Apparatus development for measurement of 134Cs and 137Cs radioactivity of soil contaminated by the Fukushima Daiichi Nuclear Power Plant accident

We developed an apparatus containing a NaI(Tl) scintillator to measure the 134Cs and 137Cs radioactivity of soil contaminated by the Fukushima Daiichi Nuclear Power Plant accident. The unfolding method with the least-squares technique was used to determine the radioactivity. Detector responses for each radionuclide in soil were calculated with EGS5 code for the unfolding method. The radionuclides that were measured were 40K, 134Cs, 137Cs, 208Tl, 214Bi, and 228Ac. The measured spectrum agreed well with the spectrum calculated from the response matrix and measured radioactivities. The unfolding method allows us to use the NaI(Tl) scintillator despite the overlap of peaks.