6He Nucleus Research Articles

Sizes of the Neutron–Proton Halo in Nucleon-Stable States of the 6Li Nucleus

The matter, neutron, and proton radii of nucleon-stable 1+ and 0+ states of the 6Li nucleus are studied theoretically within the no-core shell model. The results have been comparatively analyzed with the radii of the 0+ state of the 6He nucleus. To increase the accuracy of calculations, we have developed an extrapolation procedure. A new definition of the quantitative measure has been proposed and justified to describe the properties of a halo formed by loosely bound neutrons and protons in the A-nucleon problem. The sizes of the halo in the indicated states of 6Li have been calculated for the first time. It has been demonstrated that the sizes of their halos are close to those of the two-neutron halo in 6He. Thus, additional reliable evidence of the existence of the neutron–proton halo in the discussed states of 6Li has been obtained.

PROPERTIES OF LIGHT NUCLEI 6He AND 6Be IN THE FRAMEWORK OF THE THREE-CLUSTER MODEL

This scientific work is the study of the structure of light nuclei 6He and 6Be in the framework of the three-cluster α+2n-model. The calculation methods have been based on the variational solution of the stationary Schrödinger equation for the relative motion of three clusters in 6He and 6Be nuclei, respectively. The realistic Reid potential has been chosen as the nucleon-nucleon interaction potential, and the potential with even-odd wave splitting has been used for the interaction of the alpha-particle and nucleons. Realistic wave functions of the relative motion of the alpha particle and nucleons in these nuclei and low-lying energy levels have been calculated. The static observables of the 0+ ground state of 6He and 6Be nuclei, in particular, the root-mean-square charge and material radii and binding energies, have been determined. The obtained values of the root-mean-square charge and material radii of the 6He nucleus confirm the hypothesis of the presence of a neutron halo structure of this nucleus.

Microscopic spin-orbit potential for p +6He elastic scattering

In this work, we simultaneously reanalyzed the differential elastic scattering cross-sections ([Formula: see text]) and the vector analyzing power ([Formula: see text]) of [Formula: see text]He elastic scattering. This analysis was performed using the folded optical model for both real central and spin-orbit (SO) potentials, respectively. For the imaginary central, we used the usual Woods-Saxon (WS) form. Three different model density distributions are used to calculate the potential. We aimed to examine the applicability of the microscopically derived SO potential and the structure effect of 6He nucleus. The presence of the [Formula: see text] experimental data of [Formula: see text]He makes it interesting for this study. Our calculations showed that the three densities gave similar predictions for the cross-sections data. The three microscopic SO potentials calculations of [Formula: see text] are not in a good agreement with the experimental data. We concluded that the SO formalism in its current form needs more investigations for exotic halo nuclei.

Proton elastic scattering at 200 A MeV and high momentum transfers of 1.7–2.7 fm−1 as a probe of the nuclear matter density of 6He

Differential cross sections of p–6He elastic scattering were measured in inverse kinematics at an incident energy of 200 A MeV, covering the high momentum transfer region of 1.7–2.7 fm−1. The sensitivity of the elastic scattering at low and high momentum transfers to the density distribution was investigated quantitatively using relativistic impulse approximation calculations. In the high momentum transfer region, where the present data were taken, the differential cross section has an order of magnitude higher sensitivity to the inner part of the 6He density relative to the peripheral part (15:1). This feature makes the obtained data valuable for the deduction of the inner part of the 6He density. The data were compared to a set of calculations assuming different proton and neutron density profiles of 6He. The data are well reproduced by the calculation assuming almost the same profiles of proton and neutron densities around the center of 6He, and a proton profile reproducing the known point-proton radius of 1.94 fm. This finding is consistent with the assumption that the 6He nucleus consists of a rigid α-like core with a two-neutron halo.

