Recoil Energy Effects in High Energy Particle Irradiation

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Point defect clusters produced from collision cascades are very small and the identification of their nature was not easy. The establishment of radiation hazard control area on High Voltage Electron Microscopy Laboratory of Nagoya University has enabled to irradiate neutron irradiated radioactive samples with high energy electrons, and the reliable identification became possible from the behavior of each defects under electron irradiation.Further progress was made on the research of fusion neutron (RTNS-II) irradiated samples, and the controlled irradiation with a fission reactor (JMTR) proceeded to temperature-cycle irradiation and irradiations with multi-section removable rigs to obtain the data on the continuous progress of defect structure evolution. Direct comparison of fission neutron irradiation with those of fusion neutron irradiation became possible for the first time.Accumulation modes (irradiation dose phi) of defects produced directly from collision cascades were clarified from summing up the result of fusion and fission neutron irradiatoin and light and heavy ion irradiation : Very early stage by impact effect from collisions (phi^2), Simple stage proportional to irradiaton dose (phi^1), Stage with recovery by the reaction of freely migrating interstitials (phi^<1/2>), and Stage of geometrical overlap of defects (1-exp (-alphaphi) ).Applying the result of easy motion of small interstitial clusters obtained from electron irradiaton experiment to neutron irradiation, unsolved problems such as crystallographic orientation dependence were solved. Also, applying the fluctuation of point defect reactions obtained from electron irradiatoin, the origin of very small success probability of interstitial cluster growth from small interstitial clusters made by collision cascades was understood.