Reconstruction of D-D Neutron Energy Spectra with a Small Number of the Time-Resolved Neutron Detectors

Summary form only given. From a theoretical point of view, the reconstruction of time resolved energy neutron spectra with limited data is a highly underdetermined ill-posed problem. The energy spectra are reconstructed from time-resolved neutron signals which are recorded by several detectors in one direction at different distances. There are several theoretical approaches for the development of algorithms. In our case, one of these techniques (namely a Monte Carlo method) was used and consequently improved. The transformation was based on the scattering theory and it was applied specifically to the D-D fusion reaction. Our improvement included the usage of neutron detectors in various directions and thus it was possible to calculate the anisotropy in neutron energies. However, this improved technique could not be applied for the reconstruction of neutron energy spectra with a small number of neutron detectors (four and less detectors). Therefore we had to use a special procedure for this class of problems. The reconstructed time-resolved neutron energy spectra have two variables, energy and time. It means that we have a lot of possibilities of a reconstruction. In order to obtain the correct reconstruction, we need to know an approximate timeevolution of neutron emission. For that purpose, we used recorded waveforms of hard X-rays, voltage, and current derivative. Further we employed the knowledge about D-D reactions which produced neutrons with energies about 2.45 MeV (plusmn1.00 MeV). It was also valuable to compare neutron waveforms at two detectors which were placed in the opposite directions at the same distance from the source. All these pieces of information gave us closer specification of the time of neutron production. The time of neutron production was then estimated mainly from the nearest neutron signal and the energy of neutron was determined mainly from the most distant neutron detector. This procedure was applied to data processing from Z-pinch experiments.