Monte Carlo analysis of pion contribution to absorbed dose from Galactic cosmic rays

Accurate knowledge of the physics of interaction, particle production and transport is necessary to estimate the radiation damage to equipment used on spacecraft and the biological effects of space radiation. For long duration astronaut missions, both on the International Space Station and the planned manned missions to Moon and Mars, the shielding strategy must include a comprehensive knowledge of the secondary radiation environment. The distribution of absorbed dose and dose equivalent is a function of the type, energy and population of these secondary products. Galactic cosmic rays (GCR) comprised of protons and heavier nuclei have energies from a few MeV per nucleon to the ZeV region, with the spectra reaching flux maxima in the hundreds of MeV range. Therefore, the MeV-GeV region is most important for space radiation. Coincidentally, the pion production energy threshold is about 280 MeV. The question naturally arises as to how important these particles are with respect to space radiation problems. The space radiation transport code, HZETRN (High charge (Z) and Energy TRaNsport), currently used by NASA, performs neutron, proton and heavy ion transport explicitly, but it does not take into account the production and transport of mesons, photons and leptons. In this paper, we present results from the Monte Carlo code MCNPX (Monte Carlo N-Particle eXtended), showing the effect of leptons and mesons when they are produced and transported in a GCR environment.     

空间辐射剂量学浅谈

空间辐射剂量学是辐射防护领域最具挑战性的学科之一。本文着重介绍：(1)低地球轨道空间辐射的主要来源：银河系宇宙射线,地球磁场捕获的高能电子和质子形成的地球辐射带．太阳粒子事件以及宇宙射线与地球大气相互作用产生的反照中子和质子;(2)各种辐射成分对剂量的贡献;(3)空间辐射剂量的测量方法。主要介绍有源探测器和无源探测器,它们的使用范围以及各自的优缺点。同时,简要介绍了国外目前使用的主要探测器及其特点,并对国际剂量学的发展历史作了简单的回顾。     

ALTEA: The instrument calibration

The ALTEA program is an international and multi-disciplinary project aimed at studying particle radiation in space environment and its effects on astronauts’ brain functions, as the anomalous perception of light flashes first reported during Apollo missions.The ALTEA space facility includes a 6-silicon telescopes particle detector, and is onboard the International Space Station (ISS) since July 2006.In this paper, the detector calibration at the heavy-ion synchrotron SIS18 at GSI Darmstadt will be presented and compared to the Geant 3 Monte Carlo simulation. Finally, the results of a neural network analysis that was used for ion discrimination on fragmentation data will also be presented.     

航天器发射事故中钚-238热源辐射风险评估模型的建立及应用

辐射风险是航天器使用钚-238热源的关键问题。本文以“嫦娥三号”任务为例,提出钚-238热源在航天器应用过程中的辐射风险评估内容和方法,建立相应的风险评价模型。评估结果显示,使用钚-238热源的辐射风险较低。本文建立的分析方法可为使用核能源的航天任务辐射风险评估提供参考。     

Dosimetry during Space Missions

The United States' astronauts have been exposed to a complex radiation environment that poses unique problems in high-energy radiation dosimetry. Since the astronauts were exposed to natural radiation sources with a potential for delivering very large radiation exposures, exposure limits in excess of occupational limits were adopted. These limits represent a balancing of the risk from injury due to radiation exposure against other very high risks inherent in space flight and against the benefits to be derived from the space missions. The limits adopted for Apollo, Skylab, and Apollo/Soyuz are given along with the details of the radiation monitoring activities of the mission. The radiation exposures experienced in the United States' space missions are also given.     

Calibration factors for the SNOOPY - NP-100 neutron dosimeter

Within CANDU nuclear power facilities, only a small fraction of workers are exposed to neutron radiation. For these individuals, roughly 4.5% of the total radiation equivalent dose is the result of exposure to neutrons. When this figure is considered across all workers receiving external exposure of any kind, only 0.25% of the total radiation equivalent dose is the result of exposure to neutrons. At many facilities, the NP-100 neutron dosimeter, manufactured by Canberra Industries Incorporated, is employed in both direct and indirect dosimetry methods. Also known as “SNOOPY”, these detectors undergo calibration, which results in a calibration factor relating the neutron count rate to the ambient dose equivalent rate, using a standard Am-Be neutron source. Using measurements presented in a technical note, readings from the dosimeter for six different neutron fields in six source-detector orientations were used, to determine a calibration factor for each of these sources. The calibration factor depends on the neutron energy spectrum and the radiation weighting factor to link neutron fluence to equivalent dose. Although the neutron energy spectra measured in the CANDU workplace are quite different than that of the Am-Be calibration source, the calibration factor remains constant - within acceptable limits - regardless of the neutron source used in the calibration; for the specified calibration orientation and current radiation weighting factors. However, changing the value of the radiation weighting factors would result in changes to the calibration factor. In the event of changes to the radiation weighting factors, it will be necessary to assess whether a change to the calibration process or resulting calibration factor is warranted.     

