Analysis of fissile materials in hot particles using fission track technique and evaluation of environmental doses from luminescence measurements

In the 19th Chinese nuclear detonation test in the atmosphere, some hot particles were isolated from fallout debris, which was collected in Niigata University two days after the detonation. These spherical hot particles, consisting of several μm in diameter, were followed to the analysis of fission track technique using two mica detector assembly sandwiched the hot particles and neutron irradiation. Unexpectedly, the particles showed typical star-like dense track distributions owing to remaining fissile material within the particles. The content and kinds of fissile material was assumed by adjusting a geometrical situation to countable track patterns. As a result, the use of enriched uranium was supposed on the basis of applied thermal neutron combined with chemical separation between uranium and plutonium. When the resemble fission track method was also applied to melted or fused surface of some roof tiles collected at about 500 m from hypocenter of Nagasaki atomic bomb, the star-like tracks on the muscovite detector were revealed after the neutron irradiation of sample assembly in a reactor. These results offer certain evidence that micro-particles containing fissile nuclides of atomic-bomb origin remain on the roof tile surface. Pu-contents in some remnant particles were evaluated to be 0.72 - 5.72 x 107 atoms from the star-like track analysis. Additionally, shortening of track lengths was suggestive to the existence of particles in slightly deeper sites from the tile surface. Subsequently, accumulated γ-dose on some roof tiles, which were exposed at about 700 m from hypocenter of atomic bomb in Hiroshima, was evaluated from blue TL measurement of quartz extractants by regeneration method. The almost retrospective dose values of 13.9 Gy was verified to be derived from atomic bomb explosion. (author)