Neutron Halo Nuclei Research Articles

Special roles of loose neutron-halo nucleus structure on the fragmentation and momentum dissipation in heavy ion collisions

We studied the special roles of loose neutron-halo structure of 19B on the fragmentation and momentum dissipation by using isospin dependent quantum molecular dynamics. In order to protrude the special roles of neutron-halo structure on the reaction dynamics we compared the fragmentation multiplicity and nuclear stopping (momentum dissipations) induced by neutron-halo nucleus 19B with those induced by a same mass stable nucleus 19F under the same incident channel condition. We found that the loose neutron-halo structure of 19B increases the fragmentation multiplicity in lower beam energy region. On the contrary, the special halo structure of 19B weakens the nuclear stopping, compared to those induced by stable nucleus 19F. However both fragmentation multiplicity-difference and nuclear stopping-difference between the reactions induced by 19B and 19F gradually decrease and finally disappear as the increase of beam energy. These results suggest a good project for the experimental measurements of the fragmentation multiplicity and nuclear stopping to study the reaction dynamics induced by neutron-halo nuclei.

Coulomb and nuclear breakup of halo nuclei

Breakup Reactions have been experimentally investigated for the one neutron halo nucleus 11Be and the two neutron halo nucleus 11Li at about 70 MeV/nucleon at RIKEN. We here focus on the breakup with a Pb target, where the Coulomb breakup is dominant over nuclear breakup, and its soft E1 excitation has been a central issue. For 11Be, we present the energy spectra analyzed with the inelastic scattering angle. The selection at very forward angles has been used to extract the E1 strength, which is then applied to obtain the spectroscopic factor of the halo ground state. For 11Li, we have observed significant E1 strength at very low relative energies, which were missing in the previous measurements.

Tensor correlation in neutron halo nuclei

We investigate the effect of the tensor correlation on the light neutron-rich nuclei. We extend the model space of 4He core with the shell model approach to incorporate the tensor correlation, and π-like 0− particle-hole correlation is strongly favored. This affects the LS splitting in 5He and the 0+2 state of 6He. We also investigate that the tensor correlation is suppressed in 11Li for p2 configuration of last two neutrons, which naturally mixes the s2 component in the ground state and produces the halo structure.

Effective-Range Approach and Scaling Laws for Electromagnetic Strength in Neutron-Halo Nuclei

We study low-lying multipole strength in neutron-halo nuclei. The strength depends only on a few low-energy constants: the neutron separation energy, the asymptotic normalization coefficient of the bound-state wave function, and the scattering length that contains the information on the interaction in the continuum. The shape of the transition probability shows a characteristic dependence on few scaling parameters and the angular momenta. The total E1 strength is related to the root-mean-square radius of the neutron wave function in the ground state and shows corresponding scaling properties. We apply our approach to the E1 strength distribution of 11Be.

Study with RI beams at RIKEN and status of RIBF

Recent studies of shell structures of nuclei far from the stability line are presented. In particular studies with RI beams such as interaction cross sections, fragments momentum distributions reveal new dynamic change of shell structure. Special attention is paid on neutron halo nuclei in the p-sd shell. In halo nuclei and other neutron rich nuclei, the2s1/2 orbital shows irregular behavior. One such extreme case is the new neutron magic numberN=16. The global behavior of2s1/2 shell is discussed also in relation to the interaction cross-sections and fragment momentum distributions.

Study with RI beams at RIKEN and status of RIBF

Recent studies of shell structures of nuclei far from the stability line are presented. In particular studies with RI beams such as interaction cross sections, fragments momentum distributions reveal new dynamic change of shell structure. Special attention is paid on neutron halo nuclei in the p-sd shell. In halo nuclei and other neutron rich nuclei, the2s 1/2 orbital shows irregular behavior. One such extreme case is the new neutron magic number N=16. The global behavior of2s 1/2 shell is discussed also in relation to the interaction cross-sections and fragment momentum distributions.

