Astrophysical S factor for the radiative capture 12N(p,gamma)13O determined from the 14N(12N,13O)13C proton transfer reaction

The cross section of the radiative proton capture reaction on the drip line nucleus 12N was investigated using the Asymptotic Normalization Coefficient (ANC) method. We have used the 14N(12N,13O)13C proton transfer reaction at 12 MeV/nucleon to extract the ANC for 13O -> 12N + p and calculate from it the direct component of the astrophysical S factor of the 12N(p,gamma)13O reaction. The optical potentials used and the DWBA analysis of the proton transfer reaction are discussed. For the entrance channel, the optical potential was inferred from an elastic scattering measurement carried out at the same time with the transfer measurement. From the transfer, we determined the square of the ANC, C^2(13Og.s.) = 2.53 +/- 0.30 fm-1, and hence a value of 0.33(4) keVb was obtained for the direct astrophysical S factor at zero energy. Constructive interference at low energies between the direct and resonant captures leads to an enhancement of Stotal(0) = 0.42(5) keVb. The 12N(p,gamma)13O reaction was investigated in relation to the evolution of hydrogen-rich massive Population III stars, for the role that it may play in the hot pp-chain nuclear burning processes, possibly occurring in such objects.Comment: 15 pages, 10 figures, 3 tables submitted to Phys. Rev.

Three-body decay of 6^{6}Be

Three-body correlations for the ground-state decay of the lightest two-proton emitter $^{6}$Be are studied both theoretically and experimentally. Theoretical studies are performed in a three-body hyperspherical-harmonics cluster model. In the experimental studies, the ground state of $^{6}$Be was formed following the $\alpha$ decay of a $^{10}$C beam inelastically excited through interactions with Be and C targets. Excellent agreement between theory and experiment is obtained demonstrating the existence of complicated correlation patterns which can elucidate the structure of $^{6}$Be and, possibly, of the A=6 isobar.Comment: 17 pages, 21 figures, 5 table

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.Comment: Submitted on Oct. 6, 2008 for the Proceedings of the 10th Symposium on Nuclei in the Cosmos Mackinac Island, Michigan, USA 27 July - 1 August, 2008 Acceptance pendin

Single and double proton emissions from the O-14+He-4 interaction

Journals published by the American Physical Society can be found at http://publish.aps.org/We observed single and double proton emissions in the O-14+He-4 interaction by the thick target inverse kinematic (TTIK) method at initial energy for O-14 at 32.7 MeV. We found that the protons mainly originate from the resonance excitation of states in Ne-18. The observed states in Ne-18 decay by protons mainly to proton unstable states in F-17. It was found that the decay of a state in Ne-18 at E-ex=8.45 MeV demonstrates the features of a decay by a correlated proton pair. The observed properties of the O-14+He-4 interaction make a previous interpretation for the rate of O-14(He-4, p)F-17 at astrophysical energies suspect. We show how the TTIK method should be modified to obtain the data of astrophysical interest

Experimental study of beta-delayed proton decay of (23)Al for nucleosynthesis in novae

Journals published by the American Physical Society can be found at http://publish.aps.org/The beta-delayed gamma and proton decay of (23)Al has been studied with an alternative detector setup at the focal plane of the momentum achromat recoil separator MARS at Texas AandM University. We could detect protons down to an energy of 200 keV and determine the corresponding branching ratios. Contrary to results of previous beta-decay studies, no strong proton intensity from the decay of the isobaric analog state (IAS) of the (23)Al ground state at E(x) = 7803 keV in (23)Mg was observed. Instead we assign the observed low-energy group E(p,c.m.) = 206 keV to the decay from a state that is 16 keV below the IAS. We measured both proton and gamma branches from the decay of this state at E(x) = 7787 keV in (23)Mg, which is a very rare case in the literature. Combining our data with its measured lifetime, we determine its resonance strength to be omega gamma = 1.4(-0.4)(+0.5) meV. The value is in agreement with older direct measurements, but disagrees with a recent direct measurement. This state is the most important resonance for the radiative proton capture (22)Na(p, gamma)(23)Mg in some astrophysical environments, such as novae

Uranyl oxo activation and functionalization by metal cation coordination

International audienceThe oxo groups in the uranyl ion [UO$_2$]$^{2+}$ , one of many oxo cations formed by metals from across the periodic table—are particularly inert, which explains the dominance of this ion in the laboratory and its persistence as an environmental contaminant. In contrast, transition metal oxo (M=O) compounds can be highly reactive and carry out difficult reactions such as the oxygenation of hydrocarbons. Here we show how the sequential addition of a lithium metal base to the uranyl ion constrained in a ‘Pacman’ environment results in lithium coordination to the U=O bonds and single-electron reduction. This reaction depends on the nature and stoichiometry of the lithium reagent and suggests that competing reduction and C–H bond activation reactions are occurring

An above-barrier narrow resonance in ¹⁵F

Intense and purified radioactive beam of post-accelerated $^{14}$O was used to study the low-lying states in the unbound $^{15}$F nucleus. Exploiting resonant elastic scattering in inverse kinematics with a thick target, the second excited state, a resonance at E$\_R$=4.757(6)(10)~MeV with a width of $\Gamma$=36(5)(14)~keV was measured for the first time with high precision. The structure of this narrow above-barrier state in a nucleus located two neutrons beyond the proton drip line was investigated using the Gamow Shell Model in the coupled channel representation with a $^{12}$C core and three valence protons. It is found that it is an almost pure wave function of two quasi-bound protons in the $2s\_{1/2}$ shell.Comment: 8 pages, 2 figures, 1 table, Submitted to Phys. Lett.

First observation of alpha-cluster states in the (14)O+(4)He interaction

Journals published by the American Physical Society can be found at http://publish.aps.org/We measured (14)O+(4)He excitation functions for elastic scattering which demonstrate, for the first time, a well developed alpha-cluster structure in the proton rich nucleus, (18)Ne. We present the excitation energies and estimates of the spins for the dominant resonances using an R-matrix approach. A resonance at 9.2 MeV excitation energy in (18)Ne is particularly interesting. The spin-parity of the state is found to be 3(-) and the alpha particle reduced width for the state appears to be comparable to the single particle limit. We have found indications for unusually large size of the observed alpha-cluster configuration