Novel Method of Quantifying Radioactive Cesium-Rich Microparticles (CsMPs) in the Environment from the Fukushima Daiichi Nuclear Power Plant

Abstract

Highly radioactive cesium-rich microparticles (CsMPs) were released from the Fukushima Daiichi nuclear power plant (FDNPP) to the surrounding environment at an early stage of the nuclear disaster in March of 2011; however, the quantity of released CsMPs remains undetermined. Here, we report a novel method to quantify the number of CsMPs in surface soils at or around Fukushima and the fraction of radioactivity they contribute, which we call "quantification of CsMPs" (QCP) and is based on autoradiography. Here, photostimulated luminescence (PSL) is linearly correlated to the radioactivity of various microparticles, with a regression coefficient of 0.0523 becquerel/PSL/h (Bq/PSL/h). In soil collected from Nagadoro, Fukushima, Japan, CsMPs were detected in soil sieved with a 114 μm mesh. There was no overlap between the radioactivities of CsMPs and clay particles adsorbing Cs. Based on the distribution of radioactivity of CsMPs, the threshold radioactivity of CsMPs in the size fraction of <114 μm was determined to be 0.06 Bq. Based on this method, the number and radioactivity fraction of CsMPs in four surface soils collected from the vicinity of the FDNPP were determined to be 48-318 particles per gram and 8.53-31.8%, respectively. The QCP method is applicable to soils with a total radioactivity as high as ∼10 Bq/kg. This novel method is critically important and can be used to quantitatively understand the distribution and migration of the highly radioactive CsMPs in near-surface environments surrounding Fukushima.

Radioactivity and radionuclides in deciduous teeth formed before the Fukushima-Daiichi Nuclear Power Plant accident

“…We measured radioactivity in deciduous teeth collected between January 2014 and December 2016 using IP, which have become valuable radiation research tools [25][26][27] . One advantage is that IP have high sensitivity with an excellent linear response ranging over three orders of magnitude.…”

First isolation and analysis of caesium-bearing microparticles from marine samples in the Pacific coastal area near Fukushima Prefecture

“…P2 flowed southwest toward the Tokyo Metropolitan Area (TMA). Ikehara et al 33 showed by an autoradiography analysis of IP of contaminated soil samples that both P2 and P3 (emitted on the afternoon of 15 March 2011) contained Type-A particles. P3 flowed first toward the central part of Fukushima Prefecture, and later northward and northwestward.…”

Finding Radiocesium-bearing Microparticles More Minute than Previously Reported, Emitted by the Fukushima Nuclear Accident

“…Some recent research proposed that CsMPs can be distinguished from radiocesium-sorbing minerals by the intensity of radioactivity per individual particle. 13,14 The radioactivity of CsMPs is approximately proportional to their volume, 15 and as an example, the minimum CsMP reported to date had a diameter of 1.3¯m and 137 Cs radioactivity of 0.43 Bq. 14 In contrast, WB and other mineral grains of several dozen microns possess radioactivity on the order of 10 ¹2 Bq, at most.…”

“…16 Therefore, empirically there is a gap in radioactivity between CsMPs and mineral grains, such as WB. Using this gap, it was suggested that "hot spots" with more than 10 ¹2 Bq on an imaging plate (IP) are classified as CsMPs, 13,14 although distinction of CsMPs from radioactive mineral grains is not possible due to the low spatial resolution of IP. However, this gap may be an artifact for the following reasons.…”

“…Their radioactivity was estimated from the integrated photostimulated luminescence intensity calibrated by the radioactivity of CsMPs preliminarily determined using a germanium gamma-ray spectrometer (GCW2523S, Canberra). 13,17 The radioactivity was corrected to that on March 14, 2011. The radioactivity of the particle shown in Figure 1c was also measured using the germanium gamma-ray spectrometer.…”