Neutron Halo Nuclei Research Articles

Study of Nuclear Structure and Elastic Electron Scattering Form Factors for Neutron Halo Nuclei (22N ,23O and 24F) Using Full Correlation Functions with Two Size Parameters

The study of neutron-rich nuclei's form factors, root-mean-square radius (rms), and nuclear density distributions is the focus of this work for the nuclei (22N,23 O and 24F). With the use of a strong short-range effect and a strong tensor force, the nucleons distribution function of the two oscillating harmonic particles in a two-frequency shell model operates with two different parameters: the first (bcore), for the inner (core) orbits, and the second (bvalence) for the outer (halo) orbits. This work demonstrated the existence of neutron halo nuclei for the nuclei (22N, 23O and 24F) in the (2s1/2) shell. The computed density distribution of neutron, proton and matter for these nuclei displayed the long tail performance. Using the Borne approximation of the plane wave, the elastic form factor of the electron scattering from the alien nucleus was calculated, this form factor is independent of the neutrons that make up the halo, but rather it results from a difference in the proton density distribution of the last proton in the nuclei. Fortran 95 power station program was used to the neutron, proton and matter density, elastic electron scattering form factor, and rms radii. The calculated outcomes for these exotic nuclei were in good agreement with the experimental data.

Theoretical study on neutron halo emission from heavy elements

Theoretical study on the emission characteristics of one-neutron and two-neutron halo nuclei from heavy elements was performed within the framework of the Unified Description formula (UD), Universal Decay Law (UDL), Modified Universal Decay Law (MUDL), Gupta formula, Ren formula and the formula of Horoi et al. The predictions are compared with that of the Coulomb and Proximity Potential Model (CPPM) of Santhosh et al. [6]. One neutron halo nuclei 15C, 23O, and 24F are found to be emitted from heavy elements with a half-life within the experimental upper limit. Compared to one-neutron halo, two-neutron halo emissions are less probable to emit from heavy elements. The UDL and MUDL are found to be the most successful empirical formulae in describing the halo decay characteristics of heavy elements.

Fusion reactions in collisions of neutron halo nuclei with heavy targets

Fusion reactions in collisions of neutron halo nuclei with heavy targets

Breakup of the proton halo nucleus 8B near barrier energies

The dynamics of a nuclear open quantum system could be revealed in the correlations between the breakup fragments of halo nuclei. The breakup mechanism of a proton halo nuclear system is of particular interest as the Coulomb polarization may play an important role, which, however, remains an open question. Here we use a highly efficient silicon detector array and measure the correlations between the breakup fragments of 8B incident on 120Sn at near-barrier energies. The energy and angular correlations can be explained by a fully quantum mechanical method based on the state-of-the-art continuum discretized coupled channel calculations. The results indicate that, compared to the neutron halo nucleus 6He, 8B presents distinctive reaction dynamics: the dominance of the elastic breakup. This breakup occurs mainly via the short-lived continuum states, almost exhausts the 7Be yield, indicating the effect of Coulomb polarization on the proton halo state. The correlation information reveals that the prompt breakup mechanism dominates, occurring predominantly on the outgoing trajectory. We also show that, as a large environment, the continuum of 8B breakup may not significantly influence elastic scattering and complete fusion.

Effect of different nucleon–nucleon interactions based on relativistic mean field theory on elastic scattering cross-sections of proton and neutron halo nuclei

Effect of different nucleon–nucleon interactions based on relativistic mean field theory on elastic scattering cross-sections of proton and neutron halo nuclei

Evidence of a Near-Threshold Resonance in ^{11}B Relevant to the β-Delayed Proton Emission of ^{11}Be.

A narrow near-threshold proton-emitting resonance (E_{x}=11.4 MeV, J^{π}=1/2^{+}, and Γ_{p}=4.4 keV) was directly observed in ^{11}B via proton resonance scattering. This resonance was previously inferred in the β-delayed proton emission of the neutron halo nucleus ^{11}Be. The good agreement between both experimental results serves as a ground to confirm the existence of such exotic decay and the particular behavior of weakly bound nuclei coupled to the continuum. R-matrix analysis shows a sizable partial decay width for both, proton and α (Γ_{α}=11 keV) emission channels.

