Optimal foil shape for neutron time-of-flight measurements using elastic recoils

The basis for a time-of-flight neutron spectrometer for inertial confinemen t fusion (ICF) experiments using recoils from a shaped scattering foil is p resented. It is shown that the number of elastic recoils can be substantial ly increased by utilizing a large scattering foil in the shape of an ellips oid, with the curvature of the ellipsoid being determined by the mass of th e recoil particle. This shape allows the time-of-flight dispersion - presen t originally in the neutrons - to be maintained in the recoils despite the large foil area. The feasibility of using this design on current ICF experi ments is discussed. (C) 2001 American Institute of Physics.