Search

Shell structure effects on $\ensuremath{\alpha}$-cluster formation and decay are studied by using the quartetting wave function approach (QWFA). Both the intrinsic and center-of-mass (c.o.m.) motions of an $\ensuremath{\alpha}$ cluster inside a core nucleus are investigated with different contributing shell model wave functions. The overlap between intrinsic wave functions of four nucleons in the $\ensuremath{\alpha}$-like quartet state and in a free $\ensuremath{\alpha}$ particle is analyzed in detail. The change of the effective potential describing the c.o.m. motion of the quartet is explicitly shown for the major shell closures $Z=82$ and $N=126$. It is found that both the $\ensuremath{\alpha}$-cluster formation probability and the half-life are sensitive to the quartet shell model states. By extending the QWFA calculations from $^{212}\mathrm{Po}$ to $\ensuremath{\alpha}$ emitters with one or two extra nucleons, we show that the bound state and scattering wave functions of the $\ensuremath{\alpha}$ cluster are changed accordingly. The calculated $\ensuremath{\alpha}$-decay half-lives agree nicely with the experimental data.

The elastic transverse electron scattering form factors have been studied for the 11Li nucleus using the Two- Frequency Shell Model (TFSM) approach. The single-particle wave functions of harmonic-oscillator (HO) potential are used with two different oscillator parameters bcore and bhalo. According to this model, the core nucleons of 9Li nucleus are assumed to move in the model space of spsdpf. The outer halo (2-neutron) in 11Li is assumed to move in the pure 1p1/2, 1d5/2, 2s1/2 orbit. The shell model calculations are carried out for core nucleons using the spsdpf-interaction. The elastic magnetic electron scattering of the stable 7Li and exotic 11Li nuclei are also investigated through Plane Wave Born Approximation (PWBA). It is found that the difference between the total form factors of unstable isotope (11Li halo) and stable isotope 7Li is in magnitude. The measured value of the magnetic moment is also reproduced.

The Borromean halo nucleus 6He has been studied by a kinematically complete measurement of Coulomb and nuclear breakup into α + 2n on Pb and C targets at 70 MeV/nucleon. Fully quantum-mechanical four-body breakup calculations reproduce the energy and angular differential cross sections below E rel ∼ 1 MeV for both targets. The model used here reproduces the 6He ground-state properties as well as α-n and n-n scattering data and predicts an average opening angle 〈 θ n n 〉 of 68∘ between the two halo neutrons. However, the model underestimates the breakup cross sections for higher E rel , indicating a possible contribution from the inelastic breakup. Alternatively, we examine the empirically modified calculations that reproduce the energy-differential cross sections for a wide range of scattering angles for both targets. The extracted B(E1) peaks at E rel ∼ 1.4 MeV and amounts to 1.6(2) e2 fm2 for E rel ≤ 20 MeV, resulting 〈 θ n n 〉 = 56 − 10 + 9 degrees. In either interpretation, the current results show evidence of the dineutron spatial correlation in 6He.

An experimental investigation of the reaction of core pickup from 6He and 11Li two-neutronhalo nuclei is proposed. In such experiments, neutron–neutron correlations in a halo nucleus will be assessed on the basis of the energy of a neutron–neutron quasibound state. A detailed kinematical simulation of the reaction 6He + 2H → 6Li + (nn) →6 Li + n + n is performed. It is shown that the energy of the quasibound state in question can determined from the shape of the energy spectrum of neutrons originating from the breakup of this state. In the proposed exclusive experiment, a beam of 6He (11Li) nuclei with an energy of about 5 to 10 MeV per nucleon interacts with a deuterated-polyethylene target. This will permit detecting charged particles (6Li and 11Be) and a neutron. On the basis of determining the energy of the neutron–neutron quasibound state, it will become possible to estimate the effective attraction between the valence neutrons in the field of the third particle (core).

Quartetting ( $$\alpha $$ -like clustering) occurs in low-density matter ( $${\le }0.03$$ fm $$^{-3}$$ ) which exists, e.g., at the surface of nuclei. It is of interest for the $$\alpha $$ preformation to calculate the $$\alpha $$ decay of heavy nuclei such as $$^{212}$$ Po, but also in light nuclei (e.g., $$^{20}$$ Ne) which shows strong signatures of quartetting. We analyze the intrinsic structure of the $$\alpha $$ -like cluster and the center-of-mass motion of the quartet, in particular the role of Pauli blocking. The Thomas–Fermi model for the (daughter) core nucleus is improved introducing quasiparticle nucleon states. Calculations performed for harmonic oscillator basis states show that the effective potential for the quartet center-of-mass motion remains nearly constant within the core nucleus. The relation to the (Tohsaki–Horiuchi–Schuck–Ropke) THSR approach is discussed.

The low-lying unbound level structure of the halo nucleus 19C has been investigated using single-neutron knockout from 20C on a carbon target at 280 MeV/nucleon. The invariant mass spectrum, derived from the momenta of the forward going beam velocity 18C fragment and neutrons, was found to be dominated by a very narrow near threshold ( E rel = 0.036 ( 1 ) MeV) peak. Two less strongly populated resonance-like features were also observed at E rel = 0.84 ( 4 ) and 2.31 ( 3 ) MeV, both of which exhibit characteristics consistent with neutron p-shell hole states. Comparisons of the energies, measured cross sections and parallel momentum distributions to the results of shell-model and eikonal reaction calculations lead to spin-parity assignments of 5 / 2 1 + and 1 / 2 1 − for the levels at E x = 0.62 ( 9 ) and 2.89 ( 10 ) MeV with S n = 0.58 ( 9 ) MeV. Spectroscopic factors were also deduced and found to be in reasonable accord with shell-model calculations. The valence neutron configuration of the 20C ground state is thus seen to include, in addition to the known 1 s 1 / 2 2 component, a significant 0 d 5 / 2 2 contribution. The level scheme of 19C, including significantly the 1 / 2 1 − cross-shell state, is well accounted for by the YSOX shell-model interaction developed from the monopole-based universal interaction.

