Status of 252Cf anti ν and its impact on thermal reactor parameters

No discussion of nuclear reactor data problems would be complete without dealing with that most venerable of data discrepancies, anti ν for 252Cf. Anti ν, the number of neutrons produced in a fission event, is of commanding importance in the design and operation of any fission reactor. The neutron multiplicities of the fissile materials are commonly measured relative to anti ν for 252Cf, so the accuracy with which they are known cannot be greater than the accuracy with which anti ν for 252Cf is determined. Reactor designers have requested accuracies of 1/4% to 1/2% for the multiplicities. The existence of a spread of as much as 3% in the results from experiments claiming accuracies of the order of half a percent has represented a rather frustrating situation that was called a scandal by Herbert Kouts, keynoting the 1975 Nuclear Data Conference at Washington. A number of developments since then have helped to clarify the picture and make the discrepancies somewhat less scandalous than they then appeared to be. Nevertheless there continue to be some perplexing problems