Fig. 4-19 The distribution of absorbed dose rates in air due to gamma rays in the Chernobyl area by carborne measurements. The mean dose rate in a 5 x 5 km region is shown by a color bar. The red circle indicates the 30 km zone that the public is not allowed to enter.

Fig. 4-20 A carborne survey system developed at JAERI. The vehicle position, identified from communication with artificial satellites, and the dose rate are recorded and shown on the screen every 10 seconds.

The environment around the Chernobyl power plant is still contaminated because of the accident in 1986. Accurate information about the contamination would be a great help for estimating the radiological consequence and for taking appropriate countermeasures for recovery. Further, it is important to establish survey methods for contaminated environments in case such an accident occurs in Japan. From these perspectives, JAERI has conducted an investigation of the contamination in the Chernobyl area in cooperation with the Chernobyl Center for International Research (CHECIR). The detailed distribution of absorbed dose rates in air in the area has been determined by carborne measurements using a radiological survey system developed at JAERI. Direct measurements made in some regions outside the 30 km zone show the dose rate is quite high, even though people can enter this zone with ease. However, the dose rates in some regions inside the zone are nearly as low as those in Japan. Also, regions having a high dose rate were found to exist very close to regions having a low dose rate. Further, the carborne survey technique developed at JAERI has been validated by these measurements.

Reference T. Nagaoka, et al., Radiation Survey in Chernobyl; Proceediogs of the 36th Survey and Research Activities on Environmental Radiation in Japan (Science and Technology Japan), p.43- (1993).

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