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The contribution to the neutron energy spectrum due to absorption of a photon of given energy by any one of these processes will be proportional to the product of the partial cross section for that process and the number of photons at that particular energy. The energy of the released neutron is obtained from the kinematics of the process and the energy of the final state. The total spectrum is obtained by summing over the possible decay modes and integrating over the photon energy. For a compound the sum is also over the constituent elements with a weighting proportional to the relative abundances.
RESULTS
Neutron energy spectra in carbon, nitrogen and oxygen were calculated for various bremsstrahlung end-point energies and, from these, tissue spectra were calculated using the tissue equivalent molecular formula C5H._01ftN. As an example of the results, the photoneutron spectrum from tissue for a photon end-point energy of 28 MeV is shown in figure 1, together with the contributions from the constituent elements. The neutron spectra from tissue over the energy range from 12-30 MeV are summarised in table 1, where average neutron energies and kerma conversion factors are displayed.
Full details of this work can be found in the published report (Allen and Chaudhri 1982).
REFERENCES
1. Allen P D, and Chaudhri M A, (1982) Phys. Med. Biol. 27:553.
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3. Caldwell J T, Bramblett R L, Berman B L, Harvey R R, and Fultz S C, (1965) Phys. Rev. Lett. 15:976.
4. Caswell R S, Coyne J J, and Randolph M L, (1980) Rad. Res. 83:217.
5. Fultz S C, Caldwell J T, Berman B L, Bramblett R L, and Harvey R R, (1966) Phys. Rev. 143:790.
6. Schiff L I, (1951) Phys. Rev. 83:252.
