Neutron and gamma spectroscopy for clinical dosimetry

Neutron and photon energy spectra were measured in different depths and lateral positions in tissue-equivalent phantoms exposed to a therapeutical 14.1 MeV neutron beam. Intensity weighted mass energy absorption coefficients were derived for application in ionization chamber dosimetry in mixed neutron-gamma fields. The resulting relative depth doses show that on the beam axis for depths in excess of 20 cm, gamma radiation contributes with more than 10% to the total dose; off the axis outside the direct beam neutron and gamma doses are comparable. The differences between these doses and those neglecting the spectra distribution increase with depth and with the distance from the beam axis.