Possible Existence of Neutron-Proton Halo in 6Li

One of the most recent results was the determination of the proton halo in the first excited state of the 13N nucleus using of an analog of the MDM method for the charge exchange reactions (3He, t). It turned out that this state has the same radius as the mirror state 1/2+, 3.09 MeV in 13C.This observation allows us to take the next step and try to apply this approach to measure the radii of states. The increased radii in the isobar - analogue states of the 6He-6Li-6Be triplet, which may also have a halo structure, are not excluded. As a first step, we analyzed the published differential cross sections for inelastic scattering of 3He + 6Li with the excitation of the 2.19 MeV, 3+ state at energies 34 and 72 MeV and 3.56 MeV, 0+ state at energies 24.6 and 27 MeV. Probably the state 0+, 3.56 MeV has the same radius as its ”Borromian” isobar analogue 6He and is neutron-proton halo. The predicted enlarged radius because of the more extended wave function p - n, apparently, does not take place. We recall that the spatial structure of the 6He nucleus was predicted to be quite complex, in which correlations of two types appeared: ”cigar” and ”dineutron”. The question arises: does the structure of the state change so much when passing from 6He to the isobar-analoguein6Li,whichrequirestheintroductionofaspecialkindof“tango-halo”.

Folding model calculations for 6He+12C elastic scattering

In the framework of the double folding model, we used the α+2n and di-triton configurations for the nuclear matter density of the 6He nucleus to generate the real part of the optical potential for the system 6He+12C. As an alternative, we also use the high energy approximation to generate the optical potential for the same system. The derived potentials are employed to analyze the elastic scattering differential cross section at energies of 38.3, 41.6 and 82.3 MeV/u. For the imaginary part of the potential we adopt the squared Woods-Saxon form. The obtained results are compared with the corresponding measured data as well as with available results in the literature. The calculated total reaction cross sections are investigated and compared with the optical limit Glauber model description.

Atomic electron distribution and recoil effects following beta decay of the halo nucleus helium-6

SynopsisFollowing the β decay of a 6He nucleus to form 6Li, the atomic electrons adjust to the sudden change of nuclear charge from 2 to 3. The probabilities for electron shake-up and shake-off are calculated, including recoil effects, by the use of a Stieltjes imaging representation of the final states. The results will be applied to ongoing angular correlation studies in a search for new physics beyond the Standard Model.

A theoretical analysis of the 6He + 9Be reaction: phenomenological and double folding model approximations

We investigate the elastic scattering data of the 6He + 9Be reaction by using the phenomenological and double folding model potentials within the framework of the optical model. In the phenomenological calculations, we use the optical model parameters existed in literature to explain 6He + 9Be reaction. The real potentials in double folding calculations are obtained by using two different density distributions of 6He nucleus. For both the phenomenological and double folding model calculations, the imaginary potentials have the shape of the Woods-Saxon volume. We compare the phenomenological model results with the double folding model ones as well as the experimental data. We present that the folding model results are in better agreement with the experimental data than the phenomenological results for the 6He + 9Be reaction.

Optical model description of the elastic scattering of 6He from a polarized proton target at 71 MeV/nucleon

The vector analyzing power and differential cross section for the elastic scattering of 6He nucleus from polarized protons at 71 MeV/nucleon have been analyzed using the optical model potentials. Different versions of the nuclear potential are constructed using phenomenological potentials and semimicroscopic potentials based upon four different versions of 6He density and three effective nucleon-nucleon interactions. The effects of density dependence and the sensitivity of the cross sections for interactions have been investigated.

AN INVESTIGATION OF 6HE+12C ELASTIC SCATTERING USING MICROSCOPIC CLUSTER MODEL

In the frame work of the cluster folding model, for the first time, the 6He+12C real folded potentials are derived using newforms of the nuclear matter density of 6He nucleus based on α+2n or di-triton configurations. The angular distributions ofthe elastic scattering differential cross section at energies 38.3,41.6 and 82.3 MeV/nucleon are reexamined using the generatedpotentials. Comparisons between the extracted and measured angular distributions of the differential cross sections arepresented. Satisfactory reproduction of the data is extracted by using the square Woods-Saxon (WS2) form instead of the usualWS shape without need to renormalize the derived potentials. The resulted reaction cross sections are also investigated andcompared with the optical limit Glauber model predictions.

Optical model analysis of p+6He scattering over a wide range of energy

Optical-model analysis of proton elastic scattering from 6He has been carried out for eight sets of elastic scattering data at energies, 24.5, 25.0, 36.2, 38.3, 40.9, 41.6, 71.0 and 82.3 MeV/n respectively. The vector analyzing power and differential cross section for the elastic scattering of 6He nucleus from polarized protons at 71 MeV have been analyzed in the framework of the optical model potentials. The data are, first, analyzed in term of phenomenological potentials using the Woods-Saxon form for the real and imaginary parts supplemented by a spin-orbit potential of Thomas form. The analysis has been also performed using microscopic complex potentials.

