Secondary Radiations Induced by Laser-Produced High Energy Electrons and Photons

초록

High energy electrons and photons up to 50 MeV have been generated from the laser-driven plasma in APRI. Especially, these high energy photons collided on a chamber wall made by stainless steel can cause the secondary neutrons and protons. Because the threshold energy of the reaction is around 10 MeV, the outgoing nucleons have a kinetic energy up to 40 MeV. From the previous experimental results [1, 2], the cross sections concerning the secondary radiations were collected and plotted in figure 1. The main composition of a typical stainless steel 304 are Fe, Cr (17.5~20%), and Ni (8~11%). And the main natural abundances of Fe and Ni are 56Fe (91.8%), 58Ni (68.3%), and 60Ni (26.1%). At the gamma-ray energy region of 10~30 MeV, the secondary neutrons can be significant for the radiation shielding because of the giant resonance property of the Fe and Ni nuclei. When the 1010 numbers of 18 MeV energy photons are incident on a 1 cm2 area of 5 mm thick stainless steel, the estimated number of secondary neutrons is approximately 4.2×107.