Halo Nucleus 11Be Research Articles

Study on the decay of Z = 127 – 132 superheavy nuclei via emission of 1-n and 2-n halo nuclei

The barrier penetrability, decay constant and decay half-life of 1-n halo nuclei 11Be, 15,17,19C, 22N, 23O, 24,26F, 29,31Ne, 34,37Na, 35,37Mg, and 55Ca; and 2-n halo nuclei 22C, 27,29F, 34Ne, 36Na, and 46P from Z = 127 – 132 parents were calculated within the framework of the Coulomb and proximity potential model by calculating the Q-values using the finite-range droplet model. A comparison between the decay half-lives is made by considering the halo candidates as a normal cluster and as a deformed structure with a rms radius. Neutron shell closure at 190, 196, 198, 200, 204, and 208 are identified from the plot of decay half-lives versus the neutron number of daughter nuclei (NP). The calculation of alpha decay half-life and spontaneous decay half-life showed that the majority of the parent nuclei survive spontaneous fission and decay through alpha emission. The Geiger-Nuttall plots of log10T1/2 versus Q-1/2 and universal plots of log10T1/2 versus -lnP for the emission of all 1-n and 2-n halo nuclei from the parents considered here are linear and show the validity of Geiger - Nuttall law in the case of decay of halo nuclei from superheavy elements.

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

The 8B+64Zn reaction at 38.5 MeV has been studied at HIE-ISOLDE CERN to investigate proton halo effect on the reaction dynamics. For the first time it was used the only existing post-accelerated 8B beam. The measured elastic scattering angular distribution showed a small suppression of the Coulomb-nuclear interference peak, opposite to what observed for the one-neutron halo nucleus 11Be on the same target where a large suppression was observed instead. Inclusive angular and energy distributions of breakup fragments were also measured showing that, both, elastic and non-elastic breakup contribute. The presence of the additional Coulomb interactions halo-core and halo-target in 8B makes the reaction dynamics in this proton-halo nucleus different than the neutron-halo case.

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.

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.

Insights into the dynamics of breakup of the halo nucleus 11Be on a 64Zn target

We reexamine the elastic and breakup observables of the Be11+64Zn reaction at the near-barrier energy of 28.7 MeV. The measured quasi-elastic data are compared with CDCC and extended CDCC (XCDCC) calculations, the latter including the effect of the 10Be deformation.The angular distribution of emitted 10Be fragments, reported in the original analysis of this experiment, along with newly extracted 10Be energy distributions, are compared with calculations for the elastic breakup and non-elastic breakup contributions. Elastic breakup, computed with CDCC, accounts for most of the observed yields. The remaining difference (∼20%) is attributed to non-elastic breakup events (neutron absorption or target excitation) as confirmed by calculations performed with the model of Ichimura, Austern and Vincent (1985) [14].Finally, the effect of post-acceleration in the energy distribution is investigated. This effect is well accounted for by the present CDCC calculations and, according to simple kinematical considerations, is estimated to be of the order of 1 MeV, and roughly independent of the scattering angle.

Reliable extraction of the dB(E1)/dE for 11Be from its breakup at 520 MeV/nucleon

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.

Structure and reactions of N=7 isotones: parity inversion and transfer processes

The interplay of particle and vibrations in N=7 isotones is considered according to nuclear field theory, focusing on the main many-body effects which renormalise the energy spectrum of the halo nucleus 11Be, leading to parity inversion and to renormalization of the form facto s determining the cross sections associated with one-nucleon transfer reactions.

