Abstract

Color-sorted spherical molten particles extracted from Moto-Ujina Beach sand were analyzed by inductively coupled plasma–mass spectrometry, thermal ionization mass spectrometry, micro-PIXE analysis to obtain the elemental concentrations, ²³⁵U/²³⁸U isotope ratios, and elemental concentrations and mapping, respectively. Micro-PIXE analysis was also performed for molten particles produced by fireworks, which are likely to be an artificial background for molten particles at Moto-Ujina Beach. A computer simulation was used to investigate whether the Hiroshima atomic bomb impact soil dust (mineral particles) from the near-surface could reach melting temperatures under atomic bomb fire ball-cloud conditions. The modelled temperature changes were monitored and analyzed by placing tracer particles in the explosion model calculation. The temperature rose to a maximum of approximately 1250 K (about 980 °C), which was lower than the glass particle formation temperature (2073–1673 K). The results could not determine with certainty that the particles collected at Moto-Ujina Beach derived from the A-bomb. However, even if some of the Moto-Ujina particles were formed by the atomic bomb, it would be difficult to use them as indicator materials for fallout owing to the background firework particles.