In the roentgenography the patient is exposed with the skin dose of about 200mR, while in the fluoroscopy with the dose from 2 to 7R/min.
Among the radiation hazards induced by X-ray examination the incidence of genetic mutation and cancer is of importance.
When the nation wide Japanese gonad dose caused by X-ray examination is counted by referring with data of child expectancy, the genetically significant dose, GSD, which is estimated 26.5mrem/y in 1970 is obtained. It is well known that the leukaemia is induced by irradiation to the bone marrow. Leukaemia significant dose which is counted by the similar way to that of the genetically significant dose is thus estimated 169mrem/y in 1969.
Both of the genetically significant dose and the leukaemia significant dose caused by X-ray examination are much more high than those caused by the debris of the explosions of the atomic weapons and miscellaneous radiation source.
In order to reduce the patient dose, the education or training of correct establishment of clinical judgement should be encouraged. Beam limitation in the X-ray examination is the most effective means to reduce the patient dose, in particular, gonad dose and bone marrow dose.

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Minimum detectable body radioactivity, the relation between the detection efficiency and source to detector distance, state of sources, dependence of detection limit to γ-ray energy and influence of the variation of background level are studied with a simple scintillation counter widely used in radiation facilities. The results show that most of γ-emitting nuclides of 0.1μCi are able to detect by a simple scintillation counter in the room without special shielding.
Effect of collimating shield of the detector to detection limit and the relation between the optimum counting condition and the background level, partition of counting time for sample and background are discussed.

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Studies have been made to obtain the release limits of radioactive gas from a stack in normal operation of a BWR plant. These included observation of the behavior of radio-nuclides in the plant system and determination of significant nuclides, referring to the data gained by the operation of the JPDR (JAERI), and also the evaluation of exposures at ground surface around the plant site due to the released noble gas cloud.
It was found that the gamma exposure from a fission noble-gas cloud is a determining factor for the release limit from a BWR plant. The release limit of fission noble gases (diffusion mixture) from the JPDR with a 55-meter high stack is calculated as 47Ci/h for the dose limit of 0.04rem per 3 months under the meteorological stability D and a yearly average wind-speed of 3.6m/sec.

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