The production of 26 Al in massive stars is sensitive to the 23 Na(a,p) 26 Mg cross section. Recent experimental data suggest the currently recommended cross sections are underestimated by a factor of 40. We present here differential cross sections f
or the 23 Na(a,p) 26 Mg reaction measured in the energy range E c.m. = 1.7 - 2.5 MeV. Concurrent measurements of Rutherford scattering provide absolute normalisations which are independent of variations in target properties. Angular distributions were measured for both p 0 and p 1 permitting the determination of total cross sections. The results show no significant deviation from the statistical model calculations upon which the recommended rates are based. We therefore retain the previous recommendation without the increase in cross section and resulting stellar reaction rates of a factor of 40, impacting on the 26 Al yield from massive stars by more than a factor of three.
Borromean nuclear cluster structures are expected at the corresponding driplines. We locate the regions in the nuclear chart with the most promising constituents, it being protons and alpha-particles and investigate in details the properties of the p
ossible borromean two-alpha systems in medium heavy nuclei. We find in all cases that the alpha-particles are located at the surface of the core-nucleus as dictated by Coulomb and centrifugal barriers. The two lowest three-body bound states resemble a slightly contracted $^{8}text{Be}$ nucleus outside the core. The next two excited states have more complex structures but with strong components of linear configurations with the core in the middle. Alpha-removal cross sections would be enhanced with specific signatures for these two different types of structures. The even-even borromean two-alpha nucleus, $^{142}$Ba, is specifically investigated and predicted to have $^{134}text{Te}-alpha-alpha$ structure in its ground state and low-lying spectrum.
