Influence of gamma rays on measurement of neutrons spectrawith spherical proportional counter of recoil protons

The energy responses of gamma rays from 50 keV to 10 MeV of a spherical counter filled with 1 MPa hydrogen and with a 30 mm diameter have been obtained by experimental measurement and Monte Carlo simulation. It shows that the energy deposited in the counter is focused near 100 keV and below. An experiment with Am-Be source and 137Cs source indicates that intense gamma rays of the 137Cs source have made great influence on the measurement of the neutrons spectra below 100 keV from Am-Be source. It can be concluded that the measurement of neutron spectra below 100 keV from fissionable materials would be affected by the intense gamma rays. According to the collective features of recoil protons and electrons ionization in the counter, it is feasible to discriminate the gamma rays from the neutrons by rise-time method.