A new study of 25Mg $(\alpha, n)$ 28Si angular distributions at $E_{\alpha} =3-5$ MeV

Abstract

The observation of 26Al gives us the proof of active nucleosynthesis in the Milky Way. However the identification of the main producers of 26Al is still a matter of debate. Many sites have been proposed, but our poor knowledge of the nuclear processes involved introduces high uncertainties. In particular, the limited accuracy on the 25Mg $(\alpha, n)$ 28Si reaction cross section has been identified as the main source of nuclear uncertainty in the production of 26Al in C/Ne explosive burning in massive stars, which has been suggested to be the main source of 26Al in the Galaxy. We studied this reaction through neutron spectroscopy at the CN Van de Graaff accelerator of the Legnaro National Laboratories. Thanks to this technique we are able to discriminate the $(\alpha, n)$ events from possible contamination arising from parasitic reactions. In particular, we measured the neutron angular distributions at 5 different beam energies (between 3 and 5 MeV) in the $17.5^{\circ}$ - $106^{\circ}$ laboratory system angular range. The presented results disagree with the assumptions introduced in the analysis of a previous experiment.