Background: The neutron-rich $^{28,29}\mathrm{F}$ isotopes have been recently studied via knockout and interaction cross-section measurements. The two-neutron halo in $^{29}\mathrm{F}$ has been linked to the occupancy of $pf$ intruder configurations.Purpose: We investigate the bound spectrum and continuum states in $^{29}\mathrm{F}$, focusing on the electric dipole $(E1)$ response of low-lying excitations and the effect of dipole couplings on nuclear reactions.Method: $^{29}\mathrm{F}$ $(^{27}\mathrm{F}+n+n)$ wave functions are built within the hyperspherical harmonics expansion formalism, and total reaction cross sections are calculated using the Glauber theory. Continuum states and $B(E1)$ transition probabilities are described in a pseudostate approach using the analytical transformed harmonic oscillator basis. The corresponding structure form factors are used in continuum-discretized coupled-channels (CDCC) calculations to describe low-energy scattering.Results: Parity inversion in $^{28}\mathrm{F}$ leads to a $^{29}\mathrm{F}$ ground state characterized by 57.5% of ${({p}_{3/2})}^{2}$ intruder components, a strong dineutron configuration, and an increase of the matter radius with respect to the core radius of $\mathrm{\ensuremath{\Delta}}R=0.20$ fm. Glauber-model calculations for a carbon target at 240 MeV/nucleon provide a total reaction cross section of 1370 mb, in agreement with recent data. The model produces also a barely bound excited state corresponding to a quadrupole excitation. $B(E1)$ calculations into the continuum yield a total strength of 1.59 ${e}^{2}$ ${\mathrm{fm}}^{2}$ up to 6 MeV, and the $E1$ distribution exhibits a resonance at $\ensuremath{\approx}0.85$ MeV. Results using a standard shell-model order for $^{28}\mathrm{F}$ lead to a considerable reduction of the $B(E1)$ distribution. The four-body CDCC calculations for $^{29}\mathrm{F}+^{120}\mathrm{Sn}$ around the Coulomb barrier are dominated by dipole couplings, which totally cancel the Fresnel peak in the elastic-scattering cross section.Conclusions: Our three-body calculations for $^{29}\mathrm{F}$, using the most recent experimental information on $^{28}\mathrm{F}$, are consistent with a two-neutron halo. Our predictions show the low-lying enhancement of the $E1$ response expected for halo nuclei and the relevance of dipole couplings for low-energy reactions on heavy targets. These findings may guide future experimental campaigns.

Background: Aside from being a one-neutron halo nucleus, $^{15}\mathrm{C}$ is interesting because it is involved in reactions of relevance for several nucleosynthesis scenarios.Purpose: The aim of this work is to analyze various reactions involving $^{15}\mathrm{C}$, using a single structure model based on halo effective field theory (halo EFT) following the excellent results obtained in [P. Capel et al., Phys. Rev. C 98, 034610 (2018)].Method: To develop a halo-EFT model of $^{15}\mathrm{C}$ at next to leading order (NLO), we first extract the asymptotic normalization coefficient (ANC) of its ground state by analyzing $^{14}\mathrm{C}(d,p)^{15}\mathrm{C}$ transfer data at low energy using the method developed in [J. Yang and P. Capel, Phys. Rev. C 98, 054602 (2018)]. Using the halo-EFT description of $^{15}\mathrm{C}$ constrained with this ANC, we study the $^{15}\mathrm{C}$ Coulomb breakup at high (605 MeV/nucleon) and intermediate (68 MeV/nucleon) energies using eikonal-based models with a consistent treatment of nuclear and Coulomb interactions at all orders, and which take into account proper relativistic corrections. Finally, we study the $^{14}\mathrm{C}(n,\ensuremath{\gamma})^{15}\mathrm{C}$ radiative capture.Results: Our theoretical cross sections are in good agreement with experimental data for all reactions, thereby assessing the robustness of the halo-EFT model of this nucleus. Since a simple NLO description is enough to reproduce all data, the only nuclear-structure observables that matter are the $^{15}\mathrm{C}$ binding energy and its ANC, showing that all the reactions considered are purely peripheral. In particular, it confirms the value we have obtained for the ANC of the $^{15}\mathrm{C}$ ground state: ${\mathcal{C}}_{1/{2}^{+}}^{2}=1.59\ifmmode\pm\else\textpm\fi{}0.06\phantom{\rule{4pt}{0ex}}{\mathrm{fm}}^{\ensuremath{-}1}$. Our model of $^{15}\mathrm{C}$ provides also a new estimate of the radiative-capture cross section at astrophysical energy: ${\ensuremath{\sigma}}_{n,\ensuremath{\gamma}}(23.3\phantom{\rule{0.16em}{0ex}}\mathrm{keV})=4.66\ifmmode\pm\else\textpm\fi{}0.14\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{b}$.Conclusions: Including a halo-EFT description of $^{15}\mathrm{C}$ within precise models of reactions is confirmed to be an excellent way to relate the reaction cross sections and the structure of the nucleus. Its systematic expansion enables us to establish how the reaction process is affected by that structure and deduce which nuclear-structure observables are actually probed in the collision. From this, we can infer valuable information on both the structure of $^{15}\mathrm{C}$ and its synthesis through the $^{14}\mathrm{C}(n,\ensuremath{\gamma})^{15}\mathrm{C}$ radiative capture at astrophysical energies.

