Small and medium-sized animals can be exposed to fast neutrons from a 2S5U-converter. Studies using tissue-equivalent ionization chambers in combination with a neutron-insensitive 7-ray dosemeter show that the y-ray and thermal neutron contaminations in the animal exposure field are small, amounting to S?; and 0.77; 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". The neutron spectrum, determined by proton-recoil spectrometry, gives a mean neutron energy of 1.04 Mer. For the first-collision recoil protons a track-average LET, equal to 57 kev per pm has been calculated.

In a case of accidental overexposure of a person, it is important to obtain a