Direct Evaluation Of High Neutron Density Environment Using (N, 2n) Reaction Induced By Laser-Driven Neutron Source

We demonstrate that (n, 2n) reactions are induced by a high-flux pulse of fast neutrons (similar to 1010 neutrons in similar to 1 ns) provided from a laser-driven neutron source (LDNS). The maximum energy of the broadband neutrons reaches a few tens MeV. Several kinds of metal targets are exposed to the fast neutrons. As a result, unstable isotopes, such as Mn, Co, Hf, and Au are produced by (n, 2n) reactions and (180)Hf( )m Hf-181, Mn-56, Au-198, and Co-60 are produced by (n, y) reactions. We evaluate the neutron fluence and energy spectrum using the activation method in conjunction with a time-of-flight measurement. The neutron fluence is determined to be (4.3 f 0.5) x 10(8) neutrons/cm(2) in the energy range from approximately 8 to 20 MeV at 8-mm downstream of the neutron source. The present scheme provides a method to evaluate high-density neutrons seen in stellar environments, which are expected to be generated from future LDNSs.