Total Nuclear Reaction Cross Section Induced by Halo Nuclei and Stable Nuclei**The project supported by the State Key Basic Research Development Program of China under Contract No. G2000077400, the “100- Person Project” of the Chinese Academy of Sciences, National Natural Science Foundation of China under Grant Nos. 10175080, 10175082 10004012, and 19847002, and CAS Knowledge Innovation Project under Grant No.

We develop a method for calculation of the total reaction cross sections induced by the halo nuclei and stable nuclei. This approach is based on the Glauber theory, which is valid for nuclear reactions at high energies. It is extended for nuclear reactions at low energies and intermediate energies by including both the quantum correction and Coulomb correction under the assumption of the effective nuclear density distribution. The calculated results of the total reaction cross section induced by stable nuclei agree well with 30 experimental data within 10 percent accuracy.The comparison between the numerical results and 20 experimental data for the total nuclear reaction cross section induced by the neutron halo nuclei and the proton halo nuclei indicates a satisfactory agreement after considering the halo structure of these nuclei, which implies quite different mean fields for the nuclear reactions induced by halo nuclei and stable nuclei. The halo nucleon distributions and the root-mean-square radii of these nuclei can be extracted from the above comparison based on the improved Glauber model, which indicates clearly the halo structures of these nuclei. Especially, it is clear to see that the medium correction of the nucleon-nucleon collision has little effect on the total reaction cross sections induced by the halo nuclei due to the very weak binding and the very extended density distribution.

Medium energy antiproton absorption, a tool to study neutron halo nuclei

A novel method is proposed to measure the difference of neutron and proton density distributions of nuclei far off stability by medium energy antiproton absorption. The radioactive nuclei are produced by projectile fragmentation at medium energies (400–800) A MeV, separated and stored in a medium energy storage ring. The antiprotons are produced with 30 GeV protons, accumulated, cooled, decelerated and stored at energies of about 5 MeV in a small storage ring. The medium energy radioactive beams are brought to head on collisions with the low energy antiproton beam in an interaction section of both rings. The coasting radioactive beam and the reaction products from the collisions with the antiprotons are observed with the Schottky noise frequency analysis method, which allows one to separate all reaction products and measure their production rates as well as the loss rate of the primary beam. From these observations, the total and partial reaction cross sections may be determined, even with a small number of rare ion species in the ring. An analysis of the total and partial reaction cross sections will allow to determine both 〈 r p 2〉 as well as 〈 r n 2〉 for nuclei far off the stability.

Coulomb dissociation of halo nuclei

Coulomb dissociation of one neutron halo nuclei 11Be and 15,19C has been studied at energies around 70 A MeV by kinematically complete measurements of breakup particles at RIKEN. The experiment of 11Be breakup on a Pb target aims at studying the characteristic features of low-lying E1 strenght. In particular the effects of higher order excitation and nuclear contribution have been closely studied by using the impact parameter analysis. We have found that these contributions are very small, and the selection of the large impact parameter is useful to extract the spectroscopic information of the halo around state. We have then successfully applied this analysis method to 15C and 19C, where we have extracted the spectroscopic factor for the s-wave halo configuration. We also show preliminary results on the breakup of 11Be on a carbon target in order to study the nuclear breakup mechanism and low-lying discrete states of the halo nucleus.

