Positron production by laser-Compton -rays and application to material study

Toyokawa, Hiroyuki*; Hirade, Tetsuya  ; Tomota, Yo*; Ishibashi, Toshihiro*; Sugaya, Satoshi*; Suzuki, Ryoichi*

The brittleness of materials might be affected by defects, dislocations and impurities. However it is not well understood. Clarifying these problems is very important to make reliable models for estimating the degradation of materials for atomic energy. Injecting high energy photons with more than 1.02 MeV to materials can produce electron/positron pairs. Collimated MeV-energy--rays with several mm diameters can produce needle shaped positron distribution. By use of the produced positrons, it is possible to make 3D views of defect distribution or cross section of electro/positron pair production at deeper region of materials. This method is expected to be applied for measurements in atmosphere or high-temperature/high-pressure environments. We succeeded to obtain CT images of the transmission view and electron/positron pair production cross section of reinforcing bars in concrete by use of 5 mm diameter 9.1 MeV -rays. We also measured S-parameters for defects in metal samples.