The ratio method has been developed to improve the study of one-neutron halo nuclei through reactions. By taking the ratio of angular distributions for two processes, viz. breakup and elastic scattering, this new observable is nearly independent of the reaction mechanism and hence much more sensitive to the projectile structure than the cross sections for each single process. We study the extension of the ratio method to proton-rich nuclei and also explore the optimum experimental conditions for measuring this new observable. We compare accurate dynamical calculations of reactions for proton-rich projectiles to the prediction of the ratio method. We use the dynamical eikonal approximation that provides good results for this kind of reactions at intermediate energy. Our tests for 8B, an archteypical one-proton halo nucleus, on Pb, Ni, and C targets at 44 MeV/nucleon show that, the ratio works less well than for neutron halos due to the non-negligible Coulomb interaction between the valence proton and the target. Nevertheless, the ratio method still provides pertinent information about nuclear structure on the proton-rich side of the valley of stability. Interestingly the method is not affected if energy ranges-or bins-are considered in the projectile continuum. This makes the ratio easier to measure experimentally by increasing the breakup cross section. We also extend our analysis to 17F, 25Al, and 27P, whose study is of interest to both nuclear astrophysics and nuclear structure. We show that, albeit less precise than for one-neutron halo nuclei, nuclear-structure information can be inferred from the ratio method applied to exotic proton-rich nuclei. In particular, when the valence proton is loosely bound in an $s$ or $p$ orbital, viz. for proton halo nuclei, detailed structure information can be obtained through this new reaction observable.

$\ensuremath{\alpha}$ clustering in nuclei is considered with the quartet model (QM) where four valence nucleons (the quartet) move on the top of the core (daughter) nucleus. In the QM approach, it is assumed that the intrinsic wave function of the quartet is changed from the pure cluster configuration to the shell-model configuration when it crosses some critical radius and enters into the core nucleus. The QM approach could give not only the level scheme, the electromagnetic transition, and the nuclear radius but also the $\ensuremath{\alpha}$-cluster formation probability. Numerical results are calculated for $^{20}\mathrm{Ne}$, $^{44}\mathrm{Ti}$, and $^{212}\mathrm{Po}$, where a quartet moves on top of a double magic nucleus. Good agreement with experimental data and previous theoretical studies is obtained. The QM approach is a useful complement to the present phenomenological and microscopic models and could help deepen our understanding of $\ensuremath{\alpha}$ clustering across the nuclide chart.

Previous studies of $(d,p)$ reactions in three-body (proton, neutron, nuclear core) systems revealed a nontrivial effect of the core excitation: the transfer cross section cannot be factorized into the spectroscopic factor and the single-particle cross section obtained neglecting the core excitation. This observable, up to a kinematic factor, is the angular distribution of the core nucleus in the $(p,d)$ reaction. The study of the core excitation effect for the most closely related observable in the $(p,pn)$ three-body breakup, i.e., the core angular distribution, is aimed in the present work. Breakup of the one-neutron halo nucleus in the collision with the proton is described using three-body Faddeev-type equations extended to include the excitation of the nuclear core. The integral equations for transition operators are solved in the momentum-space partial-wave representation. Breakup of 11Be nucleus as well as of model $A=11$ $p$-wave nuclei is studied at beam energies of 30, 60, and 200 MeV per nucleon. Angular and momentum distributions for the 10Be core in ground and excited states is calculated. In sharp contrast to $(p,d)$ reactions, the differential cross section in most cases factorizes quite well into the spectroscopic factor and the single-particle cross section. Due to different reaction mechanisms the core excitation effect in the breakup is very different from transfer reactions. A commonly accepted approach to evaluate the cross section, i.e., the rescaling of single-particle model results by the corresponding spectroscopic factor, appears to be reliable for breakup though it fails in general for transfer reactions., 6 pages, 5 figures, to be published in Phys. Rev. C

In this work, p-6,8He elastic scattering differential cross sections in the energy range 25 ∼ 73 MeV/nucleon have been studied by applying the Coulomb modified Glauber scattering formalism. Three different density distribution models for proton and neutron densities have been used in calculating the differential cross sections. With the Bhagwat, Gambhir and Patil (BGP) nuclear density model, the calculated rms matter radius for 6He is found to be 2.49 fm which is larger than the experimental value 2.33 ± 0.04 fm while, for 8He it comes out to be 2.47 fm which is close to the experimental value 2.45 ± 0.07 fm. In general, the comparative analyses of the elastic scattering cross sections with different density models indicate that the calculation with BGP model density is qualitatively more successful to reproduce the p-6,8He experimental data. We emphasize that within the analyses no adjustable parameters are employed to fit the available experimental data. By varying the parameters of the spin-dependent amplitude, a very close agreement has been obtained in a simultaneous χ 2-fitting to the polarization data for p-6He elastic scattering measured at 71 MeV/nucleon. The total reaction cross sections for p-6,8He at these energies have also been compared with the corresponding cross sections obtained reported in earlier studies.

