Apparatus and method for separating neutron-induced .sup.4He (or other nuclei) recoil from background, which is predominantly gamma-ray induced electrons and cosmic rays, using software analysis of digitized electrical pulses generated in a six tube, high-pressure (11 bar) helium-4 (.sup.4He) detector, are described. Individual electrical pulses from the detector were recorded using a 12-bit digitizer, and differences in pulse rise time and amplitudes, due to different energy loss of neutrons and gamma rays, are used for neutron/gamma ray separation.
STATEMENT REGARDING FEDERAL RIGHTS
 This invention was made with government support under Contract No. DE-AC52-06NA25396 awarded by the U.S. Department of Energy. The invention was also supported in part by the Defense Threat Reduction Agency (DTRA) of the Department of Defense. The government has certain rights in the invention.