DETECTOR DISTANCE SELECTION FOR NEUTRON TIME-OF-FLIGHT TEMPERATURE-MEASUREMENTS

Fuel ion temperatures for laser-driven, inertial confinement fusion targets are often determined by neutron time-of-flight (TOF) techniques. The error in the temperature measurement is a minimum at a target-to-detector distance that depends on both target and detector characteristics. The error is dominated by the detector response at shorter distances and by the number of detected neutrons at larger distances. We develop equations that relate the temperature error to the target ion temperature, the number of neutrons detected, target-to-detector distance, and the detector impulse response; and present sample calculations of error for D-D and D-T plasmas observed by typical Nova neutron TOF detectors. The detector placement is important for minimizing temperature error for target yield below 1010 neutrons.