Design of laser-accelerated ion beam measurement system considering photo-neutrons effects

Abstract

  In laser-driven ion acceleration experiments using CO₂(cluster) + H₂(gas) targets, a significant amount of energetic electrons are produced. In our recent experiment which has been conducted with the J-KAREN laser (1 J, 40 fs), the maximum energy of electrons reaches up to 200 MeV. Such high energy electrons can produce photo-neutrons via bremsstrahlung processes and (γ, n) reactions. If the CR-39 ion detector is exposed to photo-neutrons, it can record etchable tracks indirectly as background noises. In the present study, to minimize the effects of photo-neutrons, we have designed the laser-accelerated ion beam measurement system by using Monte Carlo simulation code. As a result of simulations, we have found the suitable configuration for CR-39 to detect only laser-accelerated protons with less background etch pits which derived from photo-neutrons in one laser shot.