<title>Development of lower-energy neutron spectroscopy for areal density measurement in implosion experiment at NIF and OMEGA</title>

Abstract

Areal density (pR) is a fundamental parameter that characterizes the performance of an ICF implosion. For high areal densities (pR> 0. 1 glcm2), which will be realized in implosion experiments at NIF and LMJ, the target areal density exceeds the stopping range of charged particles and measurements with charged particle spectroscopy will be difficult. In this region, an areal density measurement method using down shifted neutron counting is a promising alternative. The probability of neutron scattering in the imploded plasma is proportional to the areal density of the plasma. The spectrum of neutrons scattered by the specific target nucleus has a characteristic low energy cut off. This enables separate, simultaneous measurements of fuel and pusher pRs. To apply this concept in implosion experiments, the detector should have extremely large dynamic range. Sufficient signal output for low energy neutrons is also required. A lithium-glass scintillation-fiber plate (LG-SCIFI) is a promising candidate for this application. In this paper we propose a novel technique based on downshifted neutron measurements with a lithium-glass scintillation-fiber plate. The details of instrumentation and background estimation with Monte Carlo calculation are reported.