Tadashi Hashizume

Attenuation of 4-32 MeV X-rays in Ordinary Concrete, Heavy Concrete, Iron and Lead

Abstract The broad-beam attenuation coefficients for lead, iron, heavy concrete and ordinary concrete were evaluated using the X-ray beams from a 32 MeV betatron, a 31 MeV betatron and a 6 MeV linear accelerator for the purpose of the design of the protective shielding to be placed around high energy accelerators. Attenuations in these materials were determined by measuring the ionization in a cavity in a water phantom behind various thicknesses of materials. The variation in tenth-value thickness with field size for these materials is discussed on the basis of data obtained from the attenuation measurements. The tenth-value thickness for these materials is shown as a function of X-ray energy. The tenth-value thicknesses determined using the three X-ray generators are compared.

Spectra of primary x-ray and secondary photons from shielding materials for 4-30 MV x-rays

Abstract The spectra of primary X-rays and secondary photons from shielding materials (lead, iron, heavy concrete, ordinary concrete and water) have been studied experimentally over the megavoltage region 4–30 MV, using NaI(Tl) scintillation spectrometers, from the point of view of radiation protection against a medical betatron. Spectral measurements were made of both photons transmitted through and scattered from the shielding materials. The measured pulse-height distributions were converted to photon spectra, using inverse response matrices of the crystals. Resultant spectra are tabulated in the unit of the relative photon number per unit energy interval. The average energy of primary and secondary photons has been calculated from the spectrum. Spectra experimentally determined are compared with theoretically calculated spectra.

Genetically significant dose from beam therapy in Japan, 1971.

The genetically significant dose (GSD) from beam therapy in 1971 was estimated, based on a nationwide survey carried out for a 30 consecutive day period in June and July 1971. From 1480 hospitals which had therapy units, 348 hospitals were selected at random for the survey. Sixty-eight per cent of the questionnaires were answered. The contribution to the GSD from beam therapy in Japan was estimated by using the results of experiments on scattered and leakage radiation, designed to allow a reasonable projection of the dose; percentage depth dose tables; and determination of the expected number of children from vital statistics. The GSD estimated was 0.25, 0.70 and 0.03 mrad/person/yr for therapies with O0Co units, conventional X-ray units and high-energy accelerators, respectively.

ESTIMATION OF GENETICALLY SIGNIFICANT DOSE EQUIVALENT FROM OCCUPATIONAL EXPOSURE TO EXTERNAL SOURCES OF RADIATION IN JAPAN.

The genetically significant dose equivalent from occupational exposure in Japan has been estimated. The annual individual dose from external X-ray, gamma-ray and neutron sources in various types of radiation work has been evaluated from the personnel monitoring records. This report also presents information on the numbers of installations and radiation workers in Japan. The mean annual dose equivalent in medical, industrial, research and educational, and atomic work was 377,291, 88.6 and 125 mrem per yr, respectively. The genetically significant dose equivalent in medical, industrial, research and educational, and atomic energy work was 0.082, 0.032, 0.0053 and 0.0056 mrem per yr, respectively.