Effect of focused ion beam processing on stainless steel studied by positron annihilation lifetime measurements

Minei, Shuntaro; Oshima, Nagayasu*; Sakai, Hiroaki; Okubo, Nariaki   ; Kondo, Keietsu  ; Suzuki, Ryoichi*; Hirade, Tetsuya  

In nuclear reactor materials, subnanometer-size vacancy type defects are induced by neutron irradiation. Although positron annihilation methods are effective techniques for evaluation of the vacancy type defects, it may be difficult to apply the methods for neutron irradiated samples, because of -rays from highly neutron irradiated, i.e. radioactivated, samples. Recently, positron micro beam has been developed at AIST. Therefore, we are suggesting that smaller radioactivated samples emit fewer -rays. Focused Ion beam (FIB) is one of the tools to prepare micrometer scale samples by ion sputtering, for example, for the transmission electron microscope. There is some possibility to have vacancy type defects in the samples induced by the FIB processing and it can make estimation of the pre-existing defects in the samples difficult. The results investigated by positron annihilation lifetime measurements for SUS316L showed that FIB can be applied.