Level structure of Mg21: Nuclear and astrophysical implications
Resonant elastic scattering of a radioactive $^{20}\mathrm{Na}$ beam incident upon protons in a polyethylene target has been used to probe the level structure of $^{21}\mathrm{Mg}$ 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 $^{20}\mathrm{Na}$(p,\ensuremath{\gamma})$^{21}\mathrm{Mg}$ 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.
The Boundary Condition Parameter in R-Matrix Theory
In the general R-matrix theory of nuclear reactions, all measurable quantities such as the cross sections scc' should be independent of the choice of the boundary condition parameters Bc although the values of the level parameters E? and ??c depend on the Bc. For applications involving only a finite number of levels ?, it is not obvious that this is still the case as completeness arguments can no longer be used. It is shown here that scc' can be made independent of the choice Bc of for any finite number of levels and any number of channels, and the resulting formulae giving the dependence of E? and ??c on Bc are derived. An application is made to the pair of 5/2- levels of 7Li near 7 MeV excitation.
The DSA lifetime of the 2425 keV state in 21Na
The lifetime of the sub-threshold Ep=-7 keV resonance state at Ex=2425 keV in 21Na has been determined as 3.9+or-1.1 fs. The DSA method and direct capture in the 20Ne(p, gamma )21Na reaction have been employed. The result obtained is discussed in terms of the single-particle character and astrophysical aspects are considered.