C. R. Hoffman

Direct Measurement of the

In our Letter [Phys. Rev. Lett. 112, 152701 (2014)] we reported the direct measurement of the 23Naðα; pÞ26Mg reaction cross section at energies relevant for the production of Galactic Al. Our results, which relied on the extracted absolute cross sections given in Table I, have been found to be in error, overestimating the reported cross sections by a factor of 100. In the experiment, protons from the reaction were measured in an annular silicon strip detector placed downstream from a cryogenic He gas target. The cross sections were normalized to the yield of scattered Na ions from a separate Au foil in an upstream monitor detector. The data acquisition system was triggered by a logic “OR” of the proton detector and the “downscaled” monitor detector. The monitor detector rate was downscaled in order to reduce dead time in the data acquisition system. The down-scale factor was n 1⁄4 100, while in the analysis, the factor was mistakenly taken as n 1⁄4 1. Therefore, the cross section numbers given in Table I should be divided by a factor of 100. The stellar rate reported in our Letter should also be down scaled by the same factor of 100, which makes it in agreement, within the experimental uncertainties, with the recommended rate. This problem came to light due to results from recent experiments where the same reaction was studied in regular and inverse kinematics [1,2]. Those studies obtained similar results and were in disagreement with our measurement. A subsequent experiment by our group was carried out with a different technique to verify the results. In this experiment, an active target and detector system measures both the heavy Mg recoils as well as the incoming Na beam, thus avoiding normalization errors [3]. The new results [3] are in agreement with the reported results [1,2] and also with the values in our Letter, within their experimental uncertainties, if the down-scale factor is correctly included.

^{23}

In reviewing the data that has accumulated in light nuclei we find that the binding energy plays a critical role in describing the variation in energy of

Na(

s

\alpha

states relative to other states. The behavior of states with zero angular momentum within a few MeV of threshold is qualitatively different from that of neutron states with any other

,p)

\ell

^{26}

value or of any proton state. This observation is explored for simple Woods-Saxon potentials and is remarkably successful in describing a wealth of experimental data for nuclei with neutron numbers between 5 and 10. The lingering of neutron

Mg Reaction Cross Section at Energies Relevant for the Production of Galactic

s

^{26}

states just below threshold is associated with the increases in radii of the neutron density distributions, the neutron halos, and leads to speculations about possible halos in heavier nuclei.

Al

The existence of ^{26}Al (t_{1/2}=7.17×10^{5}  yr) in the interstellar medium provides a direct confirmation of ongoing nucleosynthesis in the Galaxy. The presence of a low-lying 0^{+} isomer (^{26}Al^{m}), however, severely complicates the astrophysical calculations. We present for the first time a study of the ^{26}Al^{m}(d,p)^{27}Al reaction using an isomeric ^{26}Al beam. The selectivity of this reaction allowed the study of ℓ=0 transfers to T=1/2, and T=3/2 states in ^{27}Al. Mirror symmetry arguments were then used to constrain the ^{26}Al^{m}(p,γ)^{27}Si reaction rate and provide an experimentally determined upper limit of the rate for the destruction of isomeric ^{26}Al via radiative proton capture reactions, which is expected to dominate the destruction path of ^{26}Al^{m} in asymptotic giant branch stars, classical novae, and core collapse supernovae.

Neutronsstates in loosely bound nuclei

In our Letter [Phys. Rev. Lett. 112, 152701 (2014)] we reported the direct measurement of the 23Naðα; pÞ26Mg reaction cross section at energies relevant for the production of Galactic Al. Our results, which relied on the extracted absolute cross sections given in Table I, have been found to be in error, overestimating the reported cross sections by a factor of 100. In the experiment, protons from the reaction were measured in an annular silicon strip detector placed downstream from a cryogenic He gas target. The cross sections were normalized to the yield of scattered Na ions from a separate Au foil in an upstream monitor detector. The data acquisition system was triggered by a logic “OR” of the proton detector and the “downscaled” monitor detector. The monitor detector rate was downscaled in order to reduce dead time in the data acquisition system. The down-scale factor was n 1⁄4 100, while in the analysis, the factor was mistakenly taken as n 1⁄4 1. Therefore, the cross section numbers given in Table I should be divided by a factor of 100. The stellar rate reported in our Letter should also be down scaled by the same factor of 100, which makes it in agreement, within the experimental uncertainties, with the recommended rate. This problem came to light due to results from recent experiments where the same reaction was studied in regular and inverse kinematics [1,2]. Those studies obtained similar results and were in disagreement with our measurement. A subsequent experiment by our group was carried out with a different technique to verify the results. In this experiment, an active target and detector system measures both the heavy Mg recoils as well as the incoming Na beam, thus avoiding normalization errors [3]. The new results [3] are in agreement with the reported results [1,2] and also with the values in our Letter, within their experimental uncertainties, if the down-scale factor is correctly included.