Japanese Experiment Module (Kibo) had been build into the International Space Station (ISS), which is a multipurpose manned facility and laboratory and is operated in orbit at about 400 km in altitude. Two Japanese astronauts stayed in the ISS for long time (4.5 and 5.5 months) for the first time. Space radiation exposure is one of the biggest safety issues for astronauts to stay for such a long duration in space. This special paper is presenting commentary on space radiation environment in ISS, neutrons measurements and light particles (protons and electrons) measurements, the instruments, radiation exposure management for Japanese astronauts and some comments in view of health physics.
Radiation use in medicine generally gives us the benefit that outweighs the risk. However, some patients are much concerned about the risk while some medical people are unaware of radiation risk. The aim of this report is to review the low dose risk not only in the reports of ICRP, UNSCEAR, BEIR and French academy but also in the scientific papers that have been paid attention to. On these bases, we discuss the low dose risk and how we face the risk in medicine in order to go for medical use of radiation to the right way. In particular, we hope this report will support medical people as well as radiation protection experts should understand the radiation risk in medicine on current scientific basis.
The removal factor in the smear method was measured experimentally for materials that are used in transport casks for spent fuel, storage casks and ships for transporting them. We used 60Co for fabricating contaminated tested materials, because 60Co is the key radioactive nuclide contaminant at nuclear power stations. For the tested metallic materials, the removal factors obtained experimentally ranged from 0.7 to 0.8. The removal factors obtained experimentally were 0.4 for the surface of a transport stand and hatch, 0.5 for the surface of the upper deck and 0.3 for the surface of the storage cask. These values can be used to survey radioactive surface contamination. The removal factor was measured with varying pH of a radioactive standardized solution. The removal factor of SUS304 buff polishing (#300) did not change even when the pH of the radioactive standardized solution was changed. For painted materials, there was the tendency that the higher the pH of the radioactive standardized solution, the smaller the removal factor. However, at a pH greater than 3, the removal factor reached a saturation point. It is concluded that pH of the radioactive standardized solution is ineffective for determining the removal factor when the pH exceeds 3. The removal factor was also measured with varying direction of wiping the surface of the tested materials treated by mechanical cutting. No differences among the cases of the various directions of wiping the surface of the tested materials were observed.
Common salt (NaCl) has previously been suggested for use in dose estimation in accident dosimetry. In this study, we investigated the optically stimulated luminescence (OSL) and violet thermoluminescence (VTL) characteristics of “Aji-Shio” (Ajinomoto), a Japanese commercial salt. A comparison of OSL and TL signals allowed identification of common source traps. The initial OSL signal contained a dominant thermally unstable component, which necessitated prior heat treatment. Based on these luminescence characteristics, a single-aliquot regenerative-dose (SAR) OSL protocol was modified and tested. The protocol worked very well for six types of salt, but not for four other types of salt. A minimum detection limit of -15 mGy was estimated using the OSL protocol; this is lower than the value obtained from other forms of OSL retrospective dosimetry and lower than that obtained using electron spin resonance (ESR) dosimetry. It was concluded that the OSL from Japanese commercial salt could be used successfully to derive precise estimates of accident dose.
Individual external doses of inhabitants were examined in high levels of natural radiation areas (HLNRAs) in Ramsar. Each of 15 inhabitants in HLNRAs and 10 inhabitants in a control area carried an electronic personal dosimeter (EPD) for one day in April and in December 2005. In addition, their individual doses were estimated from indoor and outdoor radiation dose rates determined with a NaI (Tl) survey meter. A good correlation existed between the dose rate values obtained through estimation and personal measurement, and estimated annual doses ranged from 0.5 to 32 mGy/y. Each of the dosimetric subjects carried also an optically stimulated luminescence dosimeter (OSLD) for about one month in September 2005, but a few values obtained by these measurements deviated widely from those obtained by one-day measurements with EPDs and those estimated by environmental dosimetry. This deviation might have been due to the fact that these OSLDs were left behind somewhere in houses. Hence, the observed dose values depended heavily on the place where dosimeters had been left, because of the non-uniform distribution of Ra-226 contained in building materials as well as the structure of the house and the existence of shields.
The external exposure control systems in KEK and CERN are discussed to find out good practices and unreasonableness of radiation control in accelerator facilities, which plays an important role in optimizing national and/or site specific radiological regulations, referring to relevant ICRP publications. Personal dose limits and radiation area classifications were analyzed and their reasonableness were explored. Good example of supervised areas, area classification based on realistic assumptions on working time .etc are found. On the other hand, unreasonable systems, that are often attributed to the national regulation or ideas presented in the old publications are also found.