The effect of implosion geometry and multiple scattering on the down-scattered DD-neutron spectrum for areal density diagnosis

Down-scattered neutron spectra for different areal densities and different hot-spot sizes are simulated via using Monte Carlo method. The simulation results indicate that there is a nearly linear relationship between fuel areal density and the yield ratio of down-scattered neutrons to primary neutrons. The linear coefficient varies with areal density and hot-spot size. Single scattered and multiple scattered neutron spectra are simulated to discuss the influence of multiple scattering on down-scattered neutron spectrum. For indirect drive target at SG-III prototype and direct drive target at OMEGA, the effect of CH shell on down-scattered neutron spectrum is simulated.