DOSIMETRY OF HIGH-ENERGY NEUTRONS AND PROTONS BY BI-209 FISSION

Fission of Bi by neutrons and protons of energies above 50 MeV provide s a detector for the high energy part of cosmic ray neutron and proton doses received by personnel in commercial aircraft. A stack of damage track detectors and Bi radiators, of large total area, has been teste d and has adequate sensitivity. Knowledge of the fission cross section s for neutrons and protons is critical for such measurements. Contrary to a common assumption that these are nearly equal, both old and rece nt measurements and recent calculations show that sigma(Bi)(n,f) is mo re than twice sigma(Bi)(n,f). Calculations indicate that Bi fission ca n probably determine dose equivalents from high energy cosmic ray neut rons to within +/-30%, and from cosmic ray protons to within +/- 25%. The response is nearly the same for equal dose equivalents of cosmic r ay neutrons and protons. The accuracy for neutrons could be improved i f cosmic ray neutron spectra were better determined.