A Diagnosis of laser-accelerated ion beams considered with photo-neutrons contaminants

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 target, along with high energy ions, a significant amount of well-collimated high energy electrons with several hundreds of MeV are produced. Such fast electrons could produce high energy photons via bremsstrahlung processes. Furthermore, such photons could produce photo-neutrons in a series of (,n) reactions. If CR-39 detectors, which can detect only ions and it is insensitive to high energy photons and electrons, is exposed to such photo-neutrons, it can record recoiled protons and other heavy ions generated by the nuclear reactions. In order to precisely diagnose only for laser accelerated ions, we have to keep the photo-neutron flux level as low as possible, because it could cause significant contaminant effects to the CR-39 as a background noise. In the present study, to minimize the flux of photo-neutrons, we have considered the geometry of the stacked CR-39 detector unit by using Monte Carlo simulation.