOSE: To compare the metabolite patterns observed at in vivo proton magnetic resonance (MR) spectroscopy of brain abscesses in patients for whom bacteriologic information was obtained from cultures and to categorize the MR spectral patterns with respect to the underlying etiologic agents. MATERIALS AND METHODS: MR imaging and in vivo single-voxel proton MR spectroscopic data obtained from 75 patients with brain abscesses were retrospectively analyzed. Ex vivo spectroscopic experiments with the pus from 45 of these patients also were performed, and the data were further categorized on the basis of bacteriologic information. Quantification of various metabolites and metabolite ratios and statistical analyses of lactate and lactate/amino acid (AA) ratio levels were performed by using one-way analysis of variance. RESULTS: On the basis of in vivo proton MR spectroscopic and bacteriologic analysis findings, data were classified into three categories: Group 1 data showed resonances of lactate, AAs, and acetate, with or without succinate at proton MR spectroscopy; cultures for this group showed obligate anaerobes or a mixture of obligate and facultative anaerobes. The metabolite patterns in the group 2 and group 3 data were similar to the pattern of the group 1 data, with the exception that acetate and succinate resonances were absent. Culture was positive for either obligate aerobes or facultative anaerobes in group 2 and was sterile in group 3. At analysis of variance, in vivo data showed significant differences in lactate/AA ratios (P =.008), and ex vivo data showed significant differences in lactate levels (P =.001) among the three groups. CONCLUSION: It is possible to differentiate anaerobic from aerobic or sterile brain abscesses on the basis of metabolite patterns observed at in vivo proton MR spectroscopy. This information may be useful in facilitating prompt and appropriate treatment of patients with these abscesses.     

Development of a Monte Carlo track structure code for low-energy protons in water

PURPOSE: The development of a new generation of Monte Carlo track structure code is described, which simulates full slowing down of low-energy proton history tracks (lephist) in the range 1 keV-1 MeV in water. MATERIAL AND METHODS: All primary protons are followed down to 1 keV and all electrons to 1 eV. All primary interactions, including elastic scattering, ionization, excitation and charge exchange processes by protons and neutral hydrogen were taken into account. Cross-sections for proton and hydrogen impact were obtained from experimental data for water. Where data were lacking, the existing experimental data were fitted and extrapolated. The tracks of secondary electrons were generated using the electron track code kurbuc. The cross-sections and the energy transfer data were individually evaluated for the principal interactions induced by protons and hydrogen atoms in water. The analysis starts with the published cross-section data for water using a semi-empirical model including contributions from the neutral hydrogen atoms. For excitation cross-sections, the original Miller-Green analytical formula was used. For ionization by neutral hydrogen atoms, the same energy spectrum was assumed for secondary electrons as for protons. The total cross-sections were taken from the experiment of Blorizadeh and Rudd (1986b, c). For the stripping of charge by neutral hydrogen the data of Toburen et al. (1968) were used. RESULTS: Data are presented on total and differential elastic cross-sections as a function of energy and scattering angle respectively; single and double differential cross-sections for secondary electrons ejected by various energy proton impact; total cross-sections due to proton and hydrogen impact on water; stopping power cross-sections; and fraction of stopping power for water for protons as a functions of proton energy. CONCLUSIONS: Tracks were analysed to provide confirmation on the reliability of the code and information on physical quantities, such as range, W, restricted stopping power, radial dose profiles and some microdosimetric parameters. Model calculations show good agreement with the experimental and calculated data.     

Development of a Monte Carlo track structure code for low-energy protons in water

Purpose : The development of a new generation of Monte Carlo track structure code is described, which simulates full slowing down of low-energy proton history tracks (lephist) in the range 1 keV-1 MeV in water. Material and methods : All primary protons are followed down to 1 keV and all electrons to 1 eV. All primary interactions, including elastic scattering, ionization, excitation and charge exchange processes by protons and neutral hydrogen were taken into account. Cross-sections for proton and hydrogen impact were obtained from experimental data for water. Where data were lacking, the existing experimental data were fitted and extrapolated. The tracks of secondary electrons were generated using the electron track code kurbuc. The cross-sections and the energy transfer data were individually evaluated for the principal interactions induced by protons and hydrogen atoms in water. The analysis starts with the published cross-section data for water using a semi-empirical model including contributions from the neutral hydrogen atoms. For excitation cross-sections, the original Miller-Green analytical formula was used. For ionization by neutral hydrogen atoms, the same energy spectrum was assumed for secondary electrons as for protons. The total cross-sections were taken from the experiment of Blorizadeh and Rudd (1986b, c). For the stripping of charge by neutral hydrogen the data of Toburen et al. (1968) were used. Results : Data are presented on total and differential elastic crosssections as a function of energy and scattering angle respectively; single and double differential cross-sections for secondary electrons ejected by various energy proton impact; total cross-sections due to proton and hydrogen impact on water; stopping power cross-sections; and fraction of stopping power for water for protons as a functions of proton energy. Conclusions : Tracks were analysed to provide confirmation on the reliability of the code and information on physical quantities, such as range, W, restricted stopping power, radial dose profiles and some microdosimetric parameters. Model calculations show good agreement with the experimental and calculated data.     