Natural orbitals for theab initiono-core configuration interaction approach

Ab initio no-core configuration interaction (NCCI) calculations for the nuclear many-body problem have traditionally relied upon an antisymmetrized product (Slater determinant) basis built from harmonic oscillator orbitals. The accuracy of such calculations is limited by the finite dimensions which are computationally feasible for the truncated many-body space. We therefore seek to improve the accuracy obtained for a given basis size by optimizing the choice of single-particle orbitals. Natural orbitals, which diagonalize the one-body density matrix, provide a basis which maximizes the occupation of low-lying orbitals, thus accelerating convergence in a configuration-interaction basis, while also possibly providing physical insight into the single-particle structure of the many-body wave function. We describe the implementation of natural orbitals in the NCCI framework and examine the nature of the natural orbitals thus obtained, the properties of the resulting many-body wave functions, and the convergence of observables. After taking ${}^{3}\mathrm{He}$ as an illustrative testbed, we explore aspects of NCCI calculations with natural orbitals for the ground state of the $p$-shell neutron halo nucleus ${}^{6}\mathrm{He}$.

Study of cluster emissions from heavy nuclei using an empirical formula and the Coulomb and Proximity potential model for deformed nuclei

The decay characteristics of various clusters and neutron halo nuclei from heavy elements [Formula: see text] are studied within the framework of the Coulomb and Proximity Potential Model for Deformed Nuclei (CPPMDN) and using a new empirical formula proposed by us. The predictive power of our formula is verified by comparing the predictions with the available experimental data and with the predictions of other models such as CPPM, Universal Decay Law of Qi et al. (UDL), Unified Description formula (UD) of Ni et al. Using the present formula and CPPMDN, decay half-lives of various light clusters from heavy elements are calculated, and the results are compared with the predictions of UDL, UD, and predictions made by Santhosh et al. based on the Modified Generalized Liquid Drop Model (MGLDM). The decay half-lives of halo nuclei from heavy elements are also calculated using the new formula and CPPMDN and compared with the predictions of UDL, UD, and the predictions made by Santhosh et al. based on the Coulomb and Proximity Potential Model (CPPM).

Fusion Reaction Study of some Selected Halo Systems

The challenge in studying fusion reaction when the projectile is neutron or proton rich halo nuclei is the coupling mechanism between the elastic and the breakup channel, therefore the motivation from the present calculations is to estimate the best coupling parameter to introduce the effect of coupled-channels for the calculations of the total cross section of the fusion , the barrier distribution of the fusion and the average angular momentum 〈L〉 for the systems 6He+206Pb, 8B+28Si, 11Be+209Bi, 17F+208Pb, 6He+238U, 8He+197Au and 15C+232Th using quantum mechanical approach. A quantum Coupled-Channel Calculations are performed using CC code. The predictions of quantum mechanical approach are comparable with the measured data that is available. Above and below the Coulomb barrier, comparison of theoretical calculations of quantum mechanical with the relevant measured data demonstrates good agreement.

Probing proton halo effects in the 8B+64Zn collision around the Coulomb barrier

Proton halo effects in the 8B+64Zn reaction at an energy around 1.5 times the Coulomb barrier have been studied at HIE-ISOLDE CERN using, for the first time, the only existing postaccelerated 8B beam. This, together with the use of a high granularity and large solid angle detection system, allowed for a careful mapping of the elastic angular distribution, especially in the Coulomb-nuclear interference region. Contrary to what is observed for the one-neutron halo nucleus 11Be on the same target in a similar energy range, the analysis of the elastic scattering angular distribution shows only a modest suppression of the Coulomb-nuclear interference peak, with no remarkable enhancement of the total reaction cross-section. Inclusive angular and energy distributions of 7Be produced in direct reaction processes have also been measured. The comparison of these data with the results of theoretical calculations for the elastic and non-elastic breakup contributions indicate that both processes are important. Overall, the experimental data suggest a 8B collision dynamics at the barrier very different from the one of neutron halo nuclei, showing only modest effects of coupling to continuum. This behaviour can be interpreted as due to the presence of the additional Coulomb interactions halo-core and halo-target together with the presence of the centrifugal barrier felt by the valence proton of 8B.

