Characterisation of spherical recoil proton proportional counters used for neutron spectrometry

The Institute for Protection and Nuclear Safety (IPSN) standard neutron detector in the energy range 60–800 keV is a spherical proportional counter of HARWELL type SP2 nominally filled with 300 kPa hydrogen. It was characterised in the monoenergetic neutron fields of PTB at the energies of 144, 250 and 565 keV, where the neutron energy and fluence were determined with the PTB reference instruments. The neutron fields produced at the same energies with the accelerator facility of Bruyères-le-Châtel were then investigated with the calibrated SP2 counter and various PTB instruments in order to determine the mean energy and the neutron fluence. The energy scale and a neutron fluence monitor were calibrated.