LLNL-PRES This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract DE-AC52-07NA Lawrence Livermore National Security, LLC 14 th International Conference on Nuclear Reaction Mechanisms, Varenna, Italy June 15, 2015

Lawrence Livermore National Laboratory LLNL-PRES  Funding by DOE/SC/NP – Applications of Nuclear Science and Technology (ARRA) Partially supported by DOE/NNSA Office of Defense Nuclear Nonproliferation Research and Development  Anna Hayes (LANL), Co-PI  Andrii Chyzh (LLNL), most data analysis  Roger Henderson (LLNL), target fabrication  Collaborators: E. Kwan, J. Gostic (LLNL), J.L. Ullmann, A. Couture, T.A. Bredeweg, R.C. Haight, M. Jandel, H.Y. Lee, J. O’Donnell (LANL)

Lawrence Livermore National Laboratory LLNL-PRES  “Evidence for the stochastic aspect of prompt  emission in spontaneous fission”, PRC 85, 02160(R) (2012)  “Systematics of prompt  -ray emission in fission”, PRC 87, (2013)  “Total prompt  -ray emission in fission of 235 U, 239,241 Pu, and 252 Cf”, PRC 90, (2014)  “A compact gas-filled avalanche counter for DANCE”, NIM Phys. Res. A 694, 78 (2012)

Lawrence Livermore National Laboratory LLNL-PRES  Carried out in 2010 and 2011 at the Lujan Center of LANSCE using the DANCE array in conjunction with a parallel-plate avalanche counter (PPAC)  Prompt  ’s detected by DANCE in coincidence with the detection of fission fragments by PPAC for the neutron-induced fission in 235 U, 239,241 Pu with the E n from thermal to ~ 100 keV and the spontaneous fission in 252 Cf

Lawrence Livermore National Laboratory LLNL-PRES  DANCE (Detector for Advanced Neutron Capture Experiment) is highly segmented and highly efficient  -ray calorimeter, consisting of 160 BaF 2 scintillators of equal volume equal- solid angle coverage  PPAC designed jointly with LANL and fabricated in LLNL (Inclusive)(Fission)

Lawrence Livermore National Laboratory LLNL-PRES  Prompt  rays (E  ) 8 ns window set on the time spectrum between DANCE and PPAC  ray detected by the BaF 2 scintillator without any adjacent one triggered 235 U(n,f)  241 Pu(n,f)   Prompt total  energy (E , tot ) Summed energy of all  rays detected by DANCE within a time window of 40 ns  Prompt  multiplicity (M  ) Derived by combining adjacent scintillators if triggered

Lawrence Livermore National Laboratory LLNL-PRES  Nearly  -ray energy independence ( E  = 150 keV – 10 MeV) Multiplicity response Detection efficiency ( 85 – 88%) Peak-to-total ratio (~ 55%)  Unfolding possible One-dimension  -ray energy and multiplicity distribution (iterative Bayesian and singular value decomposition methods) Two-dimension total  -ray energy vs multiplicity distribution (iterative Bayesian method) Response matrix simulated numerically using GEANT4 (Measured) (Unfolded) 252 Cf (S.F.) (Brunson)

Lawrence Livermore National Laboratory LLNL-PRES  Results from both SVD and iterative Bayesian unfolding agree reasonably well  Comparison with earlier results Our measurements systematically lower than those of earlier ones by Verbinski (1973) for E   4 MeV (Measured) (Bayesian) (SVD) 235 U(n,f)  239 Pu(n,f)  (Verbinski)

Lawrence Livermore National Laboratory LLNL-PRES  Only iterative Bayesian method available  Each grid point in the response matrix is a two-dimension matrix of the same dimension Simulated numerically using GEANT4 Resulting ~ 3,300 such matrices for the response matrix Each matrix varied as a single entity during the iteration (5 MeV, 5) (8 MeV, 10) Multiplicity Total energy

Lawrence Livermore National Laboratory LLNL-PRES  Mean and width of the projections increases noticeably 235 U(n,f)  (Measured) (Unfolded) (Measured) (Unfolded)

Lawrence Livermore National Laboratory LLNL-PRES  M  has a greater mean value and a broader distribution as the Z number of the fissile nucleus increases  E , tot has no obvious systematic trend Nearly the same

Lawrence Livermore National Laboratory LLNL-PRES  ~ 5 – 7% difference between one and two-dimension unfolding  < 5% uncertainty for  M  and similar uncertainty assumed for the  E , tot   M  =  M  =  M  =  M  =

Lawrence Livermore National Laboratory LLNL-PRES  Current  E , tot  consistently higher than previous measurements by ~ 20% for all fissile nuclei studied  Current  M  consistently higher than previous measurements by ~ 10% except for the most recent ones Consistent with the evaluation made in ENDF/B-VII.1 [1] R. Billnert et al., PRC 87, (2013) [6] A. Oberstedt et al., PRC 87, (R) (2013) [21] T.E. Valentine, Ann. Nucl. Energy 28, 191 (2001) (MeV)

Lawrence Livermore National Laboratory LLNL-PRES  Systematics of the prompt  emission in fission for 235 U, 239,241 Pu, and 252 Cf has been studied using DANCE  The prompt E , tot vs M  was derived and unfolded to determine the physical one  The E , tot and M  distributions, projected from the 2-D spectrum, were measured for the first time  E , tot  is consistent with the value derived from a model-dependent analysis for 239 Pu [J. Ullmann et al., PRC 87, (2013)] However, they are about 20% higher than previous measured values using a single  -ray detector for all fissile nuclei studied ?  E ,tot  =  E     M  