Radiobiological studies with monoenergetic neutrons

The Radiological Research Accelerator Facility (RARAF) has the
capability of producing essentially monoenergetic neutron beams,
ranging in energy from 16.4 MeV down to 220 keV. In addition, two
lower energy neutron beams are available which consist of a wide
spectrum of energies and are described as the 110 keV and 60 keV
spectra. Seedlings of Vicia faba have been used to measure the
oxygen enhancement ratio (OER) and the relative biological
effectiveness (RBE) of each of these neutron beams. The OER
decreases as the neutron energy is reduced between 15.4 MeV and 220
keV, but does not appear to decrease further for lower energy
neutrons. RBE increases as the neutron energy is reduced from 15.4
AleV to 440 keV; the curve then goes through a maximum at around
350 keV, and for lower energies the RBE falls again.