热释光测量法在空间辐射剂量学中的应用

空间电离辐射是带电粒子辐射,为了保障人类航天活动的辐射安全,空间辐射剂量学得到了很大的发展。热释光测量法已被证明是空间辐射剂量不研究的优选方法之一,它广泛应用于国内外航天器舱内累积剂量的测量。其中,氟化锂已成为必用的热释光探测器。研究其质子响应特性的发光量与空间剂量的关系是将氟化锂应用于空间要作的重要工作。本文介绍了国外应用情况和自己的工作。     

Development and evaluation of the Combined Ion and Neutron Spectrometer (CINS)

The Combined Ion and Neutron Spectrometer, CINS, is designed to measure the charged and neutral particles that contribute to the radiation dose and dose equivalent received by humans in spaceflight. As the depth of shielding increases, either onboard a spacecraft or in a surface habitat, the relative contribution of neutrons increases significantly, so that obtaining accurate neutron spectra becomes a critical part of any dosimetric measurements. The spectrometer system consists of high- and medium-energy neutron detectors along with a charged-particle detector telescope based on a standard silicon stack concept. The present version of the design is intended for ground-based use at particle accelerators; future iterations of the design can easily be streamlined to reduce volume, mass, and power consumption to create an instrument package suitable for spaceflight. The detector components have been tested separately using high-energy heavy ion beams at the NASA Space Radiation Laboratory at the Brookhaven National Laboratory and neutron beams at the Radiological Research Accelerator Facility operated by Columbia University. Here, we review the progress made in fabricating the hardware, report the results of several test runs, and discuss the remaining steps necessary to combine the separate components into an integrated system. A custom data acquisition system built for CINS is described in an accompanying article.     

用于中子剂量当量仪校准的同位素中子参考辐射的建立

建立了三种辐射中子源项的同位素中子参考辐射场,对有关技术内容和方法以及达到的技术指标进行了总结;介绍了参考辐射场的标准化中子参数及其测量方法。结果表明,已建立的同位素中子参考辐射满足有关技术规范要求,可用于中子剂量当量仪的校准和检定。     

Studies of the radiation environment on the Mars surface using the Geant4 toolkit

The radiation environment on the surface of Mars is a potential threat for future manned exploration missions to this planet.In this study,a simple geometrical model was built for simulating the radiation environment on the Mars surface caused by galactic cosmic rays;the model was built and studied using the Geant4 toolkit.The simulation results were compared with the data reported by a radiation assessment detector （RAD）.The simulated spectra of neutrons,photons,protons,a particles,and particle...     

TEPC中子和γ分辨技术研究

混合辐射场中子剂量、剂量当量的测量需进行中子、γ分辨。依据各种辐射沉积线能的不同,组织等效正比计数器（TEPC）具有一定的中子、γ分辨能力。本文采用自制的圆柱形TEPC在5SDH-2加速器单能中子辐射场进行了微剂量谱测量,对其中子、γ分辨技术进行了探讨分析。采用¹³⁷Cs纯γ辐射微剂量谱匹配法,在²⁵²Cf、²⁴¹Am-Be中子辐射场进行了中子、γ分辨研究。分辨后的中子剂量当量与约定真值一致性较好,表明TEPC用于中子、γ混合辐射场的吸收剂量、剂量当量测量是可行的。     

Synthesis and Characterization of a Soft-tissue Substitute for Neutron Dosimetry

To develop a physical phantom for neutron dosimetry, a solid soft-tissue substitute was synthesized. The synthesized tissue substitute, NAN-JAERI, is improved in both hydrogen and oxygen elemental composition in comparison with existing tissue substitutes. To examine the radiation characteristics of the new soft-tissue substitute, absorbed dose distributions in NAN-JAERI were measured using a ²⁵²Cf neutron source. The measured absorbed dose distributions of neutrons and photons agree with those calculated by a Monte Carlo simulation code MCNP. The agreement between the experiment and the simulation verifies this method of evaluating the soft-tissue equivalence of NAN-JAERI for ²⁵²Cf neutrons. Similar simulations for some mono-energetic neutron sources showed that the newly developed tissue substitute has soft-tissue equivalent characteristics in the neutron energy range from 1 MeV up to 14 MeV, in terms of the absorbed dose distributions in a slab phantom.     