Two-body and three-body halo nuclei

We have extracted the nuclear asymptotic normalization coefficients (ANC) for the virtual transitions B→A+N via some transfer reactions and the radioactive nuclear beam experiments. With these coefficients, root-mean-square (rms) radii for the valence particle in some possible halo nuclei have been calculated. The values of rms radii extracted with ANC approach are nearly model-independent, hence are a good quantity for the investigation of nuclear halo. In addition, we have also calculated the rms radii for the two valence neutrons in some three-body systems in terms of the relationship between the radii of valence particle, core nucleus and nuclear matter. With two conditions for nuclear halo formation, we have examined these extracted rms radii. The results show that11Be(1/2+, g.s),12B(1−, 2.621 MeV),13C(1/2+, 3.089 MeV),14C(0−, 6.903 MeV),14C(1−, 6.094 MeV),15C(1/2+, g.s) and19C(1/2+, g.s) with the valence particle in the 2s ground or excited state are the neutron halo nuclei, whereas17F(1/2+, 0.495 MeV) and21Na(1/2+, 2.423 MeV) are the proton halo nuclei in the excited state. For three-body systems, except the well-established two-neutron halo nuclei6He and11Li,14Be and17B might be the two-neutron halo nuclei as well.

Exact and approximate postform distorted-wave Born approximation amplitudes for the Coulomb breakup of neutron halo nuclei

The Coulomb breakup of neutron halo nuclei is considered within the framework of the postform distorted-wave Born approximation (DWBA). The quality of commonly used additional approximations to the DWBA theory is investigated by comparing the approximate with the exact DWBA calculations. The exact DWBA amplitude is expressed in momentum space as a three-dimensional integral and evaluated numerically. Calculations are presented for the Coulomb breakup of deuteron and ${}^{11}\mathrm{Be}$ at very forward angles at the beam energy of $\ensuremath{\sim}70 \mathrm{MeV}/\mathrm{nucleon}.$ The factorization approximation to the DWBA amplitude is studied and found to be suspected.

Halo Structure of Isobaric Analogue States in A = 21 and 17 Mirror Nuclei

The root-mean-square (rms) radii of the last nucleons in the2s1/2 states of 21Ne, 21Na, 17O and 17F arefound to be 4.4±0.5, 5.2±0.6, 4.3±0.5 and5.0±0.6 fm, respectively, from transfer reaction data. Theresults show that the 2s1/2 states of 21Na and 17F areproton halo states, while the analogous states in their mirror nuclei21Ne and 17O can be considered as neutron skin states.Comparisons among the rms radii of these states lead us to expectthat a neutron halo nucleus has a proton halo mirror partner, and theCoulomb barrier is a determinant factor limiting the extension of therms radius of the loosely bound proton.

Postacceleration effects in the Coulomb dissociation of neutron halo nuclei

We study the breakup of one-neutron halo nuclei in the Coulomb field of a target nucleus. In the post-form distorted wave Born approximation theory of this reaction, with only Coulomb distortions in the entrance and outgoing channels, an analytic solution for the breakup T matrix is known. We study this T matrix and the corresponding cross sections numerically. This formula can be related to the first order semiclassical treatment of the electromagnetic dissociation. This theory contains the electromagnetic interaction between the core and the target nucleus to all orders. We show that higher order effects (including postacceleration) are small in the case of higher beam energies and forward scattering. We investigate the beam energy dependence of the postacceleration effects. They are found to be quite important for smaller beam energies (slow collisions), but almost negligible at larger ones.

Beyond the Core+n+nModel Based on the Complex Scaling Method

With a new framework beyond the simple core+n+n model, we study neutron halo nuclei, taking into account a dynamical coupling between configurations of the core cluster and valence neutrons. It is shown that such a dynamical coupling is very important in 1 0 Li and 1 1 Li though less important in 6 He. We apply the new core+neutrons model to 9 Li+n and 9 Li+n+n where the 9 Li core includes J ϖ = 0 + neutron pairing correlations. In this new model, we solve the coupled channel OCM equation, and discuss the energy degeneracy of sand p-wave neutron orbits in 1 0 Li and the halo structure in 1 1 Li. In those calculations, the complex scaling method is extensively used to solve two-body and three-body resonances together with bound states in the same framework. The complex scaling method is also applied to the three-body Coulomb breakup by means of the extended completeness relation. This method is applied to the breakup reactions of 6 He and 1 1 Li.

