To establish a systematic guideline for accelerator decommissioning, as a case study, beamline activation of 12 MeV-proton electrostatic accelerator was investigated employing a survey meter and γ-ray spectrometers. Beam loss points where reflected as high dose-rate area were identified, and generated nuclides and their activities were determined. Almost beamline components are made from stainless steel and 52Mn and 56Co were detected as principal induced activities. It was found that the 56Co activity significantly contribute to the dose rate value denoted on the survey meter. From the beam operation history and the monitor currents of Faraday-cups, we revealed the beam loss on a certain point significantly reflects the 52Mn activity on there. Induced activities of 52Mn and 56Co on the certain point of the beamline could be reproduced by the contact dose-rate on that point.
In this study, the application of a simple measurement method using NaI(Tl) scintillation survey-meter to detect the gamma-rays in the armor tiles of LHD vacuum vessel exposed to fast neutrons during deuterium plasma experiments was evaluated to control the occupational exposure for the storage of huge numbers of the armor tiles. The gamma-ray spectrometry for an activated armor tile by high-purity germanium detector (HPGe) showed the gamma-ray peaks from 58Co, 54Mn and 60Co. The detection efficiencies of these nuclides for HPGe were evaluated by PHITS to estimate the concentrations of these nuclides. The radiation transport model for HPGe in PHITS were validated by the gamma-ray measurements for sealed gamma-ray sources. Then, the detection efficiencies of these nuclides for NaI(Tl) scintillation survey-meter were also evaluated by the same manner using PHITS. The predicted dose rate of the activated armor tiles in NaI(Tl) scintillation survey-meter was consistent with the actual measurement. The predicted count rate in NaI(Tl) scintillation survey-meter for 60Co, which will be a deterministic nuclide in the armor tile due to longer half-life, in the clearance level was sufficiently higher than the minimum detectable count rate of NaI(Tl) scintillation survey-meter with a simple shielding for environmental radiation.
The dispersions of short-lived radionuclides emitting α-particles, such as 223Ra, 211At, and 225Ac, during animal experiments were measured for radiation safety management. These three radionuclides dispersed from mice were trapped using charcoal-impregnated filters, and those in feces were collected directly, and those in urine were recovered with bedding in a breeding cage. For all the radionuclides, uptakes by tissues were also further examined after dissection. The radioactivity of each radionuclide was evaluated with a γ-ray scintillation counter using daughter nuclide. In tumor bearing mice, 211At and 223Ra accumulated in tumor tissues with high affinity and less accumulated in other tissues. It was noted that all the three radionuclides were not exhausted or evaporated from the breeding cages and the peak of excretions of the radionuclides in the animal experiments was observed within twenty-four hours.
Various materials containing the natural radioisotope potassium-40 (40K) are often used for radiation education, but their radioactivity is not usually known. In the present study, low-sodium salts (LS salts) were purchased at several shopping malls in Japan, and the radioactivity of 40K in the LS salts were calculated from the nutritional tables and cutting down rates (CDR) printed on their packages. CDR is the percentage of sodium chloride (NaCl) in common salts replaced with potassium chloride (KCl). Solid disks were fabricated from the LS salts and KCl reagent, and their radiation count rates (cps/g) were measured by GM survey meter and CsI spectrometer. In these measurements, the KCl disk was used to determine the conversion factors (Bq/cps) for determining radioactivity of 40K in the LS salts. It was found that the experimentally obtained radioactivity generally coincides with that calculated from the nutritional tables, but it does not always coincide with that calculated from CDR.