Using $(\alpha, xn)$ reaction rates and abundance ratios to constrain the weak $r$-process

Thanassis Psaltis (@psaltistha)
TU Darmstadt, Institut für Kernphysik Theoriezentrum

Based on A. Psaltis et al., Astrophys. J 935 27 (2022), arXiv: 2204.07136 [astro-ph]
Slides available at http://psaltisa.github.io/talks

How I see nuclear astrophysics


 

 

 

 

 

 

 
HD 122563 (DSS2/ Aladin Sky Atlas)

What do the old stars reveal to us?

See also: C. Sneden, J. J. Cowan and R. Gallino, Annu. Rev. Astron. Astrophys. 46, 241 (2008)
Talks by S. Goriely & G. Martínez-Pinedo • ⚠️ Solar r-process = Solar total - Solar s-process - Solar p-process

How many "r-processes" contribute to the production of elements between Sr and Ag?

Nucleosynthesis
in neutrino-driven ejecta

Image Credit: NASA/CXC/DSS/Rutgers/K.Eriksen et al.

How I see nuclear astrophysics

The weak $r$-process and the role $(\alpha, n)$ reactions

Take-home message #1


Elements between Sr and Ag can be produced in $\nu$-driven outflows via the weak $r$-process

What is the impact of the
$\mathbf{(\alpha,xn)}$ reactions
in the weak $r$-process?

How I see nuclear astrophysics

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

The $(\alpha,xn)$ reaction rates are sensitive to the $\alpha$-optical model potential and can differ by 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)

Enter the ATOMKI-v2 $\alpha$-nucleus potential

The rates are tabulated and available to the community ☺️
P. Mohr et al., At. Data Nucl. Data Tables 132, 101453 (2021)

How I see nuclear astrophysics

The framework of the impact study

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

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

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

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

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

  1. $\mathrm{^{84}Se}$, $\mathrm{^{87-89}Kr, ^{93}Sr}$
    Affect many elemental ratios in many astrophysical conditions

  2. $\mathrm{^{86}Br,^{86, 90}Kr, ^{87-89}Rb, ^{91, 92, 94}Sr, ^{94}Y}$
    Affect few elemental ratios in many astrophysical conditions

  3. $\mathrm{^{85}Se, ^{85}Br}$
    Affect many elemental ratios in few astrophysical conditions

  4. $\mathrm{^{63}Co, ^{67}Cu, ^{79, 81}Ga, ^{76}Zn, ^{80, 82}Ge, ^{83}As}$
    $\mathrm{^{87, 90, 91}Rb, ^{88-90}Sr, ^{95, 96}Y, ^{96-98}Zr}$
    Affect few elemental ratios in few astrophysical conditions

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

Take-home message #2


We combined observations, astrophysical modeling and nuclear theory
to study the impact of $(\alpha,xn)$ reactions to the weak $r$-process

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

How I see nuclear astrophysics

What has been done so far?

  • $\mathrm{^{86}Kr(\alpha,n)^{89}Sr}$, $\mathrm{^{96}Zr(\alpha,n)^{99}Mo}$ and $\mathrm{^{100}Mo(\alpha,n)^{103}Ru}$ at ATOMKI
    G.G. Kiss et al., Astrophys. J 908, 202 (2021) • T.N. Szegedi et al., Phys. Rev. C 104, 035804 (2021)
  • $\mathrm{^{75}Ga(\alpha,n)^{78}As}$, $\mathrm{^{85,86}Kr(\alpha,xn)}$, $\mathrm{^{85}Br(\alpha,xn)}$ at NSCL/FRIB (HabaNERO/SECAR)
    F. Montes, Z. Meisel et al.
  • $\mathrm{^{86}Kr(\alpha,n)^{89}Sr}$ and $\mathrm{^{94}Sr(\alpha,n)^{97}Zr}$ at TRIUMF (EMMA)
    C. Aa. Diget, A. M. Laird, M. Williams et al.
  • $\mathrm{^{86}Kr(\alpha,xn)^{89}Sr}$ and $\mathrm{^{100}Mo(\alpha,xn)^{103}Ru}$ at ANL/NSCL (MUSIC)
    M. L. Avila, J. Pereira et al.
    W. J. Ong et al., Phys. Rev. C 105, 055803 (2022)

First measurement of the $\boldsymbol{\mathrm{^{93}Sr}(\alpha,xn)\mathrm{^{96-x}Zr}}$ reaction

$\mathrm{^{93}Sr}(\alpha,xn)\mathrm{^{96}Zr}$ at Argonne with MUSIC

M. L. Avila et al., Nucl. Instrum. Methods Phys. Res A 859, 63 (2017)

  • Re-accelerated $\mathrm{^{93}Sr}$ beam from CARIBU.
  • Close to 100% efficiency.
  • Measure a large range of excitation functions of angle and energy integrated cross sections using single beam energy
Proposal #1923, PI: Psaltis, co-PI: Ong

Most of the rare isotope beams are accessible now!

FRIB PAC2 expected beam rates

What we expect in the near future

More observations of metal-poor stars and measurements on the key $(\alpha, xn)$ reactions will help us constrain the production site of the elements between Sr and Ag.

What about proton-rich ejecta?

Phys. Rev. Lett. (Accepted), arXiv: 2209.06465 [nucl-ex]
Phys. Rev. C (Accepted), arXiv: 2209.06472 [nucl-ex]

Acknowledgements

Almudena Arcones   Melina Avila   Camilla Juul Hansen   Max Jacobi   Zach Meisel   Peter Mohr   Fernando Montes   Wei Jia Ong   Hendrik Schatz

Take-home messages

  1. Elements between Sr and Ag can be produced
    in neutrino-driven outflows via the weak $r$-process.

  2. We combined observations, astrophysical modeling and nuclear theory
    to study the impact of $(\alpha,xn)$ reactions to the weak $r$-process.

  3. Future $(\alpha,xn)$ experiments using rare isotope beams (RIBs)
    will shed light on the production of elements between Sr and Ag.

Backup slides

The importance of the $(\alpha, n)$ reactions

$\mathrm{Timescale}: \frac{1}{\langle{\tau_x}\rangle} = \frac{\sum_{Z,A} \lambda_x(Z,A) Y(Z,A)}{\sum_{Z,A} Y(Z,A)}$

A. Arcones and G. Martinez-Pinedo, Phys. Rev. C 83, 045809 (2011) • J. Bliss et al., J. Phys. G 44, 054003 (2017)

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