Testing and calibration of radiation dosimeters designed for astronauts during an EVA

An active real-time dosimeter will be required for astronauts during extra vehicular activities (EVA). It must be capable of measuring and recording the dose rate and quality factor from galactic cosmic rays during ambient conditions. It must also record the dose and issue a warning to the astronaut during the initiation of a high intensity solar particle event (SPE). This dosimeter can be integrated into the new space suit configuration that is currently under design by National Aeronautics and Space Administration (NASA) or installed in a transportation rover or tool box. The National Space Biomedical Research Institute (NSBRI) is the administrative agency for this EVA initiative. The mission of NSBRI is to support NASA in understanding health concerns for astronauts during long term missions in space. It is a nonprofit agency dedicated to promoting research and dissemination of results through publications and scientific meetings. General specifications outlined by NASA are that the detectors should be tissue equivalent, omni-directional and capable of measuring ambient dose rates of 300 μGy/d for particles with LET ranging from 0.2 to 300 keV/μm. At the onset of a solar particle event the system must be capable of signaling an alarm at 0.05 mGy/min and at 10 mGy/min. Simultaneous measurements of the dose to the skin (surface) and blood forming organs (1 cm depth) must have a time resolution of 1 minute and a latency period less than 5 minutes. A Tissue Equivalent Proportional Counter (TEPC) gives details of the absorbed dose and dose rate. It can also provide direct information on the quality or type of the radiation field. The interior cavity of the detector is filled with tissue equivalent gas such that the density thickness, cm²/g, of the gas is equivalent to the density thickness of tissue with dimensions approaching the nucleus of a mammalian cell (1-5 μm). The motivation for this was that the proportional counter serves as a microdosimeter that can detect energy deposition events similar to those encountered by biological systems having the similar dimensions. The objectives of the experiments at HIMAC are to measure the response of the dosimeters to HZE particles and evaluate the how this response changes with incident particles. (author)