Provisional Calculation of the Tolerance Flux of Fast Neutrons

Calculations suggest that the flux of fast neutrons corresponding in biological effects to a dose of 0·1 r of the usual filtered γ radiation from radium of approximate mean energy 0·8 Mev. delivered in 8 hours has the approximate constant value of 85 neutrons per cm.2 per sec. for neutrons of energy 2–20 Mev. On account of the uncertainties involved, it is recommended that the provisional tolerance flux of fast neutrons of energy 2–20 Mev. should not exceed 20 neutrons per cm.2 per sec. during a period of 8 hours in any one day. This value of the tolerance flux can be doubled for neutrons of energy 0·5 Mev.