New pathway to bypass the 15O waiting point

We propose the sequential reaction process $^{15}$O($p$,$\gamma)(\beta^{+}$)$^{16}$O as a new pathway to bypass of the $^{15}$O waiting point. This exotic reaction is found to have a surprisingly high cross section, approximately 10$^{10}$ times higher than the $^{15}$O($p$,$\beta^{+}$)$^{16}$O. These cross sections were calculated after precise measurements of energies and widths of the proton-unbound $^{16}$F low lying states, obtained using the H($^{15}$O,p)$^{15}$O reaction. The large $(p,\gamma)(\beta^{+})$ cross section can be understood to arise from the more efficient feeding of the low energy wing of the ground state resonance by the gamma decay. The implications of the new reaction in novae explosions and X-ray bursts are discussed.Comment: submitte

Probing Nuclear forces beyond the drip-line using the mirror nuclei 16^{16}N and 16^{16}F

Radioactive beams of $^{14}$O and $^{15}$O were used to populate the resonant states 1/2$^+$, 5/2$^+$ and $0^-,1^-,2^-$ in the unbound $^{15}$F and $^{16}$F nuclei respectively by means of proton elastic scattering reactions in inverse kinematics. Based on their large proton spectroscopic factor values, the resonant states in $^{16}$F can be viewed as a core of $^{14}$O plus a proton in the 2s$_{1/2}$ or 1d$_{5/2}$ shell and a neutron in 1p$_{1/2}$. Experimental energies were used to derive the strength of the 2s$_{1/2}$-1p$_{1/2}$ and 1d$_{5/2}$-1p$_{1/2}$ proton-neutron interactions. It is found that the former changes by 40% compared with the mirror nucleus $^{16}$N, and the second by 10%. This apparent symmetry breaking of the nuclear force between mirror nuclei finds explanation in the role of the large coupling to the continuum for the states built on an $\ell=0$ proton configuration.Comment: 6 pages, 3 figures, 2 tables, accepted for publication as a regular article in Physical Review

Spectroscopy of 18^{18}Na: Bridging the two-proton radioactivity of 19^{19}Mg

The unbound nucleus $^{18}$Na, the intermediate nucleus in the two-proton radioactivity of $^{19}$Mg, was studied by the measurement of the resonant elastic scattering reaction $^{17}$Ne(p,$^{17}$Ne)p performed at 4 A.MeV. Spectroscopic properties of the low-lying states were obtained in a R-matrix analysis of the excitation function. Using these new results, we show that the lifetime of the $^{19}$Mg radioactivity can be understood assuming a sequential emission of two protons via low energy tails of $^{18}$Na resonances

Spectroscopy of the unbound nucleus 18Na

Expérience GANIL, SPIRALInternational audienceThe unbound nucleus 18Na, the intermediate nucleus in the two-proton radioactivity of 19Mg, is studied through the resonant elastic scattering 17Ne(p,17Ne)p. The spectroscopic information obtained in this experiment is discussed and put in perspective with previous measurements and the structure of the mirror nucleus 18N

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.

An above-barrier narrow resonance in F-15

Intense and purified radioactive beam of post-accelerated O-14 was used to study the low-lying states in the unbound F-15 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 C-12 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. (C) 2016 The Authors. Published by Elsevier B.V

Study of 15^{15}F energy levels

Expérience GANIL E521

Premiers états du 15^{15}F étudiés par diffusion élastique résonante

This thesis describes the study of a light neutron deficient nucleus located beyond the proton drip-line : 15F. This unbound nucleus was studied using the resonant elastic scattering reaction : 14O(p,14O)p, performed in inverse kinematics. The radioactive ions beam produced by the GANIL SPIRAL facility, impinged a thick polypropylene target. Excitation function was measured up to 5.6 MeV in the center of mass and three resonances were observed. The ground and first excited state of 15F are observed as broad resonances corresponding to very short living states. The third resonance is due to a state with a spin and parity 1/2− which is observed for the first time. It is located 4.78 MeV above the proton emission threshold. Surprisingly, this resonance is very narrow, corresponding to a long living state. This state lies 160 keV above the two-proton threshold, which makes it a candidate for 2-proton emission. Several decay channels were discussed for this state, including a proton-gamma decay via the tail of first excited state resonance in 14O. Results are discussed in terms of nuclear structure and the existence of two-proton of proton-gamma decay.Cette thèse s'inscrit dans le cadre de l'étude des noyaux déficients en neutrons situés au delà de la drip-line proton. Afin d'étudier le noyau de 15F, une expérience de diffusion élastique résonante d'un faisceau d'ions radioactifs d'14O sur une cible épaisse composée de protons,c'est à dire la réaction 14O(p,14O)p, a été réalisée au GANIL avec un faisceau post-accéléré SPIRAL. La fonction d'excitation du 15F a été mesurée jusqu'à 5.6MeV d'énergie dans le centre de masse et a révélé la présence de trois résonances, dont l'une correspond à un état étroit de parité négative observé pour la première fois. Cet état a été analysé comme pouvant décroître sur deux voies de décroissance, l'une correspondant à l'émission d'un seul proton et l'autre interprétée comme une émission (pγ) procédant via la queue basse énergie d'un état excité de l'14O. L'interprétation des résultats obtenus en terme de structure du noyau et l'existence d'une décroissance deux proton ou (pγ) est discutée

Measurements of nuclear γ\gamma-ray line emission in interactions of protons and α\alpha particles with N, O, Ne and Si.

42 pages, 12 figures, 7 tables, submitted to Phys. Rev. CInternational audience$\gamma$-ray production cross sections have been measured in proton irradiations of N, Ne and Si and $\alpha$-particle irradiations of N and Ne. In the same experiment we extracted also line shapes for strong $\gamma$-ray lines of $^{16}$O produced in proton and $\alpha$-particle irradiations of O. For the measurements gas targets were used for N, O and Ne and a thick foil was used for Si. All targets were of natural isotopic composition. Beams in the energy range up to 26 MeV for protons and 39 MeV for $\alpha$-particles have been delivered by the IPN-Orsay tandem accelerator. The $\gamma$ rays have been detected with four HP-Ge detectors in the angular range 30$^{\circ}$ to 135$^{\circ}$. We extracted 36 cross section excitation functions for proton reactions and 14 for $\alpha$-particle reactions. For the majority of the excitation functions no other data exist to our knowledge. Where comparison with existing data was possible usually a very good agreement was found. It is shown that these data are very interesting for constraining nuclear reaction models. In particular the agreement of cross section calculations in the nuclear reaction code TALYS with the measured data could be improved by adjusting the coupling schemes of collective levels in the target nuclei $^{14}$N, $^{20,22}$Ne and $^{28}$Si. The importance of these results for the modeling of nuclear $\gamma$-ray line emission in astrophysical sites is discussed