Our research group conducts a variety of studies on off-site emergency preparedness and response. Here is an example of research results.
In a nuclear emergency, it is expected that the contamination screening will be conducted on a large number of vehicles and residents. The NRA’s manual shows that workers should use a Geiger-Mueller (GM) survey meter and so on. However, in order to conduct the screening more efficiently, it is expected that vehicle monitors will be utilized.
In this study, we conducted a performance test of vehicle monitors owned by some local governments to simulate the screening.
Sealed radiation sources were substituted for the contamination of Operational Intervention Level 4 (OIL4), the evaluation criteria to conduct simple decontamination in the contamination screening. The radiation source was attached practically to a tire and around wipers of a vehicle, and the counting rate of γ-rays from the radiation sources was measured using the “Gamma Pole”, the portable radiation portal monitor for vehicles manufactured by the Chiyoda Technol Corporation.
It is important that the development of a simultaneous measurement method for the contamination of a tire and around wipers in order to make the screening tests more efficient*1. To develop the measurement method, we considered the placement method of the Gamma Pole by using a monte-carlo-simulation code*2 and conducted vehicle driving tests using a new placement method in which the detectors are placed horizontally and vertically, respectively*3
As a result, the discriminative ability to detect contamination, which is necessary for achieving simultaneous measurement, was confirmed. The accuracy for tires was 100%, while that for wipers was 80%. We will continue to research measurement and operation methods using the Gamma Pole, such as a method for simultaneous measurement and evaluation of both the two contamination, and then develop an effective utilization of radiation portal monitors in contamination screening of vehicles in nuclear emergency.
