Beta-ray absorbed dose standard to tissue (I)

An absorbed dose standard to tissue at a depth of 7 mg/cm2 has been established for external beta radiations of 90Sr-90Y, 204Tl and 147Pm. This standard, which satisfies the recommendation of ISO 6980 (1984), is being used for the calibration of protection level dosemeters, doseratemeters and beta-ray sources. The standard is composed of a standard extrapolation chamber, a standard beta-ray irradiation system and a charge measurement system. The former two were designed and fabricated in our laboratory. The measuring method, the physical constants and the correction factors, which have been used for the dose evaluation, are described in this report. The absorbed dose rates at a calibration distance of 30 cm for 90Sr-90Y and 204Tl sources, and 20 cm for 147Pm source on Oct. 1992, are 11.5, 2.22 and 0.80 μ Gy/s, respectively. The total uncertainties of these values are 1.7% for 90Sr-90Y and 204Tl beta radiations, and 3.1% for 147Pm beta radiation.