Dosimetric properties of neutron beams produced by 16-60 MeV deuterons on beryllium.

Beams of fast neutrons were produced by a variable-energy cyclotron, using the ${}_{4}{}^{9}{\rm Be}$ (d, n) ${}_{5}{}^{10}{\rm B}$ reaction. The Be target thickness was 12.1 mm; Benelex material was used for collimating the neutron beams. A field of 5 × 5 cm at 125-cm target-surface distance was used for most measurements; the phantom employed was a Lucite-walled tank filled with tissue-equivalent (T-E) liquid. The absorbed dose rate in terms of rad/min/μA was measured at deuteron (d) energies between 16-60 MeV and found to follow an ${\rm E}^{2.67}$ relationship; the results are in agreement with previous data at the lower energies. Central axis depth-dose data were measured using d energies of 16, 30 and 50 MeV; the depth of the 1/2 maximum dose was found to increase with energy from 8.5 cm at 16 MeV to 12.0 cm at 50 MeV. Positions of maximum dose buildup were measured with an extrapolation chamber; at the higher energies these maxima were ...