Exploring the Origin of Light Heavy Elements

using experiments, theory, and observations

 

Thanassis Psaltis
Triangle Universities Nuclear Laboratory
psaltis.tha@duke.edu
 

January 11, 2024
ATOMKI


 

Image Credit: NASA/CXC/SAO

Acknowledgements


Almudena Arcones   Melina Avila   Camilla Juul Hansen   Gábor Kiss  

Peter Mohr   Fernando Montes   Wei Jia Ong Hendrik Schatz


What is the origin of the elements?

C. Kobayashi, A. Karakas and M. Lugaro, Astrophys. J 900, 179 (2020)

 

 

 

 

 

 

 

HD 122563 (DSS2/ Aladin Sky Atlas)

What do the ancient stars show us?


See also: C. Sneden, J. J. Cowan and R. Gallino, Annu. Rev. Astron. Astrophys. 46, 241 (2008)

How many processes contribute to the production of elements between
strontium and silver?

What is the origin of the elements?

C. Kobayashi, A. Karakas and M. Lugaro, Astrophys. J 900, 179 (2020)

The weak $r$-process

  • Where?

    In neutrino-driven outflows of explosive environments (ccSNe or NSMs)

  • When?

    During the expansion of the hot and dense outflows ($Y_e \equiv n_p/(n_p+n_n),s,\tau$)

  • How?

    After an $\alpha$-rich freeze-out from NSE at T= 5-2 GK $(\alpha,n)$ reactions produce heavy elements

  • What?

    Can synthesize heavy elements around Z = 47 (silver) found in metal-poor stars

S. Woosley & R.D. Hoffman, Astrophys. J 395, 202 (1992) • S. Wanajo et al., Astrophys. J. 554, 578 (2001) • A. Arcones & F. Montes, Astrophys. J 731, 5 (2011)

How important are the $\mathbf{(\alpha,xn)}$ reactions in the weak $r$-process?

How much do we know the $(\alpha,xn)$ reaction rates?

The $(\alpha,xn)$ reaction rates are sensitive to the $\alpha$-nucleus potential
and their uncertainties can be up to two orders of magnitude.


 
J. Pereira and F. Montes, Phys. Rev. C 93, 034611 (2016) • P. Mohr, Phys. Rev. C 94, 35801 (2016)

Framework of the sensitivity study

A. Parikh et al., Astrophys. J., Suppl. Ser. 178, 110 (2008)
N. Nishimura et al., Mon. Not. R. Astron. Soc 489, 1379 (2019)
J. Bliss et al., Phys. Rev. C 101, 055807 (2020)
P.A. Denissenkov et al., Mon. Not. R. Astron. Soc 503, 3913 (2021)
  • Relevant thermodynamic profiles spanning the astrophysical phase-space ($Y_e$, $s$, $\tau$)
    J. Bliss et al., Astrophys. J 855, 135 (2018)

  • $(\alpha, xn)$ reaction rates based on the Atomki-v2 $\alpha$-nucleus potential
    P. Mohr et al., At. Data Nucl. Data Tables 132, 101453 (2021)
  • MC sampling of the $(\alpha,xn)$ reaction rates (104 calculations)

  • Find the most impactful $(\alpha,xn)$ reactions and compare with observations
For more details: A. Psaltis et al., Astrophys. J 935, 27 (2022)

The impact of updated $(\alpha,n)$ reaction rates to elemental abundances

Same model, but different $(\alpha, xn)$ reaction rates!

A. Psaltis et al., Astrophys. J 935, 27 (2022)

The impact of new $(\alpha,n)$ reaction rates to elemental abundance ratios

A. Psaltis et al., Astrophys. J 935, 27 (2022)

Combine observations, astrophysical modeling and nuclear physics uncertainties

Which are the most important $\mathbf{(\alpha,xn)}$ reactions for the weak $r$-process?

Finding the most important $(\alpha,n)$ reactions for the weak $r$-process

Search for the (anti)correlations! 🔍

The most important $(\alpha,n)$ reactions for the weak $r$-process

N=50 shell closure is a bottleneck for T= 4-5 GK due to the $(n,\gamma) \leftrightarrow (\gamma,n)$ equilibrium

Can we study the most important
$\mathbf{(\alpha,xn)}$ reactions in the lab?

Most of the relevant beams are accessible!


Expected FRIB ultimate beam rates

What has been measured so far?

  • $\mathrm{^{86}Kr(\alpha,n)}$, $\mathrm{^{96}Zr(\alpha,n)}$ and $\mathrm{^{100}Mo(\alpha,n)}$ at ATOMKI
    G.G. Kiss et al., Astrophys. J 908, 202 (2021) • T.N. Szegedi et al., Phys. Rev. C 104, 035804 (2021)

  • $\mathrm{^{75}Ga(\alpha,n)}$, $\mathrm{^{85,86}Kr(\alpha,xn)}$, $\mathrm{^{85}Br(\alpha,xn)}$ at NSCL/FRIB (HabaNERO/SECAR)
    F. Montes, J. Pereira et al.

  • $\mathrm{^{86}Kr(\alpha,xn)}$, $\mathrm{^{87}Rb(\alpha,xn)}$, $\mathrm{^{88}Sr(\alpha,xn)}$, $\mathrm{^{100}Mo(\alpha,xn)}$ at Argonne (MUSIC)
    M. L. Avila, C. Fougères et al.
    W. J. Ong et al., Phys. Rev. C 105, 055803 (2022)

  • $\mathrm{^{86}Kr(\alpha,n)}$ and $\mathrm{^{94}Sr(\alpha,n)}$ at TRIUMF (EMMA)
    C. Aa. Diget, A. M. Laird, M. Williams et al.
    C. Angus et al., EPJ Web of Conferences, NPA-X (2023)

First measurement of the $\boldsymbol{\mathrm{^{93}Sr}(\alpha,xn)}$ reaction at Argonne with MUSIC



Proposal #1923, PI: A. Psaltis, co-PI: W.J. Ong

$\mathrm{^{93}Sr}(\alpha,xn)$ at Argonne with MUSIC

M. L. Avila et al., NIM A 859, 63 (2017)

  • Re-accelerated $\mathrm{^{93}Sr}$ beam from $\nu$CARIBU.

  • MUSIC has close to 100% efficiency due to its segmented anode structure.

  • Use a single beam energy to measure a large range of excitation functions of angle integrated cross sections.

What is on the horizon?


New experimental measurements of the key $(\alpha, xn)$ reactions and multi-messenger observations will help us constrain the contribution of neutrino-driven outflows to the production elements between strontium and silver.

Summary

  1. The weak $r$-process in neutrino-driven outflows can contribute to the production of elements between strontium and silver that are observed in Galactic metal-poor stars.

  2. We explored the impact of $(\alpha,xn)$ reactions to the weak $r$-process and identified the most important of them to motivate future experiments in stable and radioactive ion beam facilities.

  3. Experiments in the current and next-generation stable and RIB facilities, multimessenger observations and theoretical modeling will enhance our understanding of the origin of the light heavy elements.

Köszönöm!

Slides available at http://psaltisa.github.io/talks