Measurement of Mg23(p,γ)Al24 resonance energies

D. W. Visser, ORNL Physics Division
C. Wrede, Yale University
J. A. Caggiano, Yale University
J. A. Clark, Yale University
C. Deibel, Yale University
R. Lewis, Yale University
A. Parikh, Yale University
P. D. Parker, Yale University


The existence of two systematically inconsistent sets of measurements of the Al24 excitation energies, which are used to determine Mg23+p resonance energies, results in a variation of a factor 5 in the thermonuclear Mg23(p,γ)Al24 reaction rate at T=0.25 GK. The astrophysically important energies have been determined to an uncertainty of 6 keV by measuring triton spectra from the Mg24(He3,t)Al24 reaction at E(He3)=30 MeV, and good general agreement is found with one previous set. The present measurement of Ex=2346(6) keV for what is thought to be the most important resonance is, however, in disagreement with both prior measurements of 2328(10) and 2369(4) keV, where the latter value belongs to the outlying set. The presently determined resonance energies reduce the related uncertainty in the Mg23(p,γ)Al24 reaction rate by a factor of 3, which will constrain the determination of nuclear flow out of the NeNa cycle, and production of A≥20 nuclides, in explosive hydrogen burning over a temperature range 0.2