Event-by-Event Fission Modeling
299
The parameters c and dTKE are strongly isotope dependent. In some cases, where
c is large, the neutron multiplicity is close to 2 and FREYA would produce a rather
narrow P (ν) without increasing c. Interestingly, the multiplicity distribution for
238 U(sf) is so narrow that it forces c < 1 in this case. The values of dTKE are
strongly correlated with c (positive correlation) as well as e 0 and c S (negative
correlation) because these parameters are more directly related to ν than x is since
changing x can change ν(A) while keeping ν fixed. See Ref. [6] for more details
and for comparison to data. This study is being followed by parameter optimization
for neutron-induced fission.
Acknowledgments The work of R.V. was performed under the auspices of the U.S. Department of
Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. The
work of J.R. and L.A.B. was performed under the auspices of the U.S. Department of Energy by
Lawrence Berkeley National Laboratory under Contract DE-AC02-05CH11231. This work was
supported by the Office of Defense Nuclear Nonproliferation Research & Development (DNN
R&D), National Nuclear Security Administration, U.S. Department of Energy.
References
1. R. Capote et al., RIPL – reference input parameter library for calculations of nuclear reactions
and nuclear data evaluations. Nucl. Data Sheets 110, 3107 (2009)
2. R. Vogt, J. Randrup, Improved modeling of photon observables with FREYA. Phys. Rev. C 96,
064620 (2017)
3. A. Obersted, et al.: Improved values for the characteristics of prompt-fission γ -ray spectra from
the reaction 235 U(n th ,f), Phys. Rev. C 87, 051602(R) (2013)
4. R. Vogt, J. Randrup, Neutron angular correlations in spontaneous and neutron-induced fission.
Phys. Rev. C 90, 064623 (2014)
5. R. Vogt, A. Nicholson, J. Randrup, I. Gauld, S. Croft, Uncertainty quantification with the eventby-event fission model FREYA, in Proceedings 1 st ANS Advances in Nuc. Nonpro. Tech. and
Policy, Santa Fe, NM (2016). Technical Report: LLNL-CONF-690741
6. J. Van Dyke, L.A. Bernstein, R. Vogt, Parameter optimization and uncertainty analysis of FREYA
for spontaneous fission (2018). arXiv:1809.05587
7. S. Kirkpatrick, C.D. Gelatt, M.P. Vecchi, Optimization by simulated annealing. Science 220,
4598 (1983)
8. P. Santi, M. Miller, Reevaluation of prompt neutron emission multiplicity distributions for
spontaneous fission. Nucl. Sci. Eng. 160, 190 (2008)
299
The parameters c and dTKE are strongly isotope dependent. In some cases, where
c is large, the neutron multiplicity is close to 2 and FREYA would produce a rather
narrow P (ν) without increasing c. Interestingly, the multiplicity distribution for
238 U(sf) is so narrow that it forces c < 1 in this case. The values of dTKE are
strongly correlated with c (positive correlation) as well as e 0 and c S (negative
correlation) because these parameters are more directly related to ν than x is since
changing x can change ν(A) while keeping ν fixed. See Ref. [6] for more details
and for comparison to data. This study is being followed by parameter optimization
for neutron-induced fission.
Acknowledgments The work of R.V. was performed under the auspices of the U.S. Department of
Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. The
work of J.R. and L.A.B. was performed under the auspices of the U.S. Department of Energy by
Lawrence Berkeley National Laboratory under Contract DE-AC02-05CH11231. This work was
supported by the Office of Defense Nuclear Nonproliferation Research & Development (DNN
R&D), National Nuclear Security Administration, U.S. Department of Energy.
References
1. R. Capote et al., RIPL – reference input parameter library for calculations of nuclear reactions
and nuclear data evaluations. Nucl. Data Sheets 110, 3107 (2009)
2. R. Vogt, J. Randrup, Improved modeling of photon observables with FREYA. Phys. Rev. C 96,
064620 (2017)
3. A. Obersted, et al.: Improved values for the characteristics of prompt-fission γ -ray spectra from
the reaction 235 U(n th ,f), Phys. Rev. C 87, 051602(R) (2013)
4. R. Vogt, J. Randrup, Neutron angular correlations in spontaneous and neutron-induced fission.
Phys. Rev. C 90, 064623 (2014)
5. R. Vogt, A. Nicholson, J. Randrup, I. Gauld, S. Croft, Uncertainty quantification with the eventby-event fission model FREYA, in Proceedings 1 st ANS Advances in Nuc. Nonpro. Tech. and
Policy, Santa Fe, NM (2016). Technical Report: LLNL-CONF-690741
6. J. Van Dyke, L.A. Bernstein, R. Vogt, Parameter optimization and uncertainty analysis of FREYA
for spontaneous fission (2018). arXiv:1809.05587
7. S. Kirkpatrick, C.D. Gelatt, M.P. Vecchi, Optimization by simulated annealing. Science 220,
4598 (1983)
8. P. Santi, M. Miller, Reevaluation of prompt neutron emission multiplicity distributions for
spontaneous fission. Nucl. Sci. Eng. 160, 190 (2008)