Dicentric formation in a fast neutron beam

Measurements were recently made at the Pretoria Cyclotron of the National Accelerator Centre of the CSIR, utilizing the new fast neutron facility. The purpose of the experiment was to identify a biological expression from which an average neutron energy could be inferred in order to compare it with that of the neutron beam generated at Hammersmith Hospital, London. The same nuclear reaction is used to produce fast neutrons at both institutions and the physical characteristics of the two cyclotrons are very similar. Deuterons were accelerated to an energy of 16 MeV to produce fast neutrons via the 9Be(d,n)10B reaction. Published literature has verified a continuous neutron spectrum with a maximum energy of about 16 MeV and a mean neutron energy of 7.6 MeV. Chromosome aberrations of human lymphocytes were used for comparison purposes and the dicentric yield was plotted as a function of absorbed dose. A quadratic function was fitted to the dose-response curve and the average neutron energy could be quantified in terms of the curve constants. The results obtained from this radiobiological measurement indicate that the physical characteristics of the Pretoria neutron beam compares favourably with that of the Hammersmith facility