Dosimetric properties of p(90)+(Be + Ta) and p(101)+(Be + Al) neutrons

Dosimetric data were obtained for p(90) + (Be + Ta) and p(101) + (Be + A1) radiation with field size 9 x 11 cm at a 125-cm SSD impinging on a tissue-equivalent liquid phantom with density 1.10. The radiation was unfiltered or filtered by 10 cm of polyethylene. Dose rates measured with a 0.5-cm3 ion chamber at a depth of 5 cm ranged from 0.046 Gy min-1 microA-1 for filtered p(90) + (Be + Ta) to 0.11 Gy min-1 microA-1 for unfiltered p(101) + (Be + A1). Neutron time of flight energy spectra in air averaged above 10 MeV indicate mean neutron energies ranging from 42.0-51.4 MeV for the four beams under study. The central axis depths at which 50% dose attentuation occurred ranged from 15 to 20 cm for these beams. At 3 cm depth the gamma dose component of the total p(101) + (Be + A1) dose was 14.5%, or 17% with filtration.