1987 年 22 巻 1 号 p. 31-38
β-ray irradiation fields for calibrating radiation protection instruments, such as survey meters and personnel dosimeters, have been established.
The β-ray irradiation fields are formed with two types of plane sources; one is a thin ion exchange membrane source 100mm in diameter, and the other is an extended area source which has 42mm active diameter and is covered with silver foil. The radionuclides are 147Pm, 204Tl, 90Sr-90Y and 106Ru-106Rh.
The β-ray irradiation fields are characterized by their β-ray absorbed dose rates and residual maximum energies. Absorbed dose rates were measured with an extrapolation chamber (the entrance window thickness is 6.37mg/cm2) for every source and obtained as a function of irradiation distance. Residual maximum energies were determined by the absorption method. The residual maximum energy which is larger than the standard minimum value recommended by ISO (International Organization for Standardization) was obtained for every source.
The uniformity of the β-ray irradiation field was examined using large area industrial X-ray film. The examination indicated that the β-ray irradiation field was quite uniform and suitable for calibrating radiation protection instruments.
