CALCULATIONS FOR THE HEAVY WATER MODERATED 252CF REFERENCE FIELDS AT PTB.

Abstract

Knowledge of the neutron spectra of reference fields is very important for calibration purposes. This paper presents new calculations of the neutron spectra and dosimetric parameters of a D2O moderated 252Cf source assembly used to produce a neutron reference field at the Physikalisch-Technische Bundeanstalt (PTB), based on recent 252Cf fission neutron spectrum data and conversion coefficients for operational radiation protection units recommended by the International Commission on Radiological Protection (ICRP) report 57. Neutron fluence and dose calculations were carried out using a detailed simulation model of the source assembly implemented using MCNP6 and the cross-section data library ENDF/B-VIII.0. The PTB moderator was compared with the International Organization for Standardization, ISO 8529 model and to previous calculations done at PTB. The results show differences to the previous calculations performed at PTB of the order of 5% and a slight discrepancy with the ISO 8529 moderator model regarding the values of the operational quantities.