Neutron energy spectra of a 238Pu-18O(α,n) source - unmoderated and polyethylene moderated

Neutron energy spectra were obtained for a 238Pu-18O(α,n) source, both unmoderated and moderated. Moderation was accomplished by placing the source at the center of polyethylene spheres ranging in diameter from 7.6 to 30.5 cm. Measurements utilized a single NE213 scintillator fast-neutron spectrometer, precision long counter, and double moderator. Average energies ranged from 2.0 MeV for the unmoderated source to 1.1 MeV for the most heavily moderated. The fraction of neutrons in each spectrum with energies <1 MeV varied from 0.22 +- 0.09 to 0.64 +- 0.08, and the neutron fluence-to-dose equivalent conversions factors ranged from 3.3 X 10-5 to 2.7 X 10-5 mrem/n-cm-2, with the first figures in each case being for the unmoderated source. (author)