Investigation of halo structure of 6He by hyperspherical three-body method

Hyperspherical harmonics expansion method is applied to a three-body model of two neutron halo nuclei. Convergence of the expansion has been ensured. A repulsive part is introduced in the interaction between the core and the extra-core neutron, to simulate Pauli principle. Two neutron separation energy, r.m.s. radii, correlation factor and probability density distributions have been calculated for 6He. It is found that the convergence of the two neutron separation energy is relatively slow, while other quantities reach convergence quickly.

α-clusterstructure in Be isotopes

The Be chain of isotopes is investigated within the semimicroscopicalgebraic cluster model (SACM). For that the SACM is applied to odd-massp-shell nuclei. We show that the main features of the Be isotopes can bewell explained. Though for the neutron halo nucleus 11Be someproblems remain, the shell model still can roughly describe the structuresof halo nuclei. In 11Be a shell inversion takes place as a result of thehigh deformation of the system. The quadrupole-quadrupole interaction isfound to play a dominant role in the structure of p-shell nuclei.

Multistep Coulomb and nuclear breakup of one-nucleon halo nuclei

Coulomb dissociation of one neutron halo nuclei ‘IBe and 15,1QC has been studied at energies around 70A MeV by kinematically complete measurements of breakup particles at RIKEN. The experiment of l1Be breakup on a Pb target aims at studying the characteristic features of low-lying El strength. In particular the effects of higher order excitation and nuclear contribution have been closely studies by using the impact parameter analysis. We have found that these contributions are very small, and the selection of the large impact parameter is useful to extract the spectroscopic information of the halo ground state. We have then successfully applied this analysis method to l”C and “C, where we have extracted the spectroscopic factor for the s-wave halo configuration. We also show preliminary results on the breakup of “Be on a carbon target in order to study the nuclear breakup mechanism and low-lying discrete states of the halo nucleus.

Higher order effects in electromagnetic dissociation of neutron halo nuclei

We investigate higher order effects in electromagnetic dissociation of neutron halo nuclei using a simple and realistic zero range model for the neutron-core interaction. In the sudden (or Glauber) approximation all orders in the target-core interaction are taken into account. Small deviations from the sudden approximation are readily calculated. We obtain very simple analytical results for the next-to-leading order effects, which have a simple physical interpretation. For intermediate energy electromagnetic dissociation, higher order effects are generally small. We apply our model to Coulomb dissociation of $^{19}$C at 67 A MeV. The analytical results are compared to numerical results from the integration of the time-dependent Schroedinger equation. Good agreement is obtained. We conclude that higher order electromagnetic effects are well under control.

Skyrme–Hartree–Fock Calculation on Exotic Light Nuclei**The project supported by the Major State Basic Research Development Program under Contract No. G2000774

The ground state properties of light nuclei are investigated by the Skyrme–Hartree–Fock approach with three sets of new force parameters SKI2, SKI3 and SKI4 [P.G. Reinhard and H. Flocard, Nucl. Phys. A 584 (1995) 467]. Calculations show that the Skyrme–Hartree–Fock theory with above force parameters provides a good description on the light isotopes except for some neutron-halo nuclei , and . Among the three sets of force parameters, SKI4, which has taken into consideration of the isospin dependence of the spin-orbit force, is the best one. Detailed comparison and analysis on the results are given.

Electromagnetic dissociation as a tool for nuclear structure and astrophysics

Coulomb dissociation is an especially simple and important reaction mechanism. Since the perturbation due to the electric field of the nucleus is exactly known, firm conclusions can be drawn from such measurements. Electromagnetic matrixelements and astrophysical S-factors for radiative capture processes can be extracted from experiments. We describe the basic theory, new results concerning higher order effects in the dissociation of neutron halo nuclei, and briefly review the experimental results obtained up to now. Some new applications of Coulomb dissociation for nuclear astrophysics and nuclear structure physics are discussed.