Discrimination Method of Etch Pits Created by Laser-Accelerated Protons and Recoiled Protons by Photo-Neutrons Using CR-39

Abstract

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 CO₂ 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 (γ , 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.