Background: Information about the structure of halo nuclei are often inferred from one-neutron knockout reactions. Typically the parallel-momentum distribution of the remaining core is measured after a high-energy collision of the exotic projectile with a light target. Purpose:We study how the structure of halo nuclei affects knockout observables considering an eikonal model of reaction. Method: To evaluate the sensitivity of both the diffractive and stripping parallel-momentum distributions to the structure of halo nuclei, we consider several descriptions of the projectile within a halo effective-field theory. We consider the case of Be11, the archetypical one-neutron halo nucleus, impinging on C12 at 68 MeV/nucleon, which are usual experimental conditions for such measurements. The low-energy constants of the description of Be11 are fit to experimental data as well as to predictions of an ab initio nuclear-structure model. Results: The one-neutron knockout reaction is confirmed to be purely peripheral, the parallel-momentum distribution of the remaining core is sensitive only to the asymptotics of the ground-state wave function and not to its norm. The presence of an excited state in the projectile spectrum reduces the amplitude of the breakup cross section; the corresponding probability flux is transferred to the inelastic-scattering channel. Although the presence of a resonance in the core-neutron continuum significantly affects the energy distribution, it has no impact on the parallel-momentum distribution. Conclusions: The one-neutron knockout cross section can be used to infer information about the tail of the ground-state wave function, viz. its asymptotic normalization coefficient (ANC). The independence of the parallel-momentum distribution on the continuum description makes the extraction of the ANC from this observable very reliable., SCOPUS: ar.j, info:eu-repo/semantics/published

We analyze the breakup of the one-neutron halo nucleus 11Be measured at 520 MeV/nucleon at GSI on Pb and C targets within an eikonal description of the reaction including a proper treatment of special relativity. The Coulomb term of the projectile-target interaction is corrected at first order, while its nuclear part is described at the optical limit approximation. Good agreement with the data is obtained using a description of 11Be, which fits the breakup data of RIKEN. This solves the apparent discrepancy between the dB(E1)/dE estimations from GSI and RIKEN for this nucleus., SCOPUS: ar.j, info:eu-repo/semantics/published

The neutron-unbound isotope Be-13 has been studied in several experiments using different reactions, different projectile energies, and different experimental setups. There is, however, no real consensus in the interpretation of the data, in particular concerning the structure of the low-lying excited states. Gathering new experimental information, which may reveal the Be-13 structure, is a challenge, particularly in light of its bridging role between Be-12, where the N = 8 neutron shell breaks down, and the Borromean halo nucleus Be-14. The purpose of the present study is to investigate the role of bound excited states in the reaction product Be-12 after proton knockout from B-14, by measuring coincidences between Be-12, neutrons, and gamma rays originating from de-excitation of states fed by neutron decay of Be-13. The Be-13 isotopes were produced in proton knockout from a 400 MeV/nucleon B-14 beam impinging on a CH2 target. The Be-12-n relative-energy spectrum d sigma/dE(fn) was obtained from coincidences between Be-12(g.s.) and a neutron, and also as threefold coincidences by adding gamma rays, from the de-excitation of excited states in Be-12. Neutron decay from the first 5/2(+) state in Be-13 to the 2(+) state in Be-12 at 2.11 MeV is confirmed. An energy independence of the proton-knockout mechanism is found from a comparison with data taken with a 35 MeV/nucleon B-14 beam. A low-lying p-wave resonance in Be-13(1/2(-)) is confirmed by comparing proton- and neutron-knockout data from B-14 and Be-14.

We investigate $\alpha$-like correlations in $^{20}$Ne. A quartet of nucleons (different spin/isospin) is moving in a mean field produced by the $^{16}$O core nucleus. Improving the Thomas-Fermi model (local density approach), a shell model is considered for the core nucleus. The effective potential of the $\alpha$-like quartet and the wave function for the center-of-mass (c.o.m.) motion are calculated and compared with other approaches., Comment: 10 pages, 7 figures. arXiv admin note: substantial text overlap with arXiv:1707.04517

Experimental data on Coulomb breakup and neutron removal indicate that $^{31}\mathrm{Ne}$ is one of the heaviest halo nuclei discovered so far. The possible ground state of $^{31}\mathrm{Ne}$ is either $3/{2}^{\ensuremath{-}}$ coming from the $p$-wave halo or $1/{2}^{+}$ coming from the $s$-wave halo. In this work, we develop a treatable model to include deformed wave functions and a dynamical knockout formalism that includes the dependence on the nuclear orientation to study the neutron removal from $^{31}\mathrm{Ne}$ projectiles at energies around $E\ensuremath{\approx}200$ MeV/nucleon. A detailed account of the effects of deformation on cross sections and longitudinal momentum distributions is made. Our numerical analysis indicates a preference for the $^{31}\mathrm{Ne}$ ground state with spin-parity $3/{2}^{\ensuremath{-}}$.

Quantum phase transitions between competing equilibrium shapes of nuclei with an odd number of nucleons are explored using a microscopic framework of nuclear energy density functionals and a fermion-boson coupling model. The boson Hamiltonian for the even-even core nucleus, as well as the spherical single-particle energies and occupation probabilities of unpaired nucleons, are completely determined by a constrained self-consistent mean-field calculation for a specific choice of the energy density functional and pairing interaction. Only the strength parameters of the particle-core coupling have to be adjusted to reproduce a few empirical low-energy spectroscopic properties of the corresponding odd-mass system. The model is applied to the odd-$A$ Ba, Xe, La, and Cs isotopes with mass $A\ensuremath{\approx}130$, for which the corresponding even-even Ba and Xe nuclei present a typical case of $\ensuremath{\gamma}$-soft nuclear potential. The theoretical results reproduce the experimental low-energy excitation spectra and electromagnetic properties, and confirm that a phase transition between nearly spherical and $\ensuremath{\gamma}$-soft nuclear shapes occurs also in the odd-$A$ systems.

We combine few- and many-body degrees of freedom in a new computationally efficient model applicable to both bound and continuum states and adaptable to different subfields of physics. We formulate a self-consistent three-body model for a core nucleus surrounded by two valence nucleons, where the core is treated in the mean-field approximation and the same effective Skyrme interaction is used between both core and valence nucleons. We apply the model to $^{26}\mathrm{O}$, where we reproduce the known experimental data as well as phenomenological models with more parameters. The decay of the ground state is found to proceed directly into the continuum without effect of the virtual sequential decay through the well-reproduced ${d}_{3/2}$ resonance of $^{25}\mathrm{O}$.

