Abstract
Within the framework of the fission event generator FREYA, we are studying the sensitivity of various neutron observables to the yield distribution Y (A ,Z ,TKE) used as input to the code. Concentrating on spontaneous fission of 252 Cf, we have sampled a large number of different input yield functions based on χ2 fits to the experimental data on Y (A ) and Y (TKE|A ). For each of these input yield distributions, we then use FREYA to generate a large sample of complete fission events from which we extract a variety of neutron observables, including the multiplicity distribution, the associated correlation coefficients, and its factorial moments, the dependence of the mean neutron multiplicity on the total fragment kinetic energy TKE and on the fragment mass number A , the neutron energy spectrum, and the two-neutron angular correlation function. In this way, we can determine the variation of these observables resulting from the uncertainties in the experimental mesurements. The imposition of a constraint on the resulting mean neutron multiplicity reduces the variation of the calculated neutron observables and provides a means for shrinking the uncertainties associated with the measured data.
Highlights
Yield functionsWe wish to ascertain how sensitive important neutron observables are to the specified input yield function Y (A, Z , TKE)
We show here the effect on various neutron observables resulting from employing a sample of 1000 yield functions drawn from the distribution determined from available experimental data as described in Sect
By analyzing 106 complete fission events for each of the N =1000 yield functions, Y (n)( A, Z, TKE), n = 1, . . . , N, we determine the associated neutron multiplicity distribution, P(n)(ν), for which we have 1 = P(n)(ν), ν (n) = ν P(n)(ν) ν≥0 ν≥0 where ν (n) is the mean neutron multiplicity resulting from the particular yield function Y (n)( A, Z, TKE)
Summary
We wish to ascertain how sensitive important neutron observables are to the specified input yield function Y (A, Z , TKE). The general strategy is to consider an entire ensemble of possible yield functions that have been generated from the experimental data with due account taken of the associated uncertainties. In the present preliminary study, the adjustable FREYA parameters x, e0, dTKE, cS are kept constant at nominal values in order to bring out the effect of the variation in the input yield functions Y (A, Z , TKE). Three experiments had particular influence on the resulting distribution: Gook and Hambsch [12], Hambsch and Oberstedt [11], and Budtz-Jørgensen and Knitter [10] Those experiments provided all three quantities from the same data set. Each of the fragments undergo sequential neutron evaporation and the resulting product nuclei deexcite by photon radiation
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