Undyed and dyed polymethylmethacrylate dosimeters are widely used as routine dosimeters in radiation processing for the absorbed dose range 5-50 kGy, especially in the radiation sterilization of disposable medical products. Basic characteristics ofRadix RN15 ; a commercially available undyed polymethylmethacrylate dosimeter, was studied also in the dose range 1-10 kGy, for its wide application to radiation processing especially for the evaluation to decide sterilization dose and the quality assurance of food irradiation. The characteristics of dose response, the effect of irradiation temperature, and its stability after irradiation were examined at readout wavelength 270-320 nm. The dose response read-out at shorter wavelength is higher than that at longer wavelength. The measurable dose range of 1-10kGy is obtained at the readout wavelength of 280 nm that is shorter than conventional read-out wavelength of 320 nm. The postirradiation stability of dose response for 6 kGy is less than 4-5% for longer than 24h after irradiation. The dose response slope at 6 kGy while held at irradiation temperatures in the range -40-40°C, increases with temperature up to 20°C as the maximum, and decreases at higher temperatures. Radix RN15 has linear temperature dependence with a coefficient of +0.25%/°C, relative to the dose response at under 20°C, at irradiation temperature in the range -40-20°C.
Accelerator mass spectrometry (AMS) was applied to measurement of 129I/ 127I ratio to determine 129I concentration in radioactive waste. Solid phase extraction disks (Anion-SR) for chemical separation of iodine from radioactive waste samples were used to prepare AMS targets.This method made it possible to swiftly separate iodide ions from sample solutions, compared with a conventional liquid-liquid extraction method. Since the129I concentration is calculated from an129I/127I ratio, the amount of an 127I carrier added to a sample for chemical separation determines the measurable range of the129I concentration. Especially in a radiation controlled area, it is important to keep the background value of the129I/127I ratio as low as possible. The present method was successfully applied to laboratory standards and liquid waste samples arising from nuclear facilities in Japan Atomic Energy Agency.
The timescale of magmatic processes of Izu arc volcanoes, Japan, was estimated by the238U - 230Th disequilibria in the volcanic products from the volcanoes. The majority of the 230Th/238U activity ratios of the products were less than unity, being enriched in238U relative to230Th. The (230Th/232Th) - (238U/232Th) diagram for younger Fuji and Izu-Oshima volcanoes formed a whole rock isochrons, and the ages were l×104 and 2×104 years, respectively. The (230Th/232Th) - (238U/232Th) data set for younger Fuji volcano formed a cluster on the diagram, while those of Izu-Oshima formed another cluster apparently apart from each other, suggesting that the concentration of U and Th may possibly be un-uniform in the mantle beneath Izu arc.
The activity ratios of228Ra/226Ra in the leachates from a granite sample with HCl, NaOH and NaCl aqueous solutions were observed to be smaller than that in the granite sample. The activity ratios of224Ra/228Ra, 230Th/232Thand228Th/232Thincreased with an increase in pH of the HClaqueous solution. The leaching behavior of226Raand224Ra which are formed through 5 decay processes of 238Uand through 4 decay processes of232Th, respectively, was different from that of228Rawhich is formed by a single decay of232Th. Thorium isotopes, 230Th and228Th, decay products of238U and232Th, respectively, were also leached more effectively than 232Th.The leaching efficiency of Ra and Thisotopes was estimated to be dependent on the difference in the history of decay processes which have formed the nuclides. This estimation was consistent with the observations with the radioactive mineral samples reported previously.