Development on an Omni-directional Radiation Detector for High Dose Gamma-Ray

Abstract

We are required the distribution of radioactivity in the building to proceed with the decommissioning of TEPCO’s Fukushima Daiichi Nuclear Power Plants. Therefore, we developed and evaluated a compact and portable omni-directional radiation detector (FRIE) which can be used in high-dose environment. FRIE arranges the scintillators in the Sierpinski’s tetrahedron shape which is fractal shape. Combined with the FRIE’s counting rate and Maximum Likelihood Expectation Maximization method, the radioactivity distribution can be imaged in three-dimensions. In this study, we evaluated the accuracy of the radioactivity distribution estimation by simulation when random errors were introduced to the measurement positions. The radioactivity distribution was also imaged threedimensionally by a laboratory test using ¹³⁷Cs sources. As a result, it was found that the source position can be measured with almost no error if the measurement position error is within 0.2 m. It was also possible to determine the location of the sources and estimate the approximate radioactivity intensity of the sources after only a few minutes of measurement.