LA-UR-18-26590

Los Alamos National Lab

*ARIEL Workshop*

Wed. July 18$^{th}$ 2018

FIRE Collaboration

Fission In R-process Elements

Mass of around 1.1 to 3 M$_\odot$

Density $10^{9}$ to $10^{17}$ kg/m$^{3}$

Magnetic field $10^{10}$ Tesla

Color depends on equation of state...

GW170817 - named for the day it was discovered

NGC 4993 - about 40 Mpc away

Important for GCE

Coalescence time: ~1 million years

Chirp mass $\sim 1.188$

implies NS binary

Why was GW170817 so bright?

What is the morphology of the remnant?

What is the typical timescale for the merger? (statistics)

What are the properties of the equation of state?

What is the tidal deformability?

What role can neutrinos play?

How much material can be ejected?

What heavy elements can be created?

We want to describe the abundances observed in nature

But there is uncertainty in:

The astrophysical conditions

The nuclear physics inputs

Both are required to model the nucleosynthesis

**1st order:** masses, $\beta$-decay rates, reaction rates & branching ratios

See review paper: **Mumpower** *et al.* PPNP 86 (2016)

Nuclear physics inputs are critical in determining the resultant nucleosynthesis that occurs in astrophysical environments.

Fission properties in particular are difficult to measure as well as model.

At Los Alamos we have focused on describing:

neutron-induced fission, $\beta$-delayed fission & fission yields.

Our results are based off the FRDM and FRLDM models.

Möller *et al.* ADNDT (2018) • Cote *et al.* ApJ 855 2 (2018) • **Mumpower** *et al.* PPNP 86 (2016)

Schematic fission process

for $\beta$-delayed neutron emission & fission

Motivation: We want to describe the neutron,$\gamma$ & fission competition during de-excitation

We combine both Quasi-particle Random Phase Approximation (QRPA) and Hauser-Feshbach (HF) theory.

This will allow for the calculation of ground state production probabilities, particle multiplicity and particle spectra.

To do this we make use of the Bohr independence hypothesis of compound nucleus formation

Benchmarking: 9% global model uncertainty to measured $P_{1n}$ values

__The best in the business!__

Wu

We have extended the model to describe $\beta$-delayed fission ($\beta$df)

Simplification: one dimensional barrier penetration

Assumes a Hill-Wheeler form for fission transmission

Near the dripline $Q_{beta}$ ⇡ $S_{n}$ ⇣

Multi-chance $\beta$df: *each* daughter may fission

The yields in this decay mode are a convolution of many fission yields!

$\beta$df occupies a large amount of real estate in the NZ-plane

Multi-chance $\beta$df outlined in black

Network calculation of neutron star merger tidal ejecta

$\beta$df alone prevents the production of superheavy elements in nature

Network calculation of neutron star merger ejecta; FRDM2012 inputs

$\beta$df can shape the final pattern near the $A=130$ peak

Network calculation of neutron star merger ejecta; FRDM2012 inputs

Multi-chance $\beta$df contributes at both early and late times

Network calculation of neutron star merger ejecta; FRDM2012 inputs

$\beta$df overtakes (n,f) during the decay back to stability

High thermalization efficiency and large Q-value ↦ influential for the radioactive decay powering the kilonova

The spontaneous fission of $^{254}$Cf __ primary__ contributor to nuclear heating at late-time epochs

The $T_{1/2}\sim 60$ days but yield distribution is not known

Y. Zhu *et al.* [accepted ApJL] arXiv:1806.09724 (2018)

P. Jaffke *et al.* in prep. • Y. Zhu *et al.* [accepted ApJL] arXiv:1806.09724 (2018)

The feeding of $^{254}$Cf is primarily through $\beta$-decay.

Alpha feeding is blocked via $^{258}$Fm spontaneous fission.

Y. Zhu *et al.* [accepted ApJL] arXiv:1806.09724 (2018)

Both near- and middle- IR are impacted by the presence of $^{254}$Cf

Late-time epoch brightness can be used as a proxy for actinide nucleosynthesis

Future JWST will be detectable out to 250 days with the presence of $^{254}$Cf

Y. Zhu *et al.* [accepted ApJL] arXiv:1806.09724 (2018)

My collaborators

J. Barnes, A. J. Couture, W. P Even, C. F. Fryer, E. Holmbeck, P. Jaffke, T. Kawano, O. Korobkin, G. C. McLaughlin, P. Möller, T. Sprouse, R. Surman, N. Vassh, M. Verriere & Y. Zhu

▣ Students ▣ Postdocs

LANL has made recent progress in describing

neutron-induced fission • $\beta$-delayed fission • fission yields

These properties substantially influence nucleosynthetic yields

The production of $^{254}$Cf is important for late-time kilonova observations and is tied to the morphology of the ejecta

Impact of FRLDM yields to be explored in the future

Results at MatthewMumpower.com