LLNL-PRES-672063This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract

DE-AC52-07NA27344. Lawrence Livermore National Security, LLC

Prompt emission in fission of235U, 239,241Pu, and 252Cf

14th International Conference on Nuclear Reaction Mechanisms, Varenna, Italy

Ching-Yen Wu

June 15, 2015

Lawrence Livermore National Laboratory LLNL-PRES-6720632

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)

Acknowledgement

Lawrence Livermore National Laboratory LLNL-PRES-6720633

“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,

034620 (2013)

“Total prompt -ray emission in fission of 235U, 239,241Pu, and 252Cf”, PRC 90, 014602 (2014)

“A compact gas-filled avalanche counter for DANCE”, NIM

Phys. Res. A 694, 78 (2012)

Presentation based on

Lawrence Livermore National Laboratory LLNL-PRES-6720634

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)

Experiments

Prompt ’s detected by DANCE

in coincidence with the detection

of fission fragments by PPAC for

the neutron-induced fission in 235U, 239,241Pu with the En from

thermal to ~ 100 keV and the

spontaneous fission in 252Cf

Lawrence Livermore National Laboratory LLNL-PRES-6720635

DANCE (Detector for Advanced Neutron Capture Experiment) is highly segmented and highly efficient -ray calorimeter, consisting of 160 BaF2 scintillators of equal volume equal-solid angle coverage

PPAC designed jointly with LANL and fabricated in LLNL

Equipment

(Inclusive) (Fission)

Lawrence Livermore National Laboratory LLNL-PRES-6720636

Definition Prompt rays (E)

• 8 ns window set on the time

spectrum between DANCE and

PPAC

• ray detected by the BaF2 scintillator

without any adjacent one triggered

235U(n,f)

241Pu(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-6720637

Uniqueness 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)

252Cf (S.F.)

(Brunson)

Lawrence Livermore National Laboratory LLNL-PRES-6720638

One-dimension unfolding: E 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)

235U(n,f)

235U(n,f) 239Pu(n,f)

(Verbinski)(Verbinski)

Lawrence Livermore National Laboratory LLNL-PRES-6720639

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

Two-dimension unfolding: E,tot vs M

(5 MeV, 5) (8 MeV, 10)

Mult

iplici

ty

Total energy

Lawrence Livermore National Laboratory LLNL-PRES-67206310

Mean and width of the projections increases noticeably

Two-dimension unfolding: E,tot vs M235U(n,f)

(Measured)

(Unfolded)

(Measured)

(Unfolded)

Lawrence Livermore National Laboratory LLNL-PRES-67206311

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

Comparison of E,tot and M

Lawrence Livermore National Laboratory LLNL-PRES-67206312

~ 5 – 7% difference between one and two-dimension unfolding

< 5% uncertainty for M and similar uncertainty assumed for the

E,tot

Uncertainty

M = 6.95 7.35

M = 7.50 7.93

M = 7.50 7.97

M = 8.16 8.75

Lawrence Livermore National Laboratory LLNL-PRES-67206313

Comparison of mean E,tot and M

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, 024601 (2013) [6] A. Oberstedt et al., PRC 87, 051602(R) (2013)[21] T.E. Valentine, Ann. Nucl. Energy 28, 191 (2001)

(MeV)

Lawrence Livermore National Laboratory LLNL-PRES-67206314

Summary Systematics of the prompt emission in fission for 235U, 239,241Pu,

and 252Cf 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 239Pu [J. Ullmann et al., PRC 87, 044607 (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