Weakly bound systems, continuum effects, and reactions

Structure of weakly bound/unbound nuclei close to particle drip lines is different from that around the valley of beta stability. A comprehensive description of these systems goes beyond standard Shell Model and demands an open quantum system description of the nuclear many-body system. We approach this problem using the Gamow Shell Model which provides a fully microscopic description of bound and unbound nuclear states, nuclear decays, and reactions. We present in this paper the first application of the GSM for a description of the elastic and inelastic scattering of protons on 6He.Comment: Proc. Int. Conf. "Horizons of Innovative Theories, Experiments and Supercomputing in Nuclear Physics", June 4-7, 2012, New Orleans, Luisiana, USA; 10 pages, 4 figure

Nuclear rotation in the continuum

${\textbf{Background:}}$ Atomic nuclei often exhibit collective rotational-like behavior in highly excited states, well above the particle emission threshold. What determines the existence of collective motion in the continuum region, is not fully understood. ${\textbf{Purpose:}}$ In this work, by studying the collective rotation of the positive-parity deformed configurations of the one-neutron halo nucleus $^{11}$Be, we assess different mechanisms that stabilize collective behavior beyond the limits of particle stability. ${\textbf{Method:}}$ To solve a particle-plus-core problem, we employ a non-adiabatic coupled-channel formalism and the Berggren single-particle ensemble, which explicitly contains bound states, narrow resonances, and the scattering continuum. We study the valence-neutron density in the intrinsic rotor frame to assess the validity of the adiabatic approach as the excitation energy increases. ${\textbf{Results:}}$ We demonstrate that collective rotation of the ground band of $^{11}$Be is stabilized by (i) the fact that the $\ell=0$ one-neutron decay channel is closed, and (ii) the angular momentum alignment, which increases the parentage of high-$\ell$ components at high spins; both effects act in concert to decrease decay widths of ground-state band members. This is not the case for higher-lying states of $^{11}$Be, where the $\ell=0$ neutron-decay channel is open and often dominates. ${\textbf{Conclusion:}}$ We demonstrate that long-lived collective states can exist at high excitation energy in weakly bound neutron drip-line nuclei such as $^{11}$Be

Description of the proton and neutron radiative capture reactions in the Gamow shell model

We formulate the Gamow shell model (GSM) in coupled-channel (CC) representation for the description of proton/neutron radiative capture reactions and present the first application of this new formalism for the calculation of cross-sections in mirror reactions 7Be(p,gamma)8B and 7Li(n,gamma)8Li. The GSM-CC formalism is applied to a translationally-invariant Hamiltonian with an effective finite-range two-body interaction. Reactions channels are built by GSM wave functions for the ground state 3/2- and the first excited state 1/2- of 7Be/7Li and the proton/neutron wave function expanded in different partial waves

Gamow shell model description of radiative capture reactions 6^6Li(p,γ)(p,\gamma)7^7Be and 6^6Li(n,γ)(n,\gamma)7^7Li

According to standard stellar evolution, lithium abundance is believed to be a useful indicator of the stellar age. However, many evolved stars like red giants show huge fluctuations around expected theoretical abundances that are not yet fully understood. The better knowledge of nuclear reactions that contribute to the creation and destruction of lithium can help to solve this puzzle. In this work we apply the Gamow shell model (GSM) formulated in the coupled-channel representation (GSM-CC) to investigate the mirror radiative capture reactions $^6$Li$(p,\gamma)$$^7$Be and $^6$Li$(n,\gamma)$$^7$Li. The cross-sections are calculated using a translationally invariant Hamiltonian with the finite-range interaction which is adjusted to reproduce spectra, binding energies and one-nucleon separation energies in $^{6-7}$Li, $^7$Be. All relevant $E1$, $M1$, and $E2$ transitions from the initial continuum states to the final bound states $J={3/2}_1^-$ and $J={1/2}^-$ of $^7$Li and $^7$Be are included. We demonstrate that the $s$-wave radiative capture of proton (neutron) to the first excited state $J^{\pi}=1/2_1^+$ of $^7$Be ($^7$Li) is crucial and increases the total astrophysical $S$-factor by about 40 \%.Comment: arXiv admin note: text overlap with arXiv:1502.0163

Bound and resonance states of the dipolar anion of hydrogen cyanide: competition between threshold effects and rotation in an open quantum system

Bound and resonance states of the dipole-bound anion of hydrogen cyanide HCN$^-$ are studied using a non-adiabatic pseudopotential method and the Berggren expansion technique involving bound states, decaying resonant states, and non-resonant scattering continuum. We devise an algorithm to identify the resonant states in the complex energy plane. To characterize spatial distributions of electronic wave functions, we introduce the body-fixed density and use it to assign families of resonant states into collective rotational bands. We find that the non-adiabatic coupling of electronic motion to molecular rotation results in a transition from the strong-coupling to weak-coupling regime. In the strong coupling limit, the electron moving in a subthreshold, spatially extended halo state follows the rotational motion of the molecule. Above the ionization threshold, electron's motion in a resonance state becomes largely decoupled from molecular rotation. Widths of resonance-band members depend primarily on the electron orbital angular momentum.Comment: 11 pages, 13 figure

Gamow Shell Model description of Li isotopes and their mirror partners

Background: Weakly bound and unbound nuclei close to particle drip lines are laboratories of new nuclear structure physics at the extremes of neutron/proton excess. The comprehensive description of these systems requires an open quantum system framework that is capable of treating resonant and nonresonant many-body states on equal footing. Purpose: In this work, we construct the minimal complex-energy configuration interaction approach to describe binding energies and spectra of selected 5 $\leq$ A $\leq$ 11 nuclei. Method: We employ the complex-energy Gamow shell model (GSM) assuming a rigid $^4$He core. The effective Hamiltonian, consisting of a core-nucleon Woods-Saxon potential and a simplified version of the Furutani-Horiuchi-Tamagaki interaction with the mass-dependent scaling, is optimized in the sp space. To diagonalize the Hamiltonian matrix, we employ the Davidson method and the Density Matrix Renormalization Group technique. Results: Our optimized GSM Hamiltonian offers a good reproduction of binding energies and spectra with the root-mean-square (rms) deviation from experiment of 160 keV. Since the model performs well when used to predict known excitations that have not been included in the fit, it can serve as a reliable tool to describe poorly known states. A case in point is our prediction for the pair of unbound mirror nuclei $^{10}$Li-$^{10}$N in which a huge Thomas-Ehrman shift dramatically alters the pattern of low-energy excitations. Conclusion: The new model will enable comprehensive studies of structure and reactions aspects of light drip-line nuclei.Comment: 11 pages, 3 figure

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.

Cultiver la tolérance à l'école à travers les albums de jeunesse

Professorat des écolesChaque jour, l'intolérance s'exprime à travers le monde en événements plus ou moins tragiques. En tant qu'enseignant, on est souvent témoin des difficultés qu'ont les uns et les autres, petits ou grands, à vivre ensemble en se respectant mutuellement. Alors peut-on enseigner la tolérance à nos élèves ? Peut-on cultiver cette notion à l'école pour éventuellement la faire germer au sein des générations qui bâtiront le monde de demain ? Une piste de travail est proposée dans ce mémoire à travers un projet d'écriture d'album de jeunesse mené avec des élèves de cycle 3. Ces derniers ont réalisé eux-mêmes les textes et les illustrations d'un album évoquant la tolérance et le respect des différences