[Mesa-users] about the decay rates of al26, al26-1 and al26-2

Meisel, Zach meisel at ohio.edu
Wed Feb 14 16:33:27 EST 2018


The REACLIB weak rates are just the terrestrial rates from Tuli’s Nuclear Wallet Cards. These aren’t suitable for astrophysical calculations involving high-temperature/high-density environments, since at high temperatures and densities, weak transitions can occur from thermally populated excited states, continuum electron-capture can happen, and all the good stuff Fuller, Fowler, and Newman discuss in their classic papers.  These un-measureable (or unmeasured, anyway) weak transition rates can be calculated using the shell model for the weak-transition matrix elements.

The most comprehensive weak rate library I’m aware of has been compiled by Chris Sullivan and collaborators: https://groups.nscl.msu.edu/charge_exchange/weakrates.html, which is described in a corresponding paper: http://iopscience.iop.org/article/10.3847/0004-637X/816/1/44.

My understanding from “star_job.defaults” is that the terrestrial rates from REACLIB are used for temperatures below 0.01GK for nuclei with Z<26  and for temperatures below 0.063GK if Z=>26.  At higher temperatures, the astrophysical weak rate tables are used. The tables in “weakreactions.tables” seem to be a blend of several different estimates, using shell-model where possible and the phenomenological FFN rates otherwise.  The weak rate library I link to above has similar sources  (I’m sure not by accident!).


Zach Meisel
Asst. Prof. of Physics & Astronomy
Ohio University
Email: meisel at ohio.edu
Web: http://inpp.ohiou.edu/~meisel

From: amber lauer via Mesa-users<mailto:mesa-users at lists.mesastar.org>
Sent: Wednesday, February 14, 2018 2:48 PM
To: Ertao Li<mailto:ertaolee at gmail.com>
Cc: let<mailto:let at szu.edu.cn>; mesa-users<mailto:mesa-users at lists.mesastar.org>
Subject: Re: [Mesa-users] about the decay rates of al26, al26-1 and al26-2

On Tue, Feb 6, 2018 at 9:31 AM, Ertao Li via Mesa-users <mesa-users at lists.mesastar.org<mailto:mesa-users at lists.mesastar.org>> wrote:
Dear all,

I am trying to do some research about the abundance of Al26 by using the MESA. I have some questions about the decay rates of al26, al26-1 and al26-2, because they confuse me. Can anyone help please?

Firstly, I noticed that the decay rates (stored in cache/*.bin) of  al26, al26-1 and al26-2 are constant and do come from $MESA/data/rates_data/JINA_reaclib***. But, from the MESA instruction paper  apj 220 (2015) 15, page 32:
\The rates module provides weak reaction rates for
\hundreds of isotopes. By default, when atoms are fully ionized,
\these rates are based (in order of precedence) on the tabulations
\of Langanke & Martínez-Pinedo...

What I think is that MESA only creates the decay rates from JINA but doesn't use them, MESA uses the  $MESA/data/rates_data/weakreactions.tables to get the decay rates but doesn't save them.  Am I correct?
Hi Ertao, did you ever get a response to this privately? Because I'm curious now too. I'm working on models which pull rates from a different, unsupported library, and my list includes (in a single list) both regular and weak rates. That leads me to believe it might be a similar case to the default, which pulls both from REACLIB, and according to this detail you've uncovered, probably overrides REACLIB's weak rates from those taken from these papers.

Also, does anyone know why these papers, which seem to employ shell model calculations, are favored over the accepted REACLIB rates, which do not?

Amber Lauer
Postdoctoral Researcher
Triangle University Nuclear Lab
Duke University
amber.lauer at tunl.duke.edu<mailto:amber.lauer at duke.edu>

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