Influence of halo single-neutron transfer on near barrier ^{15}C + ^{12}C total fusion

A recent comparison of the average fusion cross section, leftlangle sigma _mathrm {F}rightrangle , for energies just above the Coulomb barrier for the ^{12-15}C + ^{12}C systems found that the behaviour as a function of projectile neutron excess could not be satisfactorily explained by static barrier penetration model calculations and suggested that the neutron dynamics plays an important rôle. In this work we demonstrate that the (^{15}C,^{14}C) single neutron transfer has a significant influence on the above barrier ^{15}C + ^{12}C total fusion, although not quite in the way expected since it leads to a reduction in the cross section, contrary to the trend in the measured leftlangle sigma _mathrm {F}rightrangle . However, this result underlines the danger of ignoring the effect of neutron transfer reactions on fusion in systems involving neutron halo nuclei.

Elastic scattering angular distributions of neutron halo nucleus $$^{11}$$Be studied via dynamic polarization potentials

Cluster aspects of the nuclear structure manifest themselves in, among many other types of nuclear reactions, the breakup reactions of weakly-bound nuclei and their couplings with the other reaction channels. In the present work we analyzed the breakup coupling effects to the elastic scattering angular distributions of $$^{11}$$ Be with a $$^{208}$$ Pb target at an incident energy of 140 MeV. Weighted mean local polarization potentials (WMLPPs), which mimic the dynamic polarization potentials (DPPs) induced by the breakup coupling effects to the elastic scattering channel, were obtained from continuum discretized coupled channel (CDCC) calculations. Suppression of the Coulomb-nuclear interference peaks (CNIPs) of the elastic scattering angular distributions is found to be caused by the destructive interference between the Coulomb and the Coulomb-distorted nuclear amplitude due to the WMLPPs. Comparisons between the WMLPPs and the theoretically calculated Coulomb dipole polarization potentials (CDPPs) suggest that the breakup coupling effect of the $$^{11}$$ Be+ $$^{208}$$ Pb system cannot be represented by the CDPPs alone.

Scattering of the halo nucleus 11Be from a lead target at 3.5 times the Coulomb barrier energy

Angular distributions of quasielastic scattering and breakup of the neutron-rich halo nucleus 11Be on a 208Pb target at an incident energy of 140 MeV (about 3.5 times the Coulomb barrier) were measured at HIRFL-RIBLL. A strong suppression of the Coulomb nuclear interference peak is observed in the measured quasielastic scattering angular distribution. The result demonstrates for the first time the persistence of the strong breakup coupling effect reported so far for reaction systems involving neutron-halo nuclei at this relatively high incident energy. The measured quasielastic scattering cross sections are satisfactorily reproduced by continuum discretized coupled channel (CDCC) calculations as well as by the XCDCC calculations where the deformation of the 10Be core is taken into account. The angular and energy distributions of the 10Be fragments could also be well reproduced considering elastic breakup (CDCC and XCDCC) plus nonelastic breakup contributions, with the latter evaluated with the model by Ichimura, Austern and Vincent [1]. The comparison of the 10Be energy distributions with simple kinematical estimates evidence the presence of a significant post-acceleration effect which, in the (X)CDCC frameworks, is accounted for by continuum-continuum couplings.

Assessment of the beta-delayed proton decay rate of 11Be

The 11Be neutron halo nucleus appears to decay into 10Be with a rate that exceeds expectations. Neutron disappearance into dark matter, beta decay of a halo neutron, or beta-delayed proton decay have been offered as explanations. In this work we study the latter option; we carry out shell model calculations and sequential decay analysis examining the beta-delayed proton decay going through a resonance in 11B. The narrow energy window, lack of states with sufficient spectroscopic strength, overwhelming alpha decay branch, all make reconciling the observed rate with beta-delayed proton decay difficult.

