Portable time-of-flight fast neutron spectroscopy

A time of flight neutron spectroscopy system 100 comprising a first detector 120 positioned at a first distance 130 from a fission source 110, configured to detect a gamma-ray emitted from the fission source 110 and a second detector 140 positioned at a second distance 150 from the fission source 110, configured to detect a neutron emitted from the fission source 110. A computer system 160 which may include a mixed field analyser (MFA) to discriminate gamma and neutron interactions records the time of a gamma ray detection at the first detector to start a time window. Detection of a neutron at the second detector 140 within the time window, record the gamma and neutron detections as a coincidence event. The time difference between the detections determines time-of-flight and neutron energy. The first detector may be solid-state scintillator and the second a liquid scintillator. The system may be portable or for on-the-fly spectroscopy.