An experience of instrumental estimation of cumulative external doses using single grain luminescence retrospective dosimetry method with quartz containing samples from Fukushima prefecture, Japan

The accumulated external radiation doses were measured in samples taken in the areas of radiation fallout as a result of the Fukushima-1 NPP accident using optic-stimulated luminescent dosimetry. Quartz-containing samples (building bricks) were selected in several areas adjacent to the NPP (Minami-soma and Iitate settlements) in March 2014. To exclude the influence of biotite microparticles in the samples that do not have dosimetric properties, luminescent retrospective dosimetry was carried out by single quartz microcrystals. It was found that at a depth of 5-20 mm from the outer surface, the accumulated doses (after subtraction of background doses) for the sample from Minami-soma were 25±6 mGy and 73±18 mGy for the sample from the village of Iitate. At the same time, at a depth of 3-5 mm, the accumulated doses were significantly higher in magnitude and equal to 50 mGy and 140 mGy, respectively. The outer layers of samples with a thickness of up to 2.9 mm were excluded from the analysis in order to avoid uncontrolled reduction of the dosimetric signal due to external light exposure to quartz crystals. It was suggested that the analysis of profiles in thin layers of bricks may be useful to study the contribution of the dose from beta particles to the total dose from gamma-beta radiation. Meanwhile, the accumulated doses from gamma irradiation at a depth of 3-5 mm should be significantly less in comparison with measured ones, since at this depth there is no effect of electron equilibrium for gamma quanta of high energy. It was concluded that the increased accumulated doses at depths of 3-5 mm may be due to external irradiation by beta-particles of contaminated soil and/or an additional contribution of quantum radiation with low energy. This conclusion is important for the interpretation of possible biological effects in irradiation of, for example, human skin and eyes, as well as all surrounding biota by short-range radiation in large-scale radiological accidents at nuclear power plants. The first results of the study are presented, and further work continues.