5:15 PM - 6:45 PM
[MAG33-P01] Analysis of Spherical Particles Extracted from Moto-Ujina Coastal Sea Sand
Keywords:black rain, melted particle, element analysis
Starting at the end of FY2020, soil sampling is underway at 100 sites with a 5 km mesh, including meteorological simulations and black rainfall areas, under a study commissioned by the Ministry of Health, Labor and Welfare. The soil analysis aims to identify undisturbed soil samples using the seismic distribution of 210Pb in the collected soil, and to determine the fallout from the atomic bomb by combining the depth distribution of 137Cs with information on fine charcoal and melted shpere particles. Melted shpere particles have been observed in the Fukushima Daiichi Nuclear Power Plant accident and are thought to have been produced at the time of the atomic bombing because they are produced at high temperatures associated with explosions.
On the other hand, a paper published by Wannier et al. (2019) reported the presence of approximately 3,000 tons of melted particles of high-temperature origin (approximately 1,800°C or higher) in the sand of the Moto-Ujina beach in Hiroshima City, and it was argued that the origin may reasonably be derived from the August 6, 1945 Hiroshima atomic bomb. It is possible that these molten particles are the same as the radioactive molten particles we were aiming for in our soil analysis, and if we can confirm that the Wannier molten particles originated from the atomic bomb, it is expected to make a significant contribution to soil sampling and analysis.
In FY2021, sea sand from the Moto-Ujina beach in Hiroshima Prefecture was collected for extraction of spherical molten particles, and 5.86 g of spherical molten particles were obtained . Using this sample, the concentrations of 137Cs, uranium, and thorium were determined by measurement with a Ge detector. The 137Cs concentration was 1.3 ± 0.5 mBq g-1, which is too low to be attributed to the molten particle atomic bomb. The uranium and thorium concentrations were 8.67 ppm and 20.06 ppm, respectively, which were similar to or slightly higher than those in the Ota Riverbed in Hiroshima City . These results indicated the possibility that the spherical molten particles may have originated from the city's soil. However, the 235U/238U ratio estimated by Ge measurement was 0.00673± 0.00503, a value consistent with the natural 235U/238U ratio within the error range. Considering these results, it was not sufficient to conclude that the spherical molten particles originated from the Hiroshima atomic bomb2).
In FY2022, we conducted trace element analysis by inductively coupled plasma mass spectrometry (ICP-MS) using 5.86 g of spherical molten particles to examine whether the spherical molten particles could be considered to have originated from the Hiroshima atomic bomb. As a result, more than isotopic 235U/238U ratios were detected in the yellow and silver molten particles, raising expectations that they may have originated from the atomic bomb. However, since this was a one-time measurement result and the error was large, it was thought that a confirmatory measurement was necessary. To confirm this, we performed a confirmation measurement by Thermal Ionization Mass Spectrometry (TIMS) at the Kyoto University Complex Research Institute and a confirmation measurement by Micro-PIXE analysis at the Quantitative Research Institute of Japan (QST). In this presentation, he results of our work, from extraction of molten particles to the results of TIMS and Micro-PIXE analysis are peresented.
On the other hand, a paper published by Wannier et al. (2019) reported the presence of approximately 3,000 tons of melted particles of high-temperature origin (approximately 1,800°C or higher) in the sand of the Moto-Ujina beach in Hiroshima City, and it was argued that the origin may reasonably be derived from the August 6, 1945 Hiroshima atomic bomb. It is possible that these molten particles are the same as the radioactive molten particles we were aiming for in our soil analysis, and if we can confirm that the Wannier molten particles originated from the atomic bomb, it is expected to make a significant contribution to soil sampling and analysis.
In FY2021, sea sand from the Moto-Ujina beach in Hiroshima Prefecture was collected for extraction of spherical molten particles, and 5.86 g of spherical molten particles were obtained . Using this sample, the concentrations of 137Cs, uranium, and thorium were determined by measurement with a Ge detector. The 137Cs concentration was 1.3 ± 0.5 mBq g-1, which is too low to be attributed to the molten particle atomic bomb. The uranium and thorium concentrations were 8.67 ppm and 20.06 ppm, respectively, which were similar to or slightly higher than those in the Ota Riverbed in Hiroshima City . These results indicated the possibility that the spherical molten particles may have originated from the city's soil. However, the 235U/238U ratio estimated by Ge measurement was 0.00673± 0.00503, a value consistent with the natural 235U/238U ratio within the error range. Considering these results, it was not sufficient to conclude that the spherical molten particles originated from the Hiroshima atomic bomb2).
In FY2022, we conducted trace element analysis by inductively coupled plasma mass spectrometry (ICP-MS) using 5.86 g of spherical molten particles to examine whether the spherical molten particles could be considered to have originated from the Hiroshima atomic bomb. As a result, more than isotopic 235U/238U ratios were detected in the yellow and silver molten particles, raising expectations that they may have originated from the atomic bomb. However, since this was a one-time measurement result and the error was large, it was thought that a confirmatory measurement was necessary. To confirm this, we performed a confirmation measurement by Thermal Ionization Mass Spectrometry (TIMS) at the Kyoto University Complex Research Institute and a confirmation measurement by Micro-PIXE analysis at the Quantitative Research Institute of Japan (QST). In this presentation, he results of our work, from extraction of molten particles to the results of TIMS and Micro-PIXE analysis are peresented.