Design characteristics and fabrication of radioisotope heat sources for space missions

Radioisotope thermoelectric generators (RTGs) have been used by the United States to provide electrical power for spacecraft since 1961. All RTGs that have been launched by the U.S. have used heat sources fueled with the plutonium-238 isotope. Low-power (1 W_thermal) Light Weight Radioisotope Heater Units have also been used to maintain spacecraft equipment within their normal operating temperature range. Los Alamos National Laboratory is responsible for fabricating heat sources for current and future space missions. The ²³⁸PuO₂ is purified by aqueous processing, fabricated into hot pressed pellets, encapsulated into precious metal cladding material, then the fueled clads are nondestructively tested. NASA currently plans for the potential use of radioisotope power systems for the Europa Orbiter and the Solar Probe missions, which are all scheduled for launch this decade. In addition several Mars Exploration missions over the next decade will employ radioisotope heater units.     

高灵敏中子剂量当量率仪的能量和剂量响应校准

参考国内标准化和国际标准化组织（ISO）及国际电工委员会（IEC）对中子（率）仪校准的相应标准,对已设计、加工、组装完毕的1台长圆柱状、较大体积、高灵敏中子剂量当量率仪,在宽能区（热中子～20MeV）内进行了能量响应和剂量灵敏度的实验校准。本文介绍了仪器能谱响应函数曲线实验校准方法、实验方案和结果分析,给出了仪器的综合灵敏度48.9s－1/（µSv•h－1）及在3种特征能谱中的剂量响应。     

High-energy neutron-radiation reference field

The technique and results of measurements performed of the neutron spectrum behind the top shielding of the U-70 experimental hall using a Bonner spectrometer based on indium and carbon activation detectors are presented. The integral characteristics of the neutron field are presented; such a field could be useful in various areas of dosimetry, radiation physics, and radiobiology, in assuring radiological safety during flights in airplanes and in space, as well as in the study of malfunctions induced in microelectronics by high-energy neutrons.     

Optimization of the radiation shielding mass for the magnet coils of the VISTA spacecraft

An attempt has been made for the optimisation of the radiation shielding of a spacecraft design concept with inertial fusion energy propulsion for manned or heavy cargo deep space missions beyond earth orbit. Rocket propulsion is provided by fusion power deposited in the inertial confined fuel pellet debris, and with the help of a magnetic nozzle. The allowable nuclear heating in the super conducting magnet coils (up to 5 mW/cm³) is the crucial criterion for the dimensioning of the radiation shielding structure of the spacecraft. The optimized design reduced the shield mass from 600 tons to 93 and 88 tons with natural and enriched lithium, respectively. The space craft mass was 6000 tons. Total peak nuclear power density in the coils is calculated to be 5.0 mW/cm³ for a fusion power of 17,500 MW. Peak neutron heating density is 2.6 mW/cm³ and peak γ-ray heating density is 2.9 mW/cm³ (all on different points). However, volume averaged heat generation in the coils is much lower, namely 0.30, 0.73 and 1.03 mW/cm³ for neutron, γ-ray and total nuclear heating, respectively.     

空间用238pu放射源辐射影响分析

我国在某航天任务中,将首次应用238Pu放射源.本文从该放射源所用的原料、放射源的结构、产生的射线种类以及包壳活化等方面分析了238Pu放射源在航天应用过程中的辐射特性.通过分析实验表明,距单个放射源1m处的中子辐射剂量率约为60 u Sv·h-1,在采取适当措施后,238Pu放射源将不会对人员和环境产生明显的辐射影响.     

The Simulation of Space Radiation Damage to Spacecraft Systems

Space radiation has induced damage to spacecraft in near earth orbits in a number of documented cases. Explorer XIV, Explorer XV, UK-1, TRAAC, TRANSIT IV B and TELSTAR I were among these. It has become imperative that an adequate laboratory simulation technique be found and applied to future spacecraft to extend the useful lifetime of spacecraft and prevent premature failures. The choice of the equipment for carrying out laboratory simulations at Goddard Space Flight Center has been made by an analysis of damage produced in semiconductor devices. The relative damage produced in semiconductors with various particle energies was compared with the number of those particles at each energy in space to produce a curve showing the particle energies which are most damaging in space. From the curves it becomes clear that energies from about 1 to 4 Mev are the most damaging for electrons and protons. Therefore, the Goddard Space Flight Center will have a facility with a 0.5-3 Mev electron accelerator, a 0.5-4 Mev proton accelerator and a 0.1-1 Mev proton-electron accelerator, to cover the low energy range. The facility will also have a 30,000 curie Cobalt 60 area able to irradiate whole spacecraft to simulate ionization damage effects. With these facilities a reasonable program of radiation hardening of long-lived spacecraft may be carried out.