Design of a measurement system for laser-accelerated ion beams considering photo-neutrons effect

Kanasaki, Masato*; Jinno, Satoshi*   ; Sakaki, Hironao; Kondo, Kiminori; Oda, Keiji*; Yamauchi, Tomoya*; Fukuda, Yuji

In laser-driven ion acceleration experiments using cluster-gas targets, a significant amount of fast electrons are produced that drive ion acceleration along with high energy ions with several-tens of MeV. In our recent experiment, the energy of the electrons reached as high as 200 MeV. Such fast electrons can produce photo-neutrons by bremsstrahlung processes followed by (, ) reactions. When the CR-39 nuclear track detector is exposed to such photo-neutrons, it records the etchable tracks of recoiled protons depending on their energy as unwanted background signals. To precisely diagnose laser-accelerated protons using CR-39, we have developed the discrimination method for laser- accelerated protons and photo-neutrons on CR-39 based on the incident angle and the incident energy.