Space radiation hazards are recognized as a key concern for human space flight. For long-term interplanetary missions, they constitute a potentially limiting factor since current protection limits for low-Earth orbit missions may be approached or even exceeded. In such a situation, an accurate risk assessment requires knowledge of equivalent doses in critical radiosensitive organs rather than only skin doses or ambient doses from area monitoring. To achieve this, the MATROSHKA experiment uses a human phantom torso equipped with dedicated detector systems. We measured for the first time the doses from the diverse components of ionizing space radiation at the surface and at different locations inside the phantom positioned outside the International Space Station, thereby simulating an extravehicular activity of an astronaut. The relationships between the skin and organ absorbed doses obtained in such an exposure show a steep gradient between the doses in the uppermost layer of the skin and the deep organs with a ratio close to 20. This decrease due to the body self-shielding and a concomitant increase of the radiation quality factor by 1.7 highlight the complexities of an adequate dosimetry of space radiation. The depth-dose distributions established by MATROSHKA serve as benchmarks for space radiation models and radiation transport calculations that are needed for mission planning.
A commercial retarding field analyzer is used to measure the time-averaged ion energy distributions of impacting ions at the powered electrode in a 13.56 MHz driven, capacitively coupled, parallel plate discharge operated at low pressure. The study is carried out in argon discharges at 10 mTorr where the sheaths are assumed to be collisionless. The analyzer is mounted flush with the powered electrode surface where the impacting ion and electron energy distributions are measured for a range of discharge powers. A circuit model of the discharge, in combination with analytical solutions for the ion energy distribution in radio-frequency sheaths, is used to calculate other important plasma parameters from the measured energy distributions. Radio-frequency compensated Langmuir probe measurements provide a comparison with the retarding field analyzer data. The time-resolved capability of the retarding field analyzer is also demonstrated in a separate pulsed dc magnetron reactor. The analyzer is mounted on the floating substrate holder and ion energy distributions of the impinging ions on a growing film, with 100 ns time resolution, are measured through a pulse period of applied magnetron power, which are crucial for the control of the microstructure and properties of the deposited films.
The laboratory of Microbiology at SCK.CEN, in collaboration with different universities, participates in several ESA programmes with bacterial experiments that are carried out in the International Space Station (ISS). The main objective of these programmes is to study the effects of space flight conditions such as microgravity and cosmic radiation on the general behaviour of model bacteria. To measure the radiation doses received by the bacteria, different detectors accompanied the microbiological experiments. The results obtained during two space flight missions are discussed. This dosimetry experiment was a collaboration between different institutes so that the doses could be estimated by different techniques. For measurement of the high linear energy transfer (LET) doses (>10 keV microm(-1)), two types of etched track detectors were used. The low LET part of the spectrum was measured by three types of thermoluminescent detectors ((7)LiF:Mg,Ti; (7)LiF:Mg,Cu,P; Al(2)O(3):C) and by the optically stimulated luminescence technique using Al(2)O(3):C detectors.
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