Halo nuclei are weakly bound systems that have a tightly bound core and a small number of weakly-bound valence nucleons. Halo effective field theory is the appropriate framework to describe such systems since it can use this separation of scales between the one-nucleon separation energy of the halo nucleus and the core nucleus to form the expansion parameter in a systematic low-energy expansion. We summarize recent progress in the description of weakly bound systems with halo effective field theory and focus on applications to the one-proton halo nuclei Fluorine-17 and Boron-8.

We measured the reaction cross sections of the two-neutron halo nucleus 14Be with proton and carbon targets at about 41 and 76 MeV/nucleon. Based on a Glauber model calculation, we deduced the matter density distribution of 14Be in which previously measured interaction cross sections at relativistic energies were also included. An s-wave dominance in 14Be has been confirmed, although the halo tail of 14Be is not distributed as much as that of 11Li. Significant mixing of the p-wave in addition to the s- and d-wave is also suggested.

We formulate a core plus few-nucleon model allowing for a rotational excitation of the core. Three and four-body systems including a 12C core nucleus are studied using an explicitly correlated Gaussian basis. Effects of the core excitation are tested by investigating energy levels and electric quadrupole transition probabilities. Though some improvements are obtained, we realize that the Pauli principle for the nucleon-deformable core motion has to be appropriately defined for better understanding.

A comparative analysis of the nucleon stripping and core stripping reactions induced by a halo nucleus is presented on the basis of certain models for diffractive processes. It follows from calculations for the halo nucleus 11Be that the transverse momentum distribution of nucleons for core stripping (as the longitudinal momentum distribution) is less distorted by absorption in a target than the distribution of core fragments for nucleon stripping. The obtained relations between the cross sections for the stripping reactions simplify interpretation of the calculation results.

International audience; The one-neutron removal cross section from 29Ne, 33,35,37Mg, and 39,41Si on a Pb target have been measured at around 240 MeV/nucleon at the RIBF (RI-Beam Factory) at RIKEN. This main goal of the experiment was to extract the inclusive Coulomb breakup cross sections in order to probe possible halo structures through their enhanced low-energy E1 strengths - so-called soft E1 excitations. The results showed significant enhancement of the one-neutron removal Coulomb breakup cross section for 37Mg. This in turn provides evidence for the existence of halo structure in 37Mg.

Background: The ratio method has been proposed as a means to remove the reaction model dependence in the study of halo nuclei. Purpose: Originally, it was developed for higher energies but given the potential interest in applying the method at lower energy, in this work we explore its validity at 20 MeV/nucleon. Method: The ratio method takes the ratio of the breakup angular distribution and the summed angular distribution (which includes elastic, inelastic and breakup) and uses this observable to constrain the features of the original halo wave function. In this work we use the Continuum Discretized Coupled Channel method and the Coulomb-corrected Dynamical Eikonal Approximation for the study. Results: We study the reactions of 11Be on 12C, 40Ca and 208Pb at 20 MeV/nucleon. We compare the various theoretical descriptions and explore the dependence of our result on the core-target interaction. Conclusions: Our study demonstrates that the ratio method is valid at these lower beam energies., Accepted for publication in Phys. Rev. C; 10 pages, 7 figures

The interaction cross sections ( σI ) of the very neutron-rich carbon isotopes 19 C, 20 C and 22 C have been measured on a carbon target at 307, 280, and 235 MeV/nucleon, respectively. A σI of 1.280±0.023 b was obtained for 22 C, significantly larger than for 19,20 C, supporting the halo character of 22 C. A 22 C root-mean-squared matter radius of 3.44±0.08 fm was deduced using a four-body Glauber reaction model. This value is smaller than an earlier estimate (of 5.4±0.9 fm ) derived from a σI measurement on a hydrogen target at 40 MeV/nucleon. These new, higher-precision σI data provide stronger constraints for assessing the consistency of theories describing weakly bound nuclei.

The reaction cross section (σ R σR ) of the very neutron-rich carbon isotope 22 22 C has been measured on a carbon target at 235 MeV/nucleon. A σ R σR of 1.280±0.023 1.280±0.023 b was obtained for 22 22 C, significantly larger than those for the neighboring isotopes, supporting the halo character of 22 22 C. A 22 22 C root-mean-squared matter radius of 3.44±0.08 3.44±0.08 fm was deduced using a four-body Glauber reaction model. This value is smaller than an earlier estimate of 5.4±0.9 5.4±0.9 fm derived from a σ R σR measurement on a hydrogen target at 40 MeV/nucleon.

In present study, we search the lambda magic number in hypernuclei within the framework of relativistic mean field theory (RMF) with inclusion of hyperon-nucleon and hyperon-hyperon potentials. Based on one- and two-lambda separation energy and two-lambda shell gap, 2, 8, 14, 18, 20, 28, 34, 40, 50, 58, 68, 70 and 82 are suggested to be the $\Lambda$ magic number within the present approach. The weakening strength of $\Lambda$ spin-orbit interaction is responsible for emerging the new lambda shell closure other than the model scheme. The predicted $\Lambda$ magic numbers are in remarkable agreement with earlier predictions and hypernuclear magicity quite resembles with nuclear magicity. %Our results also support the nuclear magicity, Our results are supported by nuclear magicity, where neutron number N = 34 is experimentally observed as a magic which is one of the $\Lambda$ closed shell in our predictions. In addition, the stability of hypernuclei is also examined by calculating the binding energy per particle, where Ni hypernucleus is found to be most tightly bound triply magic system in considered hypernuclei. Nucleon and lambda density distributions are observed and it is found that introduced $\Lambda$'s have significant impact on total density and reduces the central depression of the core nucleus. Nucleon and lambda mean field potentials and spin-orbit interaction potentials are also observed for predicted triply magic hypernuclei and the addition of $\Lambda$'s affect the both the potentials to a large extent. The single-particle energy levels are also analyzed to explain the shell gaps for triply magic multi-$\Lambda$ hypernuclei.