Finite-size effects in heavy halo nuclei from effective field theory

Halo/Cluster Effective Field Theory describes halo/cluster nuclei in an expansion in the small ratio of the size of the core(s) to the size of the system. Even in the point-particle limit, neutron-halo nuclei have a finite charge radius, because their center of mass does not coincide with their center of charge. This point-particle contribution decreases as 1/A_mathrm {c}, where A_mathrm {c} is the mass number of the core, and diminishes in importance compared to other effects, e.g., the size of the core to which the neutrons are bound. Here we propose that for heavy cores the EFT expansion should account for the small factors of 1/A_mathrm {c}. As a specific example, we discuss the implications of this organizational scheme for the inclusion of finite-size effects in expressions for the charge radii of halo nuclei. We show in particular that a short-range operator could be the dominant effect in the charge radius of one-neutron halos bound by a P-wave interaction. The point-particle contribution remains the leading piece of the charge radius for one-proton halos, and so Halo EFT has more predictive power in that case.

Soft giant resonance in two neutron halo nucleus 11Li

Lithium-11 is a showcase of neutron halos and has been providing new insight to nuclear structure researches. Recently, an isoscalar resonance at low excitation energy ($ E_\mathrm{x} \sim 1$ MeV) has been confirmed by the development of a low-energy high-intensity beam of 11Li at TRIUMF. By inelastic scattering measurements $ (\mathrm{p}, \mathrm{p}^{\prime})$ and $ (\mathrm{d}, \mathrm{d}^{\prime})$ with inverse kinematics, the first excited state of 11Li has been studied in detail and an isoscalar nature of the transitions has been confirmed and a strong transition amplitude has been observed indicating the soft-resonance of 11Li. Those recent experimental results on the excitation of the soft resonance are described and then recent theoretical developments based on the four-body continuum-discretized coupled-channels 11Li + p system are presented together with a brief history of the resonance search in 11Li.

Effects of pairing, continuum, and deformation on particles in the classically forbidden regions for Mg isotopes

Particles in the classically forbidden regions are studied based on the deformed relativistic Hartree-Bogoliubov theory in continuum with PC-PK1 for magnesium isotopes. By analyzing the neutron and proton radii, it is found that the largest deviations from the empirical values appear at the predicted neutron halo nuclei $^{42}$Mg and $^{44}$Mg. Consistently, notable increases at $^{42}$Mg and $^{44}$Mg are found in the total number of neutrons in the classically forbidden regions that includes the number of neutrons in continuum. It is shown that the deformation effect, in general, increases the number of particles in the classically forbidden regions below the continuum threshold. The most deeply bound single-particle states play the dominant roles in the increase caused by deformation.

Existence of 15-21N, 17-23O, and 19-25F Neutron Halo Nuclei via Cluster Decay Process in the Superheavy Region

The barrier penetrability and half-life for the decay of neutron halo nuclei 15-21N, 17-23O, and 19-25F from even–even nuclei with Z = 116, 118, and 120 have been determined using the Coulomb and Proximity Potential Model. The studies revealed that the neutron shell closure occurs, in super heavy region, at neutron numbers 164, 178, 184, and 192. The half-life of decay is found to be minimum for the decay of 15N, 20O, and 23F which results in the formation of daughter nuclei with neutron numbers 184, 180, and 178, respectively. The introduction of nuclear deformation caused a decrease in the half-life of decay for axially symmetric combination of parent–daughter–halo nuclei.

Proton- and neutron-halo breakups: Similarities and differences

It is shown in this paper that the decrease of the projectile ground state binding energy in a neutron-halo nucleus and the removal of the Coulomb barrier in the proton-halo nucleus, produce a similar qualitative effect on the elastic scattering cross sections. The variation of the binding energy produces opposite effects on elastic scattering and breakup cross sections. A strongly destructive Coulomb-nuclear interference owing to the decrease of the binding energy is also obtained.

Theoretical Study on Carbon Isotopes

This work is devoted to develop nuclear matter density distribution form for the heavy ions valid for the stable and halo nuclei. In this study we consider the neutron halo nuclei (15,17,19C) and (16,22C). The first group has a 1n-halo while the second has a 2n-halo. Based on the developed densities, the elastic scattering cross section data of C-isotopes on target of 12C, at incident energies 70.8, 78 and 106.9 MeV/N, have been analyzed within the energy density functional theory. A consistent structural study of the neutron drip–line 22 C nucleus is done.