Simultaneous calculation of fission fragment charge and mass yields with the eFRLDM

        LA-UR-21-30063

Matthew Mumpower

Fall DNP

Wednesday Oct. 13$^{th}$ 2021


Nuclear Data Team
Theoretical Division

Los Alamos National Laboratory Caveat

The submitted materials have been authored by an employee or employees of Triad National Security, LLC (Triad) under contract with the U.S. Department of Energy/National Nuclear Security Administration (DOE/NNSA).

Accordingly, the U.S. Government retains an irrevocable, nonexclusive, royaltyfree license to publish, translate, reproduce, use, or dispose of the published form of the work and to authorize others to do the same for U.S. Government purposes.

Why do we need fission yields?

Fission yields are needed for a variety of modern applications

Industrial applications: simulation of reactors, fuel cycles, waste management

Experiments: backgrounds, isotope production with radioactive ion beams (fragmentation)

Science applications: nucleosynthesis, light curve observations

Other Applications: national security, nonproliferation, nuclear forensics

Figure: Chi-Nu detector (left), Reactor cooling towers (middle), Neutron star merger (right)

A basic picture of fission

Follow progression of the nucleus from compact to highly elongated shapes

Randrup et al. PRL (2011) • Randrup et al. PRC (2011) • Randrup et al. PRC (2013) • Figure from Mumpower et al. PRC 101 054607 (2020)

Fragment yield calculation (FRLDM)

Ensemble of fission events leads to the cumulation of the yield curve ($^{235}$U + n$_{\rm{therm}}$)

Relies on geometric splitting argument for the scission configuration

Mumpower et al. PRC 101 054607 (2020)

Mass and charge yields both well reproduced

However! We could not simultaneously predict both...

Mumpower et al. PRC 101 054607 (2020)

Updates to our model (eFRLDM)

Higher resolution of Harmonic Oscillator basis

Improved treatment of the Strutinsky procedure

New Potential Energy Surfaces (PES) on a finer-grained, larger grid

New technique for obtaining fission yields in the limit of overdamped motion

Consequences

M. Verriere: first theoretical prediction of odd-even staggering using a particle number projection technique

We also obtain the charge polarization of the nascent fragment distributions in agreement with experiment

Verriere et al. PRC 100 024612 (2019) • Verriere & Mumpower PRC 103 034617 (2020)

eFRLDM Results: $^{235}$U + n$_{\rm{therm}}$

We can now describe Y(A), Y(Z) and Y(Z,A) simultaneously

Verriere et al. PRC 100 024612 (2019) • Verriere & Mumpower PRC 103 034617 (2020)

eFRLDM Results: $^{235}$U + n$_{\rm{therm}}$

Fragment yields no longer follow unchanged charge distribution (UCD) assumption (Blacked dashed line)

Verriere et al. PRC 100 024612 (2019) • Verriere & Mumpower PRC 103 034617 (2020)

eFRLDM Results: $^{235}$U + n$_{\rm{therm}}$

Charge polarization offset predicted and in agreement with experimental measurements (red lines)

Verriere et al. PRC 100 024612 (2019) • Verriere & Mumpower PRC 103 034617 (2020)

Odd-even staggering in charge yields

For the reactions ($^{233}$U + n$_{\rm{therm}}$) [left] and ($^{235}$U + n$_{\rm{therm}}$) [right]

First theoretical prediction of odd-even staggering using a particle number projection technique

Verriere et al. PRC 100 024612 (2019) • Verriere & Mumpower PRC 103 034617 (2020)

Special thanks to

My collaborators

P. Jaffke, T. Kawano, J. Randrup, N. Schunck, T. Sprouse, I. Stetcu & M. Verriere

Postdoc

Summary

Many modern applications require a deep understanding of fission

We have enhanced the FRLDM model to describe:

simultaneous fragment yieldscharge polarizationodd-even staggering in charge yields

FRIB, etc. will help to constrain nuclear models, but the heaviest elements will remain relatively inaccessible

We therefore need to keep developing and studying theoretical models of nuclear physics, especially fission

Future upgrades to this type of fission modeling are in the works!

Results / Data / Papers @ MatthewMumpower.com