Time-Dependent Multiplicity for Cf-252 Neutron Source

A Cf-252 neutron source is widely used for testing and calibrating neutron multiplicity 11 counters. General equations for calculating the time-dependent strength and multiplicity of 12 Cf-252 sources are deduced based upon the decay model of Cf-252, Cf-250, and their 13 daughter products Cm-248 and Cm-246. With the nuclear data of these four nuclides, an 14 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 15 16 moment factorials of the neutron multiplicity are significant decreased compared to the ones 17 of nuclide Cf-252. For verification, a neutron multiplicity counting experiment for a Cf-252 18 source (I#) and another Cf-252 source (II#) with 17.1-year service life was carried out 19 respectively using a thermal neutron multiplicity counter. The measured results are consistent 20 with the calculation results from equations. The results from this study help to understand the 21 changes in attributes with respect to time for any Cf-252 source while making appropriate 22 corrections for obtaining accurate calibration results.