Generation of radiocesium-bearing microparticles originating from the Fukushima nuclear accident by laser heating

In order to clarify the formation process of CsMPs, experiments to generate microparticles that simulate CsMPs were conducted. By heating three types of samples (a SiO₂-based mixture, a basalt, and a mixture of diatomaceous earth and artificial seawater) with a high-intensity infrared laser, spherical particles with diameters ranging from 0.1 to several micrometers similar to Type A-CsMPs were successfully generated. These particles are considered to be formed by vaporization and condensation of the sample heated by the laser, and a similar process can produce Type A-CsMPs. The source material for CsMPs is thought to be some kind of SiO₂-based material. If the basalt or diatomaceous earth/seawater mixture used as the sample for this study is the source material for CsMPs, it was found that additional materials including Zn and Sn must be mixed with them. It was also found that the presence of Al, Ca, and Ti differed between the bulk sample and the microparticles generated from it. This difference can be attributed to the low volatility of these elements. This difference in the presence of Al, Ca, and Ti between the bulk sample and the microparticles is similar to the difference in their presence in Type B- and Type A-CsMPs. This indicates that even if the main source material of the Type A- and Type B-CsMPs is the same, the difference in their formation process may explain some of the differences in elemental content. (author)