In emergency survey, exposure dose rate responding detectors are used, in general, for the estimation of ground surface contamination in Ci/km2, but the process of estimating the deposited radioactivity from measurement of exposure dose rate has a great error because of the large photon energy dependence of dose rate-to-photon flux conversion. For this reason this estimation method is useful only for the simple release of one or two radioactive nuclides to the environments. On the other hand, photon flux at a given height above ground concerns directly with the disintegration rate of radioactive nuclides on ground surface. At this point of view, it is discussed in this paper to use a NaI (Tl) scintillation counter as a photon flux responding detector instead of the exposure dose rate responding one for environmental survey, and it is proved that the present method estimating the contamination level directly from its counting rate in cps is superior to the former method in its simple calculating procedure and in small conversion error.
This report describes the results of the test for sampling characteristics of some personal air samplers which are widely used for estimating the hazard due to inhalation of airborne harmful materials in the nuclear fuel plants and other industrial installations. The personal air samplers investigated are three kinds, namely, of the trade mark of MSA Monitaire Sampler, UNICO Mighty Mite and Casella MK II. In order to measure the flow rate of each sampler, a transducer was calibrated by means of other experimental procedure, before the flow rate tests were made. The battery capacity without the load and the maximum load under the constant voltage supply were also studied. The maximum flaw-rate without the load was about 5l/min in the UNICO, 4l/min in the MSA and 2l/min in the Casella, respectively. The sampling air volume of the UNICO sampler is, however, most decreased by the increase of load, compared with those of the Casella and the MSA samplers. Some other basic data useful for improving the characteristics of samplers were also obtained.
For the purpose of radiation protectien against X-ray diffraction apparatus, thc followings were carrried out: (i) Measurements of the exposure rates of the primary and scattered X-rays produced from the apparatus, (ii) Determinations of the sensitivity of many types of surveymeters for the low energy X-rays from the apparatus, and (iii) Experiments on the shielding effect of many kinds of materials such as vinyl sheet, rubber, etc.. Exposure rate of about 600R/min was observed for the primary X-rays at the sample holder of the apparatus under the normal operation. For the 8 keV X-rays emitted from the apparatus, the readings of an ionization chamber type surveymeter (ICS-10lC) which was dcsigned for X-rays were in good agreement with those of thc Victoreen r-meter, whereas the readings of the ionization chamber type surveymeter made for γ-rays indicated about one half of those of the Victoreen r-meter. The shielding effects of several materials such as polyethylen, rubber, cotton cloth, etc. were measured. Among them, vinyl sheet had the greatest shielding effect. Survery technique and assessment of absorbed dose are described in appendix.
This paper has evaluated the safety of ultimate disposal of solidified radioactive wastes into the ground. It was assumed that ten percent of radionuclides contained in the waste was eluted into the ground by accident. Migration rates of radionuclides in the ground, the dispersion of nuclides in the sea, concentration of nuclides in the seafood, and radiation dose to the human environment due to disposal of radioactive wastes into the ground have been estimated. The evaluation has shown that, under assumed conditions, this method of disposal was safe and promising.