Evaluation of the characteristics of the neutron reference field using D2O-moderated 252Cf source

The ambient/personal dose equivalent per fluence for D 2 O moderated 252 Cf neutron source was determined by measurement. An appropriate subtraction of the scattered neutrons is required for the accurate measurement of direct neutrons. A cubic shadow object was used for the subtraction of the scattered neutrons from the surroundings. The scattered neutrons to be subtracted vary with the position of the shadow object due to the large volume of the source. Using the Monte Carlo code MCNP-4C, the optimum positions of the shadow object were surveyed for subtracting the scattered neutrons. The energy spectra of direct neutrons were measured in the optimum position. The dosimetric parameters for the D 2 O moderated 252 Cf neutron source were reasonable, taking into account the uncertainties of the parameters.