Positron annihilation methods by -rays produced in laser-induced compton-backscattering

Hirade, Tetsuya  ; Toyokawa, Hiroyuki*; Odaira, Toshiyuki*; Suzuki, Ryoichi*; Ogaki, Hideaki*

Positron annihilation methods are very unique and strong tools to investigate materials. However, positrons are usually injected from outside of the samples. Therefore the samples should be in a vacuum or radioisotopes should be attached. Recently, Selim et al. applied high-energy g-rays (2MeV) produced by use of 6MeV electron linac to create positrons in thick materials. We have also been trying a similar method. In our case, high-energy -rays (20MeV) produced in laser-induced Compton-backscattering are applied for positron creation in samples. The -rays do not spread and penetrate straightly in air. When you place a sample on the path of -rays, positrons are created in the sample and usual positron annihilation methods can be applied. Moreover, It is not needed to place the samples in vacuum and radioisotopes are not necessary. It means that the measurements of very high temperature materials such as metals near/over melting points will be possible. The detail of this method and some examples of experimental results will be introduced.