Relative sensitivity of tooth enamel to fission neutrons: Effect of secondary protons

In the case of in vivo neutron irradiation, tooth enamel is also exposed to secondary ionizing radiation produced in the biological tissues surrounding teeth. It was shown that elastic scattering of reactor neutrons by hydrogen nuclei in soft tissue produces secondary protons with sufficient energies for ionization in the enamel surface. The effect of secondary protons depends on the grain size of enamel powder; for hydrogenous build-up material, dose response of enamel relative to tissue dose increases from 0.012±0.006 (of corresponding value for Co60 photons) for grain size >0.8mm up to 0.029±0.007 for grain size <0.3mm. Dose response of enamel samples protected from secondary protons by aluminum foil was found to be independent of the grain size (0.007±0.006). It was estimated that for whole tooth configuration at neutron irradiation, dose response of enamel should be increased by a factor of about 1.1 due to dose enhancement effect of secondary protons formed in soft tissues.