Resonant elastic scattering of a radioactive Na20 beam incident upon protons in a polyethylene target has been used to probe the level structure of Mg21 above the proton decay threshold. Three states have been observed, and their properties deduced through analysis based on the R-matrix formalism. The results improve and extend previous studies of this nucleus. An estimate of the Na20(p,γ)Mg21 reaction rate, including these new data, suggests this reaction will not play a significant role in explosive hydrogen burning in astrophysical sites such as novae and x-ray bursts. © 2006 The American Physical Society.
- R-MATRIX THEORY