Electron Microscopic Examination of Highly Radioactive Fail-Out Particles

Abstract

MICROSCOPIC examination of highly radioactive fall-out particles, produced by the series of large-scale nuclear test explosions carried out during September and October 1961, revealed that although they were quite or nearly spherical, their surface states were different from particle to particle and some of them were much creased or had small spherical particles attached to their surface¹. Electron microscopic examination followed by electron photomicrography has been carried out to examine their surface state in detail. A vacuum-evaporated silica film backed with evaporated carbon film was used for holding a sample particle. A small drop of benzene was put on the silica film which was supported on a 150 sheet mesh, then a sample particle which had been picked up by the tip of a fine needle was transferred into the drop seen under a microscope. The sample particle was left on the film after the drop evaporated out. Electron photomicrographs of four particles, A, B, C and Z, were taken. In Table 1 are given their diameters, radioactivities and fractionation factors for ¹⁴¹Ce + ¹⁴⁴Ce (ref. 2). Fig. 1 (1,2,3) gives electron photomicrographs of particles A, B and C, respectively. Small particles adhered to the surface are thought to be fine fall-out particles which are micron size or smaller³. Fig. 1 (5) is a close-up of a part of particle C. The diameter of this small particle is about l.4µ.