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

レーザー誘起コンプトンバックスキャッタリング$$gamma$$線による陽電子消滅法

平出 哲也 ; 豊川 弘之*; 大平 俊行*; 鈴木 良一*; 大垣 英明*

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

陽電子消滅法はとてもユニークで重要な手法であるが、陽電子は通常試料外部から入射する。そのため、試料は真空中に置くか、放射性同位元素を試料で挟み込まなくてはならない。最近、SelimらはLinacを用いて2MeVの$$gamma$$線を作り、その$$gamma$$線で試料内部に陽電子を生成させることで、厚みのある試料内部を試料の破壊をせずに陽電子手法で観察することに成功した。われわれも同様の手法をレーザー誘起コンプトンバックスキャッタリング$$gamma$$線(20MeVまで)により試料内部に陽電子を生成させ試みてきた。この手法ではまっすぐに進む$$gamma$$線上に試料を置くだけでよく、試料は空気中,ガス中でも問題なく、例えば、高温試料,融点付近の金属などの陽電子消滅法による観察なども可能である。

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 $$gamma$$-rays ($$sim$$20MeV) produced in laser-induced Compton-backscattering are applied for positron creation in samples. The $$gamma$$-rays do not spread and penetrate straightly in air. When you place a sample on the path of $$gamma$$-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.

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