The transmission factor of annihilation γA rays (511 ke V) for radiation shielding materials has been estimated by means of the Monte Carlo simulation based on three kinds of geometries of (1) a point isotropic source in infinite thick material, (2) a point isotropic source in finite thick material and (3) vertical incident to finite thick material. The present results show that the factor for geometry (1) is the largest, that for geometry (2) is next and that of the geometry (3) is the lowest. We have also found the cases in which the factor for geometry (1) is 2-3 times larger than the factors for geometries (2) and (3). The transmission factors for main γA-ray emitting nuclides, given in “Manual of Practical Shield Calculation of Radiation Facilities (2000)”, are available only for the geometry (1). The present work indicates that the use of these values the calculation for actual shield geometries often causes the overestimate of effective doses. The transmission factor data for the geometries (2) and (3) are clearly necessary for more reliable shield calculations.
The external exposure dose to the radiation worker and the temporary entrant is monitored with a personal dosimeter. Semiconductor-type electronic pocket dosimeters (EPDs), Aloka PDM-102, have been used at the Radioisotope Research Center of Osaka University since 1991.Performance tests of the EPDs were repeatedly undertaken by using the gamma-ray irradiation system which is usable for the calibration of personal dosimeters and survey meters and for low-dose irradiation of experimental animals.The EPDs were set on JIS P-1 phantom to investigate the dose rate response, secular change and angular response.It was confirmed that the indicated value agreed within 1% when EPD was irradiated with a fixed dose equivalent of 42.0 μ Sv at three different dose rates, 242, 168 and 108 μ, Sv/h.Calibration factors obtained in the secular change test were in a range from 1.00 to 1.14.It is concluded that the EPDs are sufficiently acceptable for practical applications.It should be noted that in the angular response test the indicated value from the back side was found about 15% lower than that from the front side.
Radiation safety training course has been started on March, 2001 by Radioisotope Research Center, University of Tokushima. And the RI Center has also given re-training course for three years from 2001 to 2003. In the recent courses, a radiation worker's knowledge and recognition about Radiation Safety Handling was investigated, relating with the attendance frequency of those courses.It was found that the basic radiation safety behavior such as putting on monitoring badge, lab coat still was not understood for some persons. On the other hand, the RI center's radiation safety training course gave a correct knowledge and recognition on the radiation safety for most of radiation workers. Furthermore, the times of the attendance improved about that recognition.
Laws concerning radiation safety management were analyzed from the point of view of defining precisely what is meant by radiation and what is meant by the subject. There are no laws to protect students from radiation hazards when using X-rays and electron beams under 1 Me V for research and/or education. The Law concerning Technical Standards for Preventing Radiation Hazards gives the authorities the power to enact new rules and regulations that will protect the students. The Radiation Council must take charge for enactment of all laws regarding radiation safety management.