Time-dependent multiplicity for Cf-252 neutron source

A Cf-252 neutron source is widely used for testing and calibrating neutron multiplicity counters. General equations for calculating the time-dependent strength and multiplicity of Cf-252 sources are deduced based upon the decay model of Cf-252, Cf-250, and their daughter products Cm-248 and Cm-246. With the nuclear data of these four nuclides, an instance of a long-aged (>40 a) Cf-252 source is presented to illustrate the variation of the strength and multiplicity with time; the calculation results indicate that the 1st, 2nd, and 3rd moment factorials of the neutron multiplicity are significant decreased compared to the ones of nuclide Cf-252. For verification, a neutron multiplicity counting experiment for this Cf-252 source (I#) and another Cf-252 source (II#) with 17.1-year service life was carried out respectively using a thermal neutron multiplicity counter. The measured results are consistent with the calculation results from equations. The results from this study help to understand the changes in attributes with respect to time for any Cf-252 source while making appropriate corrections for obtaining accurate calibration results. •The time-dependent strength for Cf-252 neutron source was investigated and well-known.•However, the time-dependent neutron multiplicity for Cf-252 neutron source are lack of investigation.•This data is essential for neutron multiplicity counter calibration in the field of nuclear material assay and accountability.•In this paper the time-dependent neutron multiplicity for Cf-252 neutron source are deduced and verified with experiment.