A MONTE-CARLO TECHNIQUE FOR THE RECONSTRUCTION OF TIME-DEPENDENT SPECTRA OF SHORT-PULSE NEUTRON SOURCES

A method is presented which yields time-resolved energy spectra of neu trons emitted in intense bursts by an extension of time of flight spec troscopy. The experiment consists of recording the signals of a number of detectors placed at various optimized distances from the source. T he evaluation is based on a new Monte-Carlo reconstruction method whic h is also a powerful tool in designing and optimizing the experiment. Extensive numerical tests which simulate the application of the method for determining the time-resolved energy spectrum of fusion neutrons emitted by a plasma focus generator (pulse duration 20-500 ns, energy domain centered at 2.5 MeV and energy widths of 100-1000 keV) are pres ented. Time resolution better than 10 ns and energy resolution of abou t 50 keV is possible. It is also shown that in the case of dense Z-pin ch experiments characterized by shorter emission times(20-40 ns) the m ethod still works for flight bases not longer than a few meters, The a pplication of the Monte-Carlo reconstruction method to an experimental data set collected at the high voltage plasma focus SPEED 2, operated at 180 kV bank voltage, 1.5 MA pinch current and 65 kJ capacitor ener gy, is illustrated.