Recent amendments to the Law concerning Prevention of Radiation Hazards due to Radioisotopes, etc. and related regulations might afford the use of unsealed radioisotopes below the exemption limits outside controlled areas. This drastic change brought a great convenience to radiation workers, however, the practical management should take safety of both non-radiation workers and environments into consideration. Analysis of research activities using unsealed radioisotopes and a survey for radiation workers in Nagasaki University revealed that a number of biochemical experiments could be performed using radioisotopes below the exemption limits and that a half of respondents desired to use them in their own laboratories. Radiation safety management of those areas was also favored by most of responders, which would increase tasks of radiation safety staffs. Therefore, the rational and affordable safety management practice is required. On the basis of these results together with radiation safety managements in the U. S., Canada and the U. K., practical considerations for the use of radioisotopes outside controlled areas in Japan are discussed.

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A new attempt has been carried out for providing an additional function of particle identification for the imaging plate of two-dimensional position sensitive device. This proposed method is based on the statistical feature that PSL intensity recorded in a small pixel may suffer from fluctuation even though the PSL intensity seems to be almost uniform in a larger area. Dividing a scan area of about 3 mm square into more than 1, 000 pixels of 0.1 mm square, frequency distribution in PSL intensity became sharper with increasing β-ray irradiation time. The broadness was quantified by the standard deviation obtained by fitting measured distribution to Gaussian. It was experimentally confirmed that the standard deviation for α-rays was much higher than that for β-rays on the condition of the same average PSL intensity, which means that α-and β-rays can be successfully discriminated by the proposed method. From a viewpoint of practical application to monitoring of radioisotope contamination in controlled area, two problems were also investigated concerning about the mixed irradiation of α-and β-rays and the minimum scanarea for deriving distribution.

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For accurate and efficient radiation safety management in facilities using radioisotopes, two-dimensional barcode (2-DC) was applied to the optical identification of radiation sources and personal dosimeters. The mobile personal computer (PC) equipped with a barcode reader, which has imported inventory records from the pre-existing radiation management system, enabled us to finish inventory procedures for 170 2-DC-labelled radiation sources in as short as 20min by one person. Identification of 270 personal dosimeters in their monthly replacement procedures also successfully completed within 20 min by incorporating pre-labeled 2-DC to PC installed with inventory records of dosimeters and radiation workers. As equipments and software required for 2-DC are affordable, easy to operate, and potentially expandable, the introduction of 2-DC system may help to establish practically higher level of radiation management.

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The control of working environment has been one of the most important duties for any companies to prevent occupational disease. In case of the controlled area using unsealed radioisotopes, measurement of the concentration of airborne radioactive material should be carried out. Then, we report the measurement performed at Tottori University and the results obtained from April 2004 to February 2006. As the results obtained from 3, 105 points, concentrations of radioactive material in all working places of 99% were below detection limit. Only 26 points were detected, but the maximum concentration levels were 0.036 of the limit.

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According to the Working Environment Measurement Standards, we have been measured the concentration of radioactive substances (radioisotopes) in the air at working rooms for handling radioisotopes for two years. The detection limit values of total γ-emitter and total β-emitter are 3.7×10^-6 and 3.4×10^-7 Bq/cm³, which are lower than 0.5% of their concentration limits in air. In almost all facilities, none of such radioactivities were detected. In only few rooms, the concentration of ³H and ¹⁴C were slightly higher than the detection limits. In the case of our university, all data obtained represented the fact that the concentration of radioisotopes in the air at all the working rooms using radioisotopes has been kept far below the limit of regulation.

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A portable monitoring system of airborne radioactive materials was developed for sequential monitoring of many workrooms. The system consisted of a room dust monitor detectable for the particulates emitting beta rays with its maximum energy higher than 0.15 MeV and a personal computer connected with a multichannel interface. The characteristics of background activity resulted from airborne radon progeny were investigated. The background activity in a well ventilated workroom was relatively low and equilibrated in 3-4 h after the start of sampling. Moreover, it was affected by the change of atmospheric pressure. The minimum detectable activity for ³²P with the system was estimated to be 2.3×10^-5 Bq cm^-3 for 10 min measurement, which was less than 1/10 of the limit of airborne radioactivity concentration. The system is suggested to be more suitable than the conventional methods for the monitoring of airborne radioactive materials in the working environment.

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