We developed a large-scale magnetically levitated electrode ionization chamber and examined a performance characteristic of the chamber with the volume of 8 liters. We confirmed that the ionization chamber can definitely measure low level radiation dose. We measured background dose under the condition that a device was put in an airtight container. We obtained the result that the opening of the chamber's shutter did not influence measurement of background. We measured also dose rate of background by the ionization chamber with the different volumes of 1, 8 and 14 liters simultaneously. Then, we obtained the same experimental results about magnitude and time fluctuation of the dose equivalent rate, even if ionization volumes were different. In measurement of 8 liters ionization chamber under time intervals 10, 30 and 60 minutes, a detection limit with reliability 68% were 0.0054, 0.0027 and 0.0012μSv/h, respectively.
Using electron spin resonance (ESR) spectroscopy, we revealed the thermal decay process of radicals induced in wheat flours by γ ray irradiation. Upon irradiation, a broad satellite signal was newly generated in the vicinity of the g==2.0 regions. By heating treatment, the satellite signals decreased exponentially. In order to evaluate the radical decay during heating, we defined a time-dependent master equation. Based upon the general solution of the equation, we evaluated the time constant of the radical decay through the nonlinear least squares method.
A method using BAS-MS type imaging plates (IPs) has been developed to estimate the values of ambient dose equivalent of scattered photon radiations in a diagnostic X-ray room where interventional cardiology procedures are frequently performed. An IP made of europium-doped BaFBr, a photostimulated luminescence material, is a highly sensitive two-dimensional radiation sensor. IP can be used as a passive dosemeter for a specific period, combined with a post-irradiation annealing procedure. The detector response to X-rays with effective energies between 30 and 120 keV were investigated via measurements with and without the use of metal filters (aluminum, copper, and cadmium) of varying thicknesses. The ambient dose equivalent can be evaluated by using a flat energy response to the dose equivalent obtained by taking the weighted sum of the sensitivity data measured under three different metal filters, without requiring knowledge of the effective energies of scattered photon radiations. The value of ambient dose equivalent at several measuring points in a diagnostic X-ray room was evaluated for periods of either 2 or 4 weeks using the flat ambient dose equivalent response and the annealing procedure. This method using IPs is practical for estimating values of ambient dose equivalent in a diagnostic X-ray room.