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 neutrons emitted in intense bursts by an extension of time of flight spectroscopy. The experiment consists of recording the signals of a number of detectors placed at various optimized distances from the source. The evaluation is based on a new Monte-Carlo reconstruction method which 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 presented. Time resolution better than 10 ns and energy resolution of about 50 keV is possible. It is also shown that in the case of dense Z-pinch experiments characterized by shorter emission times (20–40 ns) the method still works for flight bases not longer than a few meters. The application 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 energy, is illustrated.