Extraction of the ANC from the 10Be(d, p)11Be transfer reaction using the ADWA method

A halo nucleus is built from a core and at least one weakly bound neutron or proton. To understand this unique cluster structure, lots of efforts have been undertaken. During the past decades, the (d, p) reaction has been widely used in experiments and has become an important tool for extracting single-particle properties of nuclei. In this work, our goal is to obtain the Asymptotic Normalization Coefficient (ANC) of the halo nuclei 11Be using the ADWA method. We perform the analysis for the 10Be(d, p)11Be stripping reaction at Ed=21.4, 18, 15, and 12MeV for the ground state and first excited state of the composite nucleus 11Be. The experimental measurement was carried out at Oak Ridge National Laboratory by Schmitt et al. [1] The sensitivity of the calculations to the optical potential choice is also checked. Overall, the transfer process becomes more peripheral at lower energies and forward angles. Investigation in this area is the best way to extract a reliable ANC from the experimental data. For the ground state of 11Be, the ANC obtained using our method shows perfect agreement with the one obtained by Ab initio calculations (CAb=0.786 fm−1/2) [2].

Analysis of 11Be + p elastic scattering using a BHF approach

The elastic scattering of the halo nucleus 11Be on the proton at various incident energies has been analysed using the microscopic optical potential (OP) calculated within the first order non-relativistic Brueckner–Hartree–Fock (BHF) approach. Argonne v-18 inter-nucleon potential is employed to calculate the microscopic OP. The nuclear density distribution has been obtained using a semi-phenomenological model. The density used shows extended neutron distribution indicating a possible halo structure. We have also compared our results with an empirical analysis using CH89 global OP. The analysis reveals that the BHF approach provides good agreement with the experimental data for all incident energies considered in this paper.

Systematic CDCC calculations for 11Be + p elastic scattering

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.

Double folding model analysis of elastic scattering of halo nucleus 11Be from 64Zn

Calculations of elastic scattering cross-sections for 9,10,11Be + 64Zn at near-Coulomb barrier energy have been performed using a potential obtained from the double folding model and are compared with the experiment. In the framework of the double folding model, the nuclear matter densities of 9,10,11Be projectiles and a 64Zn target are folded with the complex energy-dependent effective M3Y interaction. The angular distributions of the differential cross-section for 9,10Be scattering from 64Zn at E c.m≈ 24.5 MeV agree remarkably well with the data, while in case of 11Be, calculations show a Coulomb–nuclear interference peak which is not observed in the data.

Reactions of a10Be beam on proton and deuteron targets

The extraction of detailed nuclear structure information from transfer reactions requires reliable, well-normalized data, as well as optical potentials and a theoretical framework demonstrated to work well in the relevant mass and beam energy ranges. It is rare that the theoretical ingredients can be tested well for exotic nuclei owing to the paucity of data. The halo nucleus 11Be has been examined through the 10Be(d,p) reaction in inverse kinematics at equivalent deuteron energies of 12,15,18, and 21.4 MeV. Elastic scattering of 10Be on protons was used to select optical potentials for the analysis of the transfer data. Additionally, data from the elastic and inelastic scattering of 10Be on deuterons was used to fit optical potentials at the four measured energies. Transfers to the two bound states and the first resonance in 11Be were analyzed using the finite-range adiabatic wave approximation. Consistent values of the spectroscopic factor of both the ground and first excited states were extracted from the four measurements, with average values of 0.71(5) and 0.62(4), respectively. The calculations for transfer to the first resonance were found to be sensitive to the size of the energy bin used and therefore could not be used to extract a spectroscopic factor.3 MoreReceived 2 October 2013Revised 13 November 2013DOI:https://doi.org/10.1103/PhysRevC.88.064612©2013 American Physical Society

Relations between the differential cross sections for diffractive processes of nucleon stripping and halo-nucleus core stripping

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.

Halo NucleusBe11: A Spectroscopic Study via Neutron Transfer

The best examples of halo nuclei, exotic systems with a diffuse nuclear cloud surrounding a tightly bound core, are found in the light, neutron-rich region, where the halo neutrons experience only weak binding and a weak, or no, potential barrier. Modern direct-reaction measurement techniques provide powerful probes of the structure of exotic nuclei. Despite more than four decades of these studies on the benchmark one-neutron halo nucleus 11Be, the spectroscopic factors for the two bound states remain poorly constrained. In the present work, the 10Be(d,​p) reaction has been used in inverse kinematics at four beam energies to study the structure of 11Be. The spectroscopic factors extracted using the adiabatic model were found to be consistent across the four measurements and were largely insensitive to the optical potential used. The extracted spectroscopic factor for a neutron in an nℓj=2s(1/2) state coupled to the ground state of 10Be is 0.71(5). For the first excited state at 0.32 MeV, a spectroscopic factor of 0.62(4) is found for the halo neutron in a 1p(1/2) state.

