A practical method for evaluating the neutron dose equivalent rate

A practical method applicable to field monitoring with survey instruments is presented, which permits evaluation of the dose equivalent rate for neutrons, the spectrum of which is unknown but with energy ranging from epithermal to fast. The detectors employed consist of a BF₃ proportional counter with paraffin moderators 6.5 cm and 1.0 cm thick, sheathed in 0.5 mm thick Cd, and a scintillation (ZnS and plastic) counter. The dose equivalent rate D)(mrem/hr) of neutrons with a broad spectrum is determined from the equation D=D_B+D_S, where D_B is dose equivalent rate determined from the effective neutron flux and the effective neutron energy through the counting rates obtained with the BF₃ proportional counter with paraffin moderators, and D_s the dose measured with the scintillation counter, the sensitivity of which is nearly proportional to the dose equivalent rate for neutrons above 2 MeV. The error in evaluating the dose equivalent rate by the present method has been calculated to be at most 60% for typical neutron spectra, in the energy range from epithermal to 10 MeV. (author)