Measurement of fast neutrons and secondary gamma rays in graphite

The spatial fluxes and energy distributions of fast neutrons, total gamma rays and secondll:ry gamma rays transmitted through different thicknesses of graphite have been measured. The graphite samples were arranged in front of one of the horizontal channels of the ET-RR-J reactor. Gamma ray measurements were carried out for bare, cadmium filtered and boron carbide filtered reactor beams. A fast neutron and gamma ray spectrometer with a stilbene crystal was used to measure the spectrum of fast neutrons and gamma rays. Pulse shape discrimination using the zero cross over technique was used to distinguish the proton pulses from the electron pulses. The total fast neutrons macroscopic cross section and the linear attenuation coefficient for gamma rays were derived both for the whole energy range and at different energies. The obtained values were used to calculate the relaxation lengths for fast neutrons and gamma rays