Ab initio calculations of nuclei face the challenge of simultaneously describing strong short-range internucleon correlations and the long-range properties of weakly-bound halo nucleons. Natural orbitals, which diagonalize the one-body density matrix, provide a basis which is better matched to the physical structure of the many-body wave function. We demonstrate that the use of natural orbitals significantly improves convergence for ab initio no-core configuration interaction calculations of the neutron halo nucleus 6He, relative to the traditional oscillator basis., 6 pages, 4 figures; presented at the Symposium on Nuclear Dynamics and Thermodynamics, Huizhou, China, December 11, 2016; as published in Nucl. Sci. Tech

Interaction cross sections (sigma(1)) for Me isotopes from the stability line to the vicinity of the neutron drip line have been measured at around 240 MeV/nucleon using BigRIPS at RIBF, RIKEN, The sigma(1) for Ne27-32 in every case exceed the systematic mass-number dependence of sigma(1) for stable nuclei, which can be explained by considering the nuclear deformation. In particular the sigma(1) for Ne-29 and Ne-31 are significantly greater than those of their neighboring nuclides. These enhancements of sigma(1) for Ne-29 and Ne-31 cannot be explained by a single-particle model calculation under the assumption that the valence neutron of Ne-29 (Ne-31) occupies the 0d(3/2) (0f(7/2)) orbital, as expected from the standard spherical shell ordering. The present data suggest an s dominant halo structure of Ne-29 and s- or p-orbital halo in Ne-31. (C) 2011 Elsevier B.V. All rights reserved.

Inclusive halo-nucleus core or nucleon stripping reactions are considered on the basis of a potential three-body model using the eikonal and adiabatic approximations. Clear analytical expressions for the cross sections of these reactions are obtained, and numerical calculations for 11Be halo nucleus are performed. Constituent absorption by the target nucleus substantially influences the integral and differential (with respect to longitudinal momentum) nucleon stripping cross section. It is demonstrated that the differential core stripping cross section contains more complete information on the unperturbed wave function of the halo nucleus.

In order to study the bound-state structure of the Helium halo nuclei, the 8-nucleon Yakubovsky formalism has been implemented for 8He in a 5-body sub-cluster model, i.e. alpha+n+n+n+n. In this case, the 8-nucleon Yakubovsky equations has been obtained in the form of two coupled equations, based on the two independent components. In addition, by removing the contribution interactions of the 8 and 7s bound nucleons in the formalism, the obtained equations explicitly reduce to the 6-nucleon Yakubovsky equations for 6He, in the case of effective 3-body model, i.e. alpha+n+n. In view of the expectation for the dominant structure of 8He, namely an inert alpha-core and four loosely-bound neutrons, Jacobi configurations of the two components in momentum space have been represented to provide technicalities which were considered useful for a numerical performance, such as bound-state calculations and momentum density distributions for halo-bound neutrons.

The halo nucleus nucleon stripping reaction on a light target is studied using the diffraction theory of reactions with weakly bound nuclei. An improved version of the approximation of a small target’s radius (compared to the size of a halo nucleus) is formulated. Simple analytical expressions for the differential cross section and the longitudinal momentum distribution of observed particles that allow us to calculate them with good accuracy are obtained.

The differential cross section for proton scattering on 15N nuclei is calculated within Glauber diffraction theory at energies of 0.2, 0.6, and 1.0 GeV. Use is made of the shell-model wave function for the 15N nucleus. The contribution of single and double collisions to the Glauber operator Ω is taken into account. The sensitivity of the differential cross sections to the contributions of scattering on nucleons from different shells, to the parameters of the elementary pN amplitude, and to the energy of projectile protons is investigated. It is shown that the interference between amplitudes corresponding to different collision multiplicities, as well as between the amplitudes for scattering on nucleons from different shells, determines special features of the cross section.

We study the change in nuclear deformation induced by the presence of one or two lambda hyperons in light and medium-heavy nuclei, comparing Skyrme-Hartree-Fock and relativistic mean field model predictions. The physical origin of the deformation changes is discussed in terms of the lambda and nucleon mean field potentials. We identify 30 Si and 30 S as candidates with possible large deformation differences between the core nucleus and hypernucleus. Subject Index: 206, 211, 214

Assuming a core plus valence nucleon structure, one-nucleon removal reaction is investigated within the framework of few-body Glauber theory. Fermi-type distribution is used for the core density, while the wavefunction of the valence nucleon is calculated by solving the single particle eigenvalue problem of the Schrodinger equation with the Woods-Saxon potential. The parallel momentum distribution (P(parallel to)) of the fragments is calculated for isotopes with 3 < Z < 18. A remarkable scaling property is observed from the dependence of the dimensionless quantity R(v)(2)/R(c)(2) on the full width at half maximum of the parallel momentum distribution (FWHM(P parallel to)). R(v)(2)/R(c)(2) is a measure of the exotic extent of the nuclear halo. Based on the obtained scaling law, FWHM(P parallel to) can be used as an experimental observable to extract R(v)(2)/R(c)(2) and measure the exotic extent for the nuclear halo.

