NEUTRON TIME-OF-FLIGHT SIGNALS FROM EXPANDING OR CONTRACTING SPHERICAL SOURCES

The width of the energy distribution of fusion-produced neutrons is of ten used as an indication of the temperature of the reacting ions. The Doppler broadening of the neutron energy is due to the center-of-mass velocity of reacting ion pairs and is characterized by the ion temper ature for a Maxwellian distribution of ions with zero collective veloc ity. If there is bulk fluid motion or turbulence characterized by a ve locity on the order of the ion thermal speed, a significant additional broadening may be introduced. Suggestions of this phenomenon have bee n observed for two classes of laser targets. The first is a ''gas bag' ' target, in which a deuterated hydrocarbon gas is contained in a thin spherical membrane and illuminated uniformly. The second target is an ICF capsule with a deuterated plastic inner layer. In both cases, mea sured neutron energy distributions were wider than expected from theor etical ion temperatures and if interpreted as indicative of the ion te mperature, are inconsistent with the neutron yields observed.