Background neutron flux determination at a depth of 3200 mwe underground

Measurements of the background neutron flux at a depth of 1230 m (3200 mwe) in a silver, lead and zinc mine at Broken Hill, New South Wales, Australia are reported. using 3He neutron counters, the thermal neutron flux and epithermal neutron flux have been determined. The effect of background gamma radiation on the resultant pulse height spectra is discussed and a procedure is given for the correction of the obtained spectra for the effects of this gamma background. In addition, the internal counts originating from radioactive trace elements in the construction material of the detectors are discussed and appropriate corrections are determined. Using Monte Carlo calculations the response of 3He detectors for neutrons of different energies is examined. The upper energy limit for detection of neutrons using 3He detectors directly (in absence of any moderator) is calculated.