# Ages and cosmochronometry¶

$$t = 46.67~\text{Gyr} \left[\log\epsilon\left(\text{Th/Eu}\right)_0 - \log\epsilon\left(\text{Th/Eu}\right)_{\text{obs}}\right]$$
$$t = 14.84~\text{Gyr} \left[\log\epsilon\left(\text{U/Eu}\right)_0 - \log\epsilon\left(\text{U/Eu}\right)_{\text{obs}}\right]$$
$$t = 21.80~\text{Gyr} \left[\log\epsilon\left(\text{U/Th}\right)_0 - \log\epsilon\left(\text{U/Th}\right)_{\text{obs}}\right]$$

# Can varying levels of neutron richness in a NSM account for the actinide boost?

M. Mumpower and T. Sprouse

Low-entropy dynamical (tidal) ejecta of a NSM
(Korobkin+ 2012; Rosswog+ 2013)

Vary the initial electron fraction: $Y_e=0.005 - 0.250$

$Y_e = \left[1+(n/p)\right]^{-1}$

# Ages and cosmochronometry¶

$$t = 46.67~\text{Gyr} \left[\log\epsilon\left(\text{Th/Eu}\right)_0 - \log\epsilon\left(\text{Th/Eu}\right)_{\text{obs}}\right]$$
$$t = 14.84~\text{Gyr} \left[\log\epsilon\left(\text{U/Eu}\right)_0 - \log\epsilon\left(\text{U/Eu}\right)_{\text{obs}}\right]$$
$$t = 21.80~\text{Gyr} \left[\log\epsilon\left(\text{U/Th}\right)_0 - \log\epsilon\left(\text{U/Th}\right)_{\text{obs}}\right]$$

# Actinides are currently not observed at such high levels

Need a method to dilute the actinides to reduce the Th/Eu production ratio

# Actinide-Dilution model¶

## Distribution of $Y_e$¶

Tidal ejecta
($Y_e\approx 0.16$, Bovard+ 2017)

Disk wind
($Y_e\approx 0.22$; Lippuner+ 2017)

$m_{\rm wind}/m_{\rm dyn}= 3$
from estimates of GW170817
(Rosswog+ 2017; Tanaka+ 2017)

# Actinide-Dilution with Matching model¶

Builds empircal mass ejecta distributions as a function of $Y_e$ (0.005-0.450)

To explain entire pattern from Zr to U

# Summary and Outlook¶

The actinides are over-produced in very cold, neutron-rich (tidal) ejecta

NSMs could still be an actinide-boost source if most of the ejecta mass does not contribute actinides

The same r-process source can in principle account for observed actinide variations

How do the empirically built ejecta distributions compare to NSM simulations?

Entropy, dynamical timescale, nuclear physics variations...

# Special Thanks¶

Rebecca Surman (ND), Nicole Vassh (ND), Matthew Mumpower (LANL), Trevor M. Sprouse (ND)
Gail C. McLaughlin (NC State), Anna Frebel (MIT)

Timothy C. Beers (ND), Terese T. Hansen (TAMU), Chris Sneden (UT-Austin), Vinicius M. Placco (ND),
Ian U. Roederer (UMich.), Charli M. Sakari (UW), Rana Ezzeddine (MIT)
Grant Mathews (ND), Ani Aprahamian (ND), Toshihiko Kawano (LANL)