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The sensitivity was obtained by solving a multi-group diffusion equation and by the experiment using monoenergetic neutrons. The neutron energies used were over the range of 0.625 eV to 10 MeV in the calculation and 5 KeV to 6 MeV in the experiments. Moderator thicknesses were 2.7, 4.7, 6.7, 7.9, 11.0 and 14.7 cm in the calculation, and 3.5, 4.5, 6.5, 8.5 and 14.0 cm in the experiments. The results show a good agreement between the experimental and theoretical sensitivities for the energies above 200 KeV, while slight discrepancies appear below this energy.

A new Rem-counter for neutrons was designed. The counter has two detector systems, one of which is a BF, counter embedded along the center axis in a 30-cm-diameter and 32-cm-height paraffin cylinder, and the other, three BF, counters embedded coaxially at intervals of 120 degrees around this axis.By using this counter, dose equivalent rates are measured within +30 per cent of errors for neutrons of typical spectra. The rough estimations of neutron spectra are also given by this Rem-counter.

A practical method applicable to field m'lnitoring 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 BF 3 proportional counter with paraffin moderators 6.5 em and 1.0 em thick, sheathed in 0.5 mm thick Cd, and a scintillation (ZnS and plastic) counter,The dose equivalent rate D(mremfhr) of neutrons with a broad spectrum is determined from the equation D=Da+Ds, where Da is the dose equivalent rate determined from the effective neutron flux and the effective neutron energy through the counting rates obtained with the BF 3 proportional caunter with paraffin moderators, and Ds 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.

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