Speaker
Joseph Frost-Schenk
(University of York)
Description
15N(α,γ)19F is known to be one of the key formation mechanisms of 19F in AGB stars [1]. 19F may also be produced through this reaction in other stars such as Wolf-Rayet stars [2]. The 19F abundance observed in the stellar spectra strongly depends on the conditions in the astrophysical site. Its nucleosynthetic origin has been debated for several decades, however the understanding of the 15N(α,γ)19F reaction rate within the Gamow window at 200 MK for AGB stars is incomplete. Discrepancies in strength and energy exist between previous measurements in one of the key resonances, at Ec.m.=1.323 MeV. Furthermore, the direct-capture, non-resonant cross-section has never been directly measured.
The DRAGON recoil separator at TRIUMF was utilised to perform an inverse kinematics measurement of the 15N(α,γ)19F reaction. Recoiling 19F nuclei leaving the windowless helium gas target were separated using DRAGON’s electromagnetic mass separator and detected in a DSSSD. Emitted gamma-rays from the de-excitation of the compound nucleus were detected in a BGO array surrounding the target and used for a coincidence analysis. We have measured the strength and energy of the Ec.m.=1.323MeV resonance in the 15N(α,γ)19F reaction as well as the direct-capture cross section down to an energy of Ec.m.=0.96 MeV. The 2017 ERNA measurement by Di Leva et al. [3] was the first time 15N(α,γ)19F was measured in inverse kinematics; two strong reference resonances were measured. This measurement at DRAGON is the second inverse kinematics measurement. Our new measurement of the Ec.m.=1.323MeV resonance will help in solving the existing discrepancies regarding its strength, and provides an independent measurement of its energy, as well as the first measurement of the direct-capture contribution in the low-energy regime. This measurement will reduce uncertainties in 15N(α,γ)19F reaction rate, especially in the direct-capture component where no previous measurements exist, thus helping to refine our understanding of AGB models and 19F production.
References
[1] O. Staneiro et al., The Astrophysical Journal. 785 (2014) 77.
[2] G. Meynet and M.Arnould, A& A. 335 (2000) 176.
[3] A. Di Leva et al., Phys. Rev. C. 95 (2017) 045803.
Primary authors
Annika Lennarz
(TRIUMF)
Joseph Frost-Schenk
(University of York)
Co-authors
Dr
Alison Laird
(University of York)
Mr
Athanasios Psaltis
(McMaster University)
Barry Davids
(TRIUMF)
Dr
Chris Ruiz
(TRIUMF)
Dr
Christian Aaen Diget
(University of York)
Prof.
Daniel Bardayan
(University of Notre Dame)
Mr
Daniel Golton
(University of York)
Dave Hutcheon
(TRIUMF)
Dr
Devin Connolly
(TRIUMF)
Drew Blankstein
(University of Notre Dame)
J Karpesky
(Colorado School of Mines)
Johnson Liang
(McMaster University)
M Lovely
(Colorado School of Mines)
Matthew Hall
(University of Notre Dame)
Mr
Matthew Williams
(University of York)
Peter Machule
(TRIUMF)
Dr
Simon Fox
(University of York)
Dr
Stephen Gillespie
(TRIUMF)
Uwe Greife
(Colorado School of Mines)
