240Pu Effective Mass of 238Pu and 242Pu in Relation to Passive Neutron Coincidence and Multiplicity Counting

The nondestructive assay of plutonium mass by passive neutron multiplicity counting requires accurate evaluated nuclear data to be available. In particular, the coefficients of the an important role in the validity of the calibration procedure. A new evaluation of these quantities, both for double and triple coincidence counting, is presented following measurements of in a neutron multiplicity chamber. Empirical double and triple coincidence count rates have been corrected for neutron multiplication, detection efficiency, and mass of isotope, so that the "y modes could be derived. The results obtained are sufficiently different from the coefficients routinely in use for them to affect significantly the results of assays performed on certain material streams. The measurements reported here have uncertainties, which are a factor of about two lower than those previously attained. 240Pu effective mass of 238Pu and 242Pu, 7238 and y242, play238Pu, 240Pu, and 242Pu enriched reference samples23g and 7242 coefficients for both counting