An experimental method based on an analysis of the neutron-neutron correlations in reactions induced by halo nuclei in nuclear photoemulsion is proposed for studying the two-neutron halo structure. Photoemulsion stacks were exposed to a beam of radioactive 6He nuclei. Preliminary data on interaction of the 6He halo nucleus to hydrogen are compared with the results of the kinematic calculation for the reaction of quasi-free proton scattering from clusters making up the 6He halo nucleus. A fraction of quasi-free scattering events with “survival” of the dineutron is evaluated for scattering of protons by the dineutron configuration of the 6He nucleus.

The excited states of some odd A nuclei near the stability line have been systematically investigated from light to intermediate mass with the spherical relativistic mean field (RMF) model. The ratio between the valence nucleon root-mean-square (RMS) radius and the core rms radius, the separation energy and the density distribution have been deduced as signatures for halo or skin structure. We have presented the scaling laws of the ratio of valence particle rms radii and square-potential radii versus the scaled separation energies. The probability for a valence particle being out of the binding potential has also been extracted. We proposed a relaxed necessary condition for nuclear halo occurrence.

Continuum discretised coupled-channels (CDCC) method with a 10Be(0+) + n two-body cluster model is applied to systematically analyze the elastic scattering of the halo nucleus 11Be from the proton target at various incident energies below 100 MeV/nucleon. Using the renormalized 10Be-p potential deduced from the 10Be + p elastic scattering data, the differential cross sections of 11Be + p scattering are well reproduced by the CDCC calculations without any further adjustment parameters, demonstrating the applicability of this approach for describing the scattering of exotic nuclei based on the scattering of the less exotic core nuclei.

The description of nuclei starting from the constituent nucleons and the realistic interactions among them has been a long-standing goal in nuclear physics. In addition to the complex nature of the nuclear forces, with two-, three- and possibly higher many-nucleon components, one faces the quantum-mechanical many-nucleon problem governed by an interplay between bound and continuum states. In recent years, significant progress has been made in ab initio nuclear structure and reaction calculations based on input from QCD-employing Hamiltonians constructed within chiral effective field theory. After a brief overview of the field, we focus on ab initio many-body approaches - built upon the No-Core Shell Model - that are capable of simultaneously describing both bound and scattering nuclear states, and present results for resonances in light nuclei, reactions important for astrophysics and fusion research. In particular, we review recent calculations of resonances in the $^6$He halo nucleus, of five- and six-nucleon scattering, and an investigation of the role of chiral three-nucleon interactions in the structure of $^9$Be. Further, we discuss applications to the $^7$Be$(p,\gamma)^8$B radiative capture. Finally, we highlight our efforts to describe transfer reactions including the $^3$H$(d,n)^4$He fusion., Comment: Contribution to the Special Physica Scripta Edition - 40 year anniversary - Nobel Prize '75, 71 pages, 29 figures

This is an Open Access article distributed under the terms of the Creative Commons Attribution License 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.; International audience; The spectroscopic structure of 19C, a prominent one-neutron halo nucleus, has been studied with a 20C secondary beam at 290 MeV/nucleon and a carbon target. Neutron-unbound states populated by the one-neutron knockout reaction were investigated by means of the invariant mass method. The preliminary relative energy spectrum and parallel momentum distribution of the knockout residue, 19C*, were reconstructed from the measured four momenta of the 18C fragment, neutron, and beam. Three resonances were observed in the spectrum, which correspond to the states at Ex = 0.62(9), 1.42(10), and 2.89(10) MeV. The parallel momentum distributions for the 0.62-MeV and 2.89-MeV states suggest spin-parity assignments of 5/2+ and 1/2−, respectively. The 1.42-MeV state is in line with the reported 5/22+ state.

The inclusive differential cross sections of the 7Li nucleus in a reaction induced by 6He on a 9Be target are measured at an incident energy of 25 MeV/nucleon. Finite-range distorted-wave Born approximation calculations suggest that these 7Li particles are formed in a direct single-proton pickup reaction 9Be(6He,7Li)8Li. The experimental data can be well reproduced by taking into account of the contributions of both the ground states and the first excited states of 7Li and 8Li.

The 17F +p elastic scattering at two near-barrier energies of 3.5 and 4.3 MeV/nucleon, have been analyzed in the framework of the single folding approach. The folded potentials are constructed by folding the density-dependent (DDM3Y) effective nucleon-nucleon interaction over the nuclear density of the one-proton halo nucleus 17F. Two versions of the density are considered. In addition, two versions of the one-nucleon knock-on exchange potentials are introduced to construct the real microscopic potentials. The derived potentials supplemented by phenomenological Woods-Saxon imaginary and spin-orbit potentials produced excellent description of the differential elastic scattering cross sections at the higher energy without need to introduce any renormalization. At the lower energy, however, in order to successfully reproduce the data, it is necessary to reduce the strength of the constructed real DDM3Y potential by about 25% of its original value. Furthermore, good agreement with data is obtained using the extracted microscopic DDM3Y potentials for both real and imaginary parts. Moreover, the interesting notch test is applied to investigate the sensitivity of the elastic scattering cross section to the radial distribution of the constructed microscopic potentials. The extracted reaction (absorption) cross sections are, also, investigated.

