Fission in the $r$-process


Matthew Mumpower

Frontiers (2019)

Wednesday May 22$^{nd}$ 2019

FIRE Collaboration
Fission In R-process Elements

Nuclear physics as the language of the $r$-process

1st order: masses, $\beta$-decay rates, capture rates & fission

Dillmann et al. EPJA (2002) • Aprahamian et al. (2018) • See review paper: Mumpower et al. PPNP 86 (2016)

Much will be measured at FRIB

But fission studies will remain relatively inaccessible

∴ Fission theory is critical find any sort of "smoking gun" of heavy element production

Spyrou et al. PRL (2016) • Vilen et al. • PRL (2018) Orford et al. PRL (2018) • Sprouse et al. (2019) • Figure by Mumpower

Nuclear fission in a nutshell

The fission process:

A heavy nucleus splits into two lighter fragments

Subsequent particle emission and decays then occur

Many events gives rise to fission yield

Meitner & Frisch (1938) • Bohr & Wheeler (1939) • Figure from Verriere & Mumpower in prep. (2019)

Nuclear fission for the $r$-process

Influence on the $r$-process:

Fission rates and branching determine re-cycling (robustness)

Fragment yields place material at lower mass number; barriers determine hot spots

Large Q-value ⇒ impacts thermalization and therefore possibly observations

Responsible for what is left in the heavy mass region when nucleosynthesis is complete ⇒ "smoking gun"

Holmbeck et al. ApJ 870 1 (2019) • Vassh et al. J. Phys. G (2019) • Figure from Verriere & Mumpower in prep. (2019)

Long-lived actinides

Recent calculations show: if actinides are produced, they are usually overproduced versus lanthanides

A sufficient amount of dilution with lighter $r$-process material is required to match the solar isotopic residuals

∴ Fission theory can also inform us on galactic chemical evolution

Côté et al. ApJ (2018) • Holmbeck et al. ApJ 870 1 (2019) • Vassh et al. J. Phys. G (2019) • Holmbeck et al. submitted (2019)

One example: $^{254}$Cf(Z=98)

Is there any possible precursor to show that actinide nucleosynthesis has occurred in an event?... Maybe!

The spontaneous fission of $^{254}$Cf can be a primary contributor to nuclear heating at late-time epochs

The $T_{1/2}\sim 60$ days; found from nuclear weapons testing

Baade et al. PASP (1956) • Conway et al. JOSA (1962) • Y. Zhu et al. ApJL 863 2 (2018) • Vassh et al. J. Phys. G (2019)

Observational Impact of Californium

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

This also has implications for merger morphology...

Y. Zhu et al. ApJL 863 2 (2018) • Miller et al. in prep (2019) • Korobkin et al. in prep (2019)

Calculated yield (Californium)

Jaffke et al. PRC 67 034608 (2018) • Y. Zhu et al. ApJL 863 2 (2018) • Mumpower et al. in prep. (2019)

Special thanks to

My collaborators

A. Aprahamian, J. Barnes, B. Côté, J. Clark, C. Fryer, E. Holmbeck, A. Hungerford, P. Jaffke, T. Kawano, O. Korobkin, S. Liddick, G. C. McLaughlin, J. Miller, P. Möller, R. Orford, J. Randrup, G. Savard, A. Sierk, N. Schunck, T. Sprouse, A. Spyrou, I. Stetcu, R. Surman, P. Talou, N. Vassh, M. Verriere, R. Vogt, Y. Zhu
& many more...

Students Postdocs FIRE LANL


The $r$-process relies on fission in many ways:

Re-cycling materialActinide productionLate-time observations

FRIB and other facilities will make a lot of measurements, but fission studies remain relatively inaccessible

Fission theory is crucial to understanding the formation of the heaviest elements (and $A\sim130$)

The FIRE Collaboration will soon provide a suite of new fission properties for the community:

Rates • Branchings • Yields • Q-values • Spectra

Results / Data / Papers @