Fast-neutron facility for biological exposures in an Argonaut reactor: design, tissue dosimetry and neutron spectrometry.

Small and medium-sized animals can be exposed to fast neutrons from a 235U-converter. Studies using tissue-equivalent ionization chambers in combination with a neutron-insensitive γ-ray dosemeter show that the γ-ray and thermal neutron contaminations in the animal exposure field are small, amounting to 8% and 0.7% respectively of the total kerma. Forty mice may be irradiated simultaneously at the same fast-neutron centre-line dose rate up to a maximum of 10 rad min-1. The neutron spectrum, determined by proton-recoil spectrometry, gives a mean neutron energy of 1.04 Mev. For the first-collision recoil protons a track-average LET∞, equal to 57 kev per μm has been calculated.