CR-39を用いたレーザー駆動陽子線計測における光中性子起因エッチピット弁別手法の開発

摘要

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 using CO_2 clusters embedded in H2 gas conducted with the J-KAREN laser facility (1 J, 40 fs) at JAEA-KPSI, the energy of the electrons reached as high as 200 MeV. Such fast electrons can produce photo-neutrons by bremsstrahlung processes followed by (y, n) 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 laseraccelerated protons and photo-neutrons on CR-39 based on the incident angle and the incident energy.