Supplementary experiments and theoretical consideration have been performed about a new method for particle identification with an imaging plate, which was proposed in the previous paper. The imaging plate was exposed to 137Cs γ-rays, 2 MeV-protons accelerated by a tandem Van de Graaff, X-rays emitted from a tube operated under the condition of 20-70 kV, as well as α-and β-rays. The frequency distribution in PSL intensity in a pixel of 100 μm x 100 μm was measured and the standard deviation was obtained by fitting to a Gaussian. It was confirmed that the relative standard deviation decreased with the average PSL intensity for every radiation species and that the curves were roughly divided into four groups of α-rays, protons, β-rays and photons. In the second step, these data were analyzed by plotting the square of the relative standard deviation against the average PSL intensity in full-log scale, where the relation should be expressed by a straight line with an slope of -1 provided that the deviation could be dominated only by statistical fluctuation. The data for α-and β-rays deviated from a straight line and approached to each saturated value as the average. PSL intensity increased. This saturation was considered to be caused by inhomogeneity in the source intensity. It was also pointed out that the value of interception on full-log plot would have important information about PSL reading efficiency, one of characteristic parameters of imaging plate.
Surface contamination tests by a survey meter and a wipe test method were made in order to stop handling nuclear materials at the old research facility, Faculty of Engineering, The University of Tokyo. The practical treatment for decommissioning of the nuclear research facility was introduced with the results of the surface contamination tests. There were some contaminated points found after floor sheets and ducts were removed. Both a survey meter and a wipe test method were effective as complementary methods.