Electric dipole response of halo nuclei

Characteristic features of electric dipole transitions at low excitation energies (soft E1 excitation) for halo nuclei are presented. Energy spectra of soft E1 excitations in the one neutron halo nucleus 11Be and in the two neutron halo nucleus 11Li using the Coulomb breakup reactions are shown, which illustrate the mechanism of the soft E1 excitation in these cases. We also show recent experimental results on inclusive Coulomb breakup performed at the new-generation RI beam facility, RIBF, at RIKEN. There, we have obtained evidence for halo structure in the very neutron rich nucleus 31Ne, which is the heaviest halo ever known.

Isotope shift measurements in the 2s1/2 → 2p3/2 transition of Be+ and extraction of the nuclear charge radii for 7, 10, 11Be

We have performed isotope shift measurements in the 2s1/2 → 2p3/2 transition of Be+ ions using advanced collinear laser spectroscopy with two counter-propagating laser beams. Measurements involving a frequency comb for laser stabilization and absolute frequency determination allowed us to determine the isotope shifts with an accuracy of 2 MHz. From the isotope shifts between 9Be and 7, 10, 11Be, high-accuracy mass shift calculations and the charge radius of the reference isotope 9Be we determined nuclear charge radii for the isotopes 7, 10Be and the one-neutron halo nucleus 11Be. The results are compared to nuclear-structure calculations using the fermionic molecular dynamics model which reproduce well the general trend of the radii. Decreasing charge radii from 7Be to 10Be are explained by the cluster structure of the nuclei. The increase from 10Be to 11Be is mainly caused by the halo neutron by which the 10Be core moves relative to the center of mass. Polarization of the 10Be core has only a small influence on the charge radius.

Reaction mechanisms for weakly-bound, stable nuclei and unstable, halo nuclei on medium-mass targets

An experimental overview of reactions induced by the stable, but weakly-bound nuclei 6Li, 7Li and 9Be, and by the exotic, halo nuclei 6He, 8B, 11Be and 17F on medium-mass targets, such as 58Ni, 59Co or 64Zn, is presented. Existing data on elastic scattering, total reaction cross sections, fusion processes, breakup and transfer channels are discussed in the framework of a CDCC approach taking into account the breakup degree of freedom.

Isotope shift measurements of 11, 9, 7Be+

We have performed precision atomic spectroscopy of trapped radioactive Be isotopes aiming at studies of the charge and magnetization radii of these nuclei especially for a single-neutron halo nucleus 11Be . Some experimental results and the status of the analysis are discussed.

Deuteron stripping and pickup involving the halo nucleiBe11andC15

Three-body calculations of (d,p) and (p,d) reactions involving one-neutron halo nuclei 11Be and 15C are performed using the framework of Faddeev-type scattering equations. Important effects of the optical potential nonlocality are found improving the description of the experimental data. The obtained values for the neutron spectroscopic factor are consistent with estimations from other approaches.

Scattering of 11Be halo nucleus from 209Bi at the Coulomb barrier

The scattering of the radioactive, weakly bound, halo nucleus 11Be from 209Bi has been studied at 40MeV beam energy. The measurement performed with a low-intensity and a large-emittance secondary beam could be made using an extremely compact, large solid angle (∼ 2π sr) detecting set-up, based on 8 highly segmented Si telescopes. The 11, 9Be scattering angular distributions, as well as their relative reaction cross-sections, resulted to be rather similar. This may suggest that at Coulomb barrier energies the halo structure and the very small binding energy of the 11Be projectile have no big influence on the reaction dynamics.