An intercomparsion exercise on passive radon-and radon/thoron-devices was carried out under the participation of seventeen organizations in Japan during a one-year period from June 1992 to May 1993 in two Japanese traditional wooden houses, in which radon and thoron concentrations had been clearly measured beforehand. Methods used for the intercomparison were electrostatic collection using a solid-state nuclear-track detector (SSNTD), a thermoluminescent dosimeter (TLD) and a pin-photodiode detector (PPD) as detectors, cup methods with SSNTD using a filter cup, and a method using a bare SSNTD. Each participant selected a device or a method and a set exposure time; one, two, three, four, six, ten or twelve months. Radon and thoron concentration levels were about 20-50Bq/m3 for radon and 10-40Bq/m3 for thoron in the house in Nagoya, Aichi Prefecture, and about 5-30Bq/m3 for radon and 20-200Bq/m3 for thoron in the house in Seika, Kyoto Prefecture. The results of measurements for radon were as follows: in the case of the house in Nagoya, a great number of devices agreed at 20% deviation and all data entered in range twice; and in the case of the house in Seika, a larger deviation was found in the data. Measurements for thoron showed that there was clearly a discrepancy between concentrations obtained in each house, respectively, and that thoron concentration in the room decreased as distance from a wall increased.
A spherical plastic scintillation spectrometer has been developed for the determination of flux densities of cosmic-ray-charged particles around nuclear facilities. The accuracy of measured flux densities was improved by taking into consideration the pulse-height distribution caused by cosmic-ray photons and by the electro-magnetic interaction between cosmic rays and photomultiplier tube components. From the measurements performed in a natural environment, it became clear that the flux density of cosmic-ray-charged particles varied with the location, and in some cases almost 10 percent of the cosmic-ray-charged particles was shielded by the surroundings of the places monitored.
A past intercomparison on radon gas concentration measurements using radon integrating monitors revealed that a systematic difference (about 10 to 30%) existed between the estimated values of the National Institute of Radiological Sciences (NIRS) and those of the Environmental Measurements Laboratory (EML) of the USA and the Australia Radiation Laboratory (ARL). In order to find out the reasons, another intercomparison was conducted using an EML radon chamber in which both EML and representative Japanease research institutes participated. On this occasion, the main device were ionization chambers, the standard device in Japan. However, measurements of radon with radon gas integrating monitors and measurements of radon progeny were also taken simultaneously. Good agreement was obtained among estimated radon gas concentrations by the Japanese teams, though the values were lower than those of the EML by 5%. On the other hand, radon progeny concentrations were in agreement among all the participants within statistical uncertainty.
An extensive car-borne survey was made for the evaluation of dose rates due to environmental gamma rays in Hokkaido during the period from May 1994 to January 1996. The dose-rate levels in Hokkaido were estimated from survey results measured with a portable pure germanium spectrometer installed in a car. The car speed was kept between 30 and 60km h-1 (car-borne measurements). In addition to the car-borne measurements, another mode of measurement (spot measurements) was also made at 100 specific places selected in advance. The measurement times were set at 900s real time both for car-borne measurements and spot measurements. The survey routes covered almost all districts along the main roads in Hokkaido. From the car-borne measurements, absorbed dose rates in air due to gamma rays were found to be distributed from 14.9 to 116.5nGy h-1. The arithmetic mean dose rate and the standard deviation were calculated to be 42.1±16.2nGy h-1. The variation of total absorbed dose rate was found to be originated mainly by the variation of contribution from the Th-232 series nuclides.
In order to examine the dispersion of tritium released from the Takahama nuclear power plant into Uchiura Bay, seawater was sampled at three stations off the release point every two months. Tritium concentrations in these samples were determined. Simultaneously, the surface temperature of the seawater was also recorded at 25 points around the sampling stations. Observed data indicated that on those occasions when the sampling coincided with the release of tritium from the plant, the contribution of released tritium could be temporarily detected within the dispersion area of thermal effluent.