With increasing the uses of atomic energy and ionizations, the increasing human exposures from man-made radiations have aggravated the possibility of the occational induction of malignant diseases in the exposed population. In order to aid in developing a better understanding of the mechanism of radiation damage and to guide in the establishment of safe levels of exposure to ionizing radiations, it is importance to know the human exposure on a population scale as well as an individual exposure. Up to date, some data on the human exposure are available from medical exposure, occupational exposures, environmental contamination from weapon fallout, nuclear weapon exposures at Hiroshima and Nagasaki, radiation accidents, and other sources such as exposures in high-flying aircraft, space travel, etc. This paper describes the human experience with man-made sources of ionizing radiation, and reviews the population doses from medical and occupational exposures in Japan. Also the present review summarizes the studies of the dose estimations of primary radiations from atomic bombs and secondary radiations from neutron-induced radioactivities and of organ or tissue doses concerning on genetic effect and carcinogenetic effects of primary gamma-rays and neutrons.
Three types of ionization chamber survey meters and a type of GM counter survey meter were calibrated for measuring the β-ray absorbed dose rate in a working area. To estimate the β-ray absorbed dose rate, a survey meter was used without and with a filter. A reading of survey meter's indicator measured with the filter was subtracted from a reading measured without the filter, and then the absorbed dose rate was obtained by multiplying this remainder by a conversion coefficient. The conversion coefficients were roughly constant with distance more than 8cm (ionization chamber survey meters) and with distance more than 5cm (GM counter survey meter). The conversion coefficient was dependent on β-ray energies. In order to measure the absorbed dose rate of tissue whose epidermal thickness is 40mg/cm2, the constant value, 4(mrad/h)/(mR/h), was chosen independently of β-ray energies as the conversion coefficient of three types of ionization chamber survey meters. The conversion coefficient of the GM counter survey meter was more energy dependent than that of every type of ionization chamber survey meter.
Characteristic X-rays are emitted from ECR plasmas of various rare gases. In the case of krypton gas, its spectrum is regarded as to be monochromatic. It is found that the intensity depends on gas pressure under a constant microwave power and an optimum pressure exists for the maximum characteristic X-ray intensity. The discussion for the X-ray contrast and the patient exposure suggests the necessity of the monochromatic X-rays whose energy can be changed depending on the objects. The ECR plasmas which can produce characteristic X-rays of various elements may be promising as such X-ray generator.