PET dosimetry in proton radiotherapy: a Monte Carlo study

We have used a Monte Carlo program to evaluate the applicability of positron emission tomography to in vivo dosimetry for proton radiotherapy. The transport program PTRAN was utilized to estimate the distribution of positron emitter nuclei produced by proton nuclear inelastic interactions in tissue. A comparison of Monte Carlo results with experimental data available in the literature shows that PET can be a useful tool in proton radiotherapy especially for in vivo Bragg peak localization.     

Correction of systematic errors in quantitative proton density mapping

Interest in techniques yielding quantitative information about brain tissue proton densities is increasing. In general, all parameters influencing the signal amplitude are mapped in several acquisitions and then eliminated from the image data to obtain pure proton density weighting. Particularly, the measurement of the receiver coil sensitivity profile is problematic. Several methods published so far are based on the reciprocity theorem, assuming that receive and transmit sensitivities are identical. Goals of this study were (1) to determine quantitative proton density maps using an optimized variable flip angle method for T(1) mapping at 3 T, (2) to investigate if systematic errors can arise from insufficient spoiling of transverse magnetization, and (3) to compare two methods for mapping the receiver coil sensitivity, based on either the reciprocity theorem or bias field correction. Results show that insufficient spoiling yields systematic errors in absolute proton density of about 3-4 pu. A correction algorithm is proposed. It is shown that receiver coil sensitivity mapping based on the reciprocity theorem yields erroneous proton density values, whereas reliable data are obtained with bias field correction. Absolute proton density values in different brain areas, evaluated on six healthy subjects, are in excellent agreement with recent literature results.     

Proton MR spectroscopy of the lumbar spine in patients with glycogen storage disease type Ib.

Glycogen storage disease type Ib is an autosomal recessive inherited metabolic disorder resulting from deficiency of the microsomal glucose-6-phosphatase enzyme system. Six patients (three of which were treated with granulocyte colony stimulating factor) suffering from this disease were examined using image guided localized proton magnetic resonance (MR) spectroscopy. The relative signal intensities of water and lipid protons of the lumbar spine were determined. Comparison was made with iliac crest biopsies in the glycogen storage disease type Ib patients and localized proton MR spectroscopic values of the lumbar spine obtained by thirteen healthy volunteers. The data demonstrate for the first time that hypercellularity and myeloid hyperplasia in subjects with glycogen storage disease type Ib due to functionally impaired leucocytes results in a strongly increased water proton signal with a very low or absent lipid signal in localized proton MR spectroscopy. Upon granulocyte colony stimulating factor treatment, the water proton signal in the lumbar spine is not further augmented.     

Magnetic resonance imaging of the brain: Blood partition coefficient for water: Application to spin-tagging measurement of perfusion

We describe the use of relative proton density imaging to obtain spatially resolved measurements of the brain:blood partition coefficient for water. Values of relative proton density and apparent-T1 were calculated by performing a multidimensional nonlinear least squares fit of progressive saturation image data. Correction for magnetic field inhomogeneity was included. The partition coefficient was calculated by dividing the relative proton density of brain by the relative proton density of blood water. Results obtained from healthy volunteers demonstrate significant spatial variation in the partition coefficient in brain. Direct measurement of this parameter eliminates a source of error in the calculation of regional perfusion using arterial spin-tagging techniques.     

Subcortical gray matter N-acetylaspartate reduction in two cases of vascular dementia

Many of the previous studies of vascular dementia using proton magnetic resonance (MR) spectroscopy had been carried out on white matter. However, no proton spectroscopic data of the subcortical gray matter are available in such disease. We report two cases suffering from vascular dementia, with an unilateral N-acetylaspartate (NAA) decrease on subcortical gray matter. This significant reduction in NAA ratios was associated with an increase of choline on the ipsilateral centrum semiovale. We discuss the pathophysiology of these cases.