Background: Resonances with pronounced single-particle characteristics are crucial for quantitative descriptions of exotic nuclei near and beyond the drip lines, and often impact halo formation and nucleon decay processes. Since the majority of nuclei are deformed, the interplay between deformation and orbital structure near threshold can lead to improved descriptions of exotic nuclei.Purpose: Develop a method to study single-particle resonant orbital structure in the Dirac equation with a quadrupole-deformed Woods-Saxon potential. Determine the structure evolution of bound and resonant levels with deformation in this scheme, and examine the impact on halo formation in loosely bound systems, with a focus on the recent halo candidate nucleus $^{37}\mathrm{Mg}$.Method: Analytical continuation of the coupling constant (ACCC) method is developed on the basis of the Dirac equation with a deformed Woods-Saxon potential. The scalar and vector terms in the deformed potential are determined by the energies of the valence neutron and nearby orbitals, which are extracted from a self-consistent relativistic Hartree-Bogoliubov (RHB) calculation with the PC-PK1 density functional.Results: We compare the energies and widths of resonant orbitals in the recent halo nucleus candidate $^{37}\mathrm{Mg}$ using the ACCC method based on the Dirac coupled-channel equations with those determined from the scattering phase shift (SPS) method. It is found that the results from the two methods agree well for narrow resonances, whereas the SPS method fails for broad resonances. Nilsson levels for bound and resonant orbitals from the ACCC method are calculated over a wide range of deformations and show some decisive hints of halo formation in $^{37}\mathrm{Mg}$.Conclusions: In our ACCC model for deformed potentials in the coupled-channel Dirac equations, the crossing of the configuration $1/2[321]$ and $5/2[312]$ orbitals at a deformation of approximately 0.5 enhances the probability to occupy the $1/2[321]$ orbital coming from $2{p}_{3/2}$ thereby explaining the recent observation of a $\mathit{p}$-wave one-neutron halo configuration in $^{37}\mathrm{Mg}$. The resonant $1/2[301]$ configuration plays a crucial role in halo formation in the magnesium isotopes beyond $A=40$ for a wide range of deformations larger than 0.2.

Coulomb breakup of the two-neutron halo nucleus 11Li has been investigated in a kinematically complete measurement of three-body breakup of 11Li on a Pb target at approximately 70 MeV/nucleon at RIKEN. Cross-talk events have been excluded without affecting the efficiency very much up to very low relative energy. The resultant preliminary B(E1) spectrum has revealed high (E1) strength at Erel (three-body relative energy) ~0.3 MeV, which was missing in the previous measurements. This E1 strength with the help of the E1 cluster sum-rule indicates a significant neutron–neutron correlation in the ground state of 11Li.

Differential cross sections for quasi-elastic scattering, breakup reaction as well as 1n- and 2n-transfer reactions induced by 6He at 25 MeV/nucleon from a 9Be target are reported. The experimental data were analysed in the context of the coupled-channel calculations. The internal structure of 6He is discussed and further studies are proposed.

The capture cross sections at stellar energies are very difficult to measure directly. Hence, data are usually evaluated by using indirect methods or extrapolations from the experimental data obtained at the lowest possible energies. The asymptotic normalization coefficient (ANC) approach of the transfer reactions provides a reliable way for the determination of the capture cross sections at stellar energies. By virtue of its reliability, we have calculated the capture cross sections of the 10Be(n,γ)11Be reaction by using nuclear ANC method. 11Be is a well-known neutron halo nucleus with two weakly bound states. As a typical example, we have shown that the radiative cross sections for a nucleon captured into a halo state are obviously enhanced. The enormous enhancement of the capture cross section is just due to the large overlap of the incident neutron wave with the extended tail of the halo. The 10Be(n,γ)11Be capture reaction is involved in the inhomogeneous big-bang nucleosynthesis. We have evaluated its reaction rates at stellar energies with the nuclear ANC method.

The high-spin states of 93Mo have been studied by a 82Se( 16O, 5n) 93Mo reaction at a beam energy of 100 MeV using techniques of in-beam γ-ray spectroscopy. Measurements of γ-t, γ-γ-t coincidences, γ-ray angular distributions and γ-ray linear polarizations were performed. The high-spin isomer was found as a (39/2-) state at about 9.7 MeV. The near-yrast states in 93Mo were interpreted using the weak-coupling picture of a d5/2 neutron to a neutron magic core nucleus 92Mo.

The relativistic mean field (RMF) model is applied to a system of nucleons and a $\bar K$ meson, interacting via scalar and vector boson fields. The model incorporates the standard RMF phenomenology for bound nucleons and, for the $\bar K$ meson, it relates to low-energy ${\bar K}N$ and $K^-$ atom phenomenology. Deeply bound $\bar K$ nuclear states are generated dynamically across the periodic table and are exhibited for $^{12}$C and $^{16}$O over a wide range of binding energies. Substantial polarization of the core nucleus is found for these light nuclei. Absorption modes are also included dynamically, considering explicitly the reduced phase space for $\bar K$ absorption from deeply bound states. The behavior of the calculated width as function of the $\bar K$ binding energy is studied in order to explore limits on the possible existence of narrow $\bar K$ nuclear states., 12 pages, 1 table, 3 figures Minor changes, to appear in PLB

The breakup of a one-neutron halo nucleus is studied in the eikonal approximation. Both the nuclear and Coulomb breakup processes are taken into account. The continuum states, which are usually approximated by plane waves, are constrained to satisfy the condition of orthogonality to the bound states of the halo nucleus. Taking full account of the recoil effect, the neutron-core relative energy distributio no f the breakup cross section is calculated for 11 Be and 19 C projectiles incident on 12 Ca nd 208 Pb targets and compared to experimental data. All the data regarding the energy distribution for a 208 Pb target at beam energies of 68 and 520 MeV/nucleon are accurately reproduced, except for its peak at small relative energy. The experimental data regarding the relative energy distribution for the 11 Be+ 12 C system are also accurately reproduced. It is shown that use of orthogonalized plane waves leads to reduced cross sections and is necessary to account for the experimental data. The effect of the no-recoil limit is quantified.