Structure of 23Al from one-proton breakup reaction and astrophysical implications

The ground state of the proton-rich nucleus 23Al has been studied by one-proton removal on a carbon target at about 50 MeV/nucleon using the EXOGAM + SPEG experimental setup at GANIL. Longitudinal momentum distributions of the 22Mg breakup fragments, inclusive and in coincidence with gamma rays de-exciting the residues, were measured. The ground-state structure of 23Al is found to be a configuration mixing of a d-orbital valence proton coupled to four core states - 0$^{+}_{gs}$, 2$^{+}_{1}$, 4$^{+}_{1}$, 4$^{+}_{2}$. We confirm the ground state spin and parity of 23Al as $J^{pi} = 5/2^{+}$. The measured exclusive momentum distributions are compared with extended Glauber model calculations to extract spectroscopic factors and asymptotic normalization coefficients (ANCs). The spectroscopic factors are presented in comparison with those obtained from large-scale shell model calculations. We determined the asymptotic normalization coefficient of the nuclear system $^{23}$Al$_{gs}$ $rightarrow$ $^{22}$Mg(0$^{+}$) + p to be $C^{2}_{d_{5/2}}$($^{23}Al_{gs}$) = (3.90 $pm$ 0.44) $times$ 10$^{3}$ fm$^{-1}$, and used it to infer the stellar reaction rate of the direct radiative proton capture $^{22}$Mg(p,$gamma$)$^{23}$Al. Astrophysical implications related to $^{22}$Na nucleosynthesis in ONe novae and the use of one-nucleon breakup at intermediate energies as an indirect method in nuclear astrophysics are discussed.

Beta-delayed proton decay of proton-rich nuclei 23Al and 31Cl and explosive H-burning in classical novae

We have developed a technique to measure beta-delayed proton decay of proton-rich nuclei produced and separated with the MARS recoil spectrometer of Texas A&M University. The short-lived radioactive species are produced in-flight, separated, then slowed down (from about 40 MeV/u) and implanted in the middle of very thin Si detectors. The beam is pulsed and beta-p decay of the pure sources collected in beam is measured between beam pulses. Implantation avoids the problems with detector windows and allows us to measure protons with energies as low as 200 keV from nuclei with lifetimes of 100 ms or less. Using this technique, we have studied the isotopes 23Al and 31Cl, both important for understanding explosive H-burning in novae. They were produced in the reactions 24Mg(p,2n)23Al and 32S(p,2n)31Cl, respectively, in inverse kinematics, from stable beams at 48 and 40 MeV/u, respectively. We give details about the technique, its performances and the results for 23Al and 31Cl beta-p decay. The technique has shown a remarkable selectivity to beta-delayed charged-particle emission and would work even at radioactive beam rates of a few pps. The states populated are resonances for the radiative proton capture reactions 22Na(p,g)23Mg and 30P(p,g)31S, respectively.