The Effect of photo-neutrons on diagnostics using CR-39 for laser-accelerated ion beam

Kanasaki, Masato; Fukuda, Yuji; Sakaki, Hironao; Yogo, Akifumi; Jinno, Satoshi   ; Nishiuchi, Mamiko; Hattori, Atsuto*; Matsukawa, Kenya*; Kondo, Kiminori; Oda, Keiji*; Yamauchi, Tomoya*

In laser-driven ion acceleration experiments applying cluster-gas targets, a significant amount of high energy electrons are produced. Such fast electrons can produce photo-neutrons via bremsstrahlung processes followed by (,n) reactions. When the CR-39 is exposed to photo-neutrons, it records etchable tracks of generated ions depending on their species and energy as background noises. To minimize the effect of photo-neutrons, the configuration of the CR-39 detector unit and beam dump for high energy electrons has been examined by Monte Carlo simulations. As a result, we have found the suitable configuration for CR-39 to detect only laser-accelerated ions with less contaminant by photo-neutrons in one laser shot.