Speaker
Mr
Nicolas Hubbard
(University of York and Aarhus University)
Description
The
23 Na(α,p) 26 Mg reaction has been identified as having a significant impact on the nucleo-
synthesis of elements, such as
23 Na [1] and 26 Al [2], in massive stars, and of light isotopes in
type-Ia supernovae [3]. We will present new experimental results, as well as a combined reaction
rate based on all available data, and an assessment of its astrophysical impact on massive stars
and type-Ia supernovae.
Until 2014 this reaction was only measured in experiments which suffered from normalisation
issues. Accordingly, reaction rate compilations such as REACLIB preferred Hauser-Feshbach
statistical reaction rates, whose uncertainty may be greater than a factor of 3 for alpha-induced
reactions. These uncertainties may be further compounded by the relatively light nuclei involved,
where the level density is low. An improved experimental measurement was therefore suggested
in reference [2]. Since 2014 there have been several measurements of the reaction utilising various
new techniques to avoid the earlier experimental issues [4 – 8]. All of the experiments have found
results consistent with one another, as well as with Hauser-Feshbach predictions in the energy
range E cm = 1.7 − 3.0 MeV.
We have directly measured new angular distributions using the setup in reference [5] and
have corrected the data in references [4, 6] based on these angular distributions, in order to
reduce their systematic uncertainty. From these corrected data we calculate a new, combined,
experimental reaction rate. We have then implemented this reaction rate into astrophysical
models of massive stars and type-Ia supernovae to identify its impact on the nucleosynthesis of
key isotopes, and from these provide improved constraints on abundances. These constraints
may help to identify the primary astrophysical site of
26 Al production.
The impact of this new experimental rate on hydrostatic shell burning in massive stars,
explosive burning in massive stars, and type-Ia supernovae was determined using the nuclear
post-processing codes ppn [9] and a delayed detonation model reference [10]. The change in
abundance of isotopes in the region of A = 20 − 30 was calculated and compared to REACLIB
reaction rates, along with the uncertainty in isotopic abundances. The impact of these results
on galactic
23 Na and 26 Al production will be discussed.
Primary author
Mr
Nicolas Hubbard
(University of York and Aarhus University)
