The dose assessment of radiation workers from external exposure is principally carried out with the aid of personal monitoring device such as film badges or thermoluminescent dosimeters. This paper describes the present status of occupational exposures in Japan on the basis of the data concerning the individual annual cumulative dose equivalent by sex, age-group and type of radiation work which were obtained from a nationwide survey on the occupational exposure in 1978. According to the 1977 report of the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) and the Recommendations of the International Commission on Radiological Protection (ICRP), the collective dose equivalent, the special factor of dose distribution, Ω, and the index of harm for radiation-induced somatic and genetic effects were calculated from the cumulative dose equivalents determined with the personal monitoring devices. In spite of increasing in the number of radiation workers who must be monitored for neutron exposure, the collective dose equivalent of neutrons was negligibly small compared with the X and gamma-ray dose equivalent. In Japan, the NTA film badges are commonly used as the personnel neutron dosimeters for radiation-protection purposes. The problem of personnel neutron monitoring is discussed in this paper, together with the determination of quality factor. Also, this paper reviews a few problems in the determination of the effective dose equivalent and dose equivalent index.
A one-dimensional Monte Carlo transport code for the propagation of gamma radiation in two medium geometry is developed to evaluate properties of the radiation field due to the washout of short-lived radon daughters from the atmosphere to the ground surface by precipitation. To assess the validity of the results provided by this code, the calculations on the radiation field from uniformly distributed terrestrial 238U source in the natural environment are compared with numerical calculations of other investigators. The comparison shows satisfactory agreement between them. The calculated data are presented on the height distribution and on the energy and angular distribution of flux density and exposure rate from an infinite plane isotropic RaB and RaC sources with known abundances on the ground-air interface.
A method of dehydration for the waste treatment of radioactive animal carcass by microwave heating was developed. A heating apparatus was devised by annexing the microwave output controlling circuit to a 600W commercial microwave oven, and the aqueous vapour from the animal carcass was collected by duplex cold traps. Body weight of the carcass was reduced to 20-30% by dehydration, and a three-year storage test proved that the dehydrated carcass was very hard to decompose. Time needed for dehydration was about 10min for a 25g mouse, and about 1hr for 668g dog. Violent rupture of the carcass, and/or fuming due to overheating that had often been observed during dehydration were proved to be avoidable by controlling the microwave output during the process. The ratio of radioactivity (60Co, 137Cs, 85Sr, 144Ce) that escaped from the carcass during dehydration was found to be less than 3×10-4 by a series of experiment. Some related radiation safety problems were discussed.
The principal co-precipitation mechanism of radioactive strontium with barium sulfate is the isomorphous replacement between Ba2+ and Sr2+ in the crystal. Thus, the removal ratio of radioactive strontium from an aqueous solution depends on the equilibrium constant, solubility product and quantities of barium sulfate, and SO42- concentration. In low salt concentration, the equilibrium constant, K, for barium sulfate which was prepared with the reaction of Ba2+ and SO42- in the test solution was 1.9×10-4. On the other hand, the equilibrium constant for powdered barium sulfate added was Ks=9.1×10-6. In a high salt concentration less than about 3×10-1mol/l NaCl and NaNO3, and less than about 1.0mol/l Na2SO4, the experimental removal ratio agrees with the calculated values. But in high salt concentrations ranging from 3×10-3mol/l to the saturated concentration of NaCl and NaNO3, ranging from 1.0mol/l to the saturated concentration of Na2SO4, the experimental removal ratio decreases.
Ionization efficiency of a spherical ionization chamber with a volume of 1.26 liters for the determination of radioactivity concentration of tritium-protium gas was calculated by Monte Carlo method. The calculated value of the ionization efficiency agreed with the experimental one determined by a method in which tritium-protium gas was converted to tritiated water by low-pressure explosion method and the radioactivity of the tritiated water was measured by a liquid scintillation counter calibrated with a reference source.
222Rn escape-to-production ratio of soil is estimated based on the 226Ra concentration determined by using NaI(Tl) detector and the 222Rn emanating power of soil (the 222Rn emanating power of soil is the activity of 222Rn that escapes into soil gas per gram of dry soil at equilibrium state). The value for it is 32.2±5.9% for the soil of the campus of Nagoya University. The dependence of 222Rn escape-to-production ratio of this soil on the water content of soil is observed. The measurement of the 222Rn escape-to-production ratio is also carried out by using Ge(Li) detector. In measuring the sampled soils, they are not dried because of the dependence of 222Rn escape-to-production ratio of the soil on the water content of soil. The measured value for the soil of the campus of Nagoya University is 38.9±5.0% and agrees with that measured by the above-mentioned technique. In contrast to the method hitherto used, the method presented in this work enables us to evaluate exposure rate from the sources of 238U-series precisely and easily in a laboratory.