A cluster calculation for 6He spectrum

The 6He nucleus is considered as the cluster α + n + n system. The excitation energies of the low-lying levels are calculated using the configuration-space Faddeev equations. The analytical continuation method in a coupling constant is applied for calculation of resonance parameters. The αn interaction is constructed to reproduce the results of R-matrix analysis for αn-scattering data. A realistic AV14 potential describes the nn interaction. Additional three-body potential adjusted by the ground state energy of 6He is used. The energies of the low-lying resonances of 6He (01+, 02+, 21+) are reasonably reproduced by the calculations.

Microscopic description of translationally invariant core+N+Noverlap functions

We derive expressions for core + N + N overlap integrals starting from microscopic wave functions obtained in the ab initio no-core shell model. These overlap integrals correspond to three-body channel form factors and can be used to investigate the clustering of many-body systems into a core plus two nucleons. We consider the case when the composite system and the core are described in Slater determinant, harmonic oscillator bases, and we show how to remove spurious center of mass components exactly in order to derive translationally-invariant overlap integrals. We study in particular the Borromean 6He nucleus using realistic chiral nuclear interactions, and we demonstrate that the observed clusterization in this system is a Pauli focusing effect. The inclusion of three-body forces has a small effect on this structure. In addition, we discuss the issue of absolute normalization for spectroscopic factors, which we show is larger than one. As part of this study we also perform extrapolations of ground-state observables and investigate the dependence of these results on the resolution scale of the interaction.

Analyzing Power in Elastic Scattering of Polarized Protons from Neutron-rich Helium Isotopes

The vector analyzing power has been measured for the elastic scattering of neutron-rich 6He from polarized protons at 71 MeV/nucleon. Two approaches based on local one-body potentials were applied to investigate the spin-orbit interaction between a proton and a 6He nucleus. An optical model analysis revealed that the spin-orbit potential for 6He is characterized by a shallow and long-ranged shape compared with the global systematics of stable nuclei. A semi-microscopic analysis with a α + n + n cluster folding model suggests that the inclusion of realistic interaction between a proton and the α core is important in describing the p-6He elastic scattering.

A theoretical study on 120Sn(6He, 6He)120Sn elastic scattering

In this study, we analyze 120Sn(6He,6He)120Sn elastic scattering with both the phenomenological (WS) and microscopic double folding (DF) potentials. In the phenomenological calculations we use the optical model (OM) parameters acquired from literature. DF potentials have been obtained for no-core shell model (NCSM) density distribution (DD) of 6He nucleus. The phenomenological results is compared with DF model results as well as the experimental data. These comparison provides information about the similarities and differences of the models used in calculations.

Study of the structure of light, unstable nuclei and the mechanism of elastic proton scattering

The review presents calculations of elastic p 6He-, p 8Li-, p 9Li- and p 9C scattering in the framework of the Glauber theory of multiple diffraction scattering at intermediate energies of 70 and 700 MeV/nucleon. The most significant result of the calculations is that we have utilized realistic three-body wave functions obtained within modern nuclear models. The relation is found between differential cross sections and intercluster potentials, where the nuclear wave functions are calculated. Conclusions are made concerning the types of potentials which describe most realistically the available experimental data. The method for calculation of three-body wave functions in α-n-n-, α-t-n-, 7Be-p-p-, α-t-2n-, and 7Li-n-n models is described with discussion of inter-cluster potentials and the quantum-number configurations taken into consideration. It is revealed how the wave functions and the nuclear electromagnetic characteristics calculated using these wave functions depend on the choice of intercluster potentials. The derivation of matrix elements (amplitudes) of pA scattering in the framework of the Glauber approach with three-body wave functions is presented by an example of 6He nucleus. Discussing the results of calculation of differential cross sections and the analyzing power (A y ), we established how the calculated characteristics depend on a wave-function structure and dynamics of the process determined by a Glauber operator of multiple scattering. The calculated differential cross sections and analyzing powers are compared with available experimental data and calculations by other authors performed for different formalisms, which allows us to make justified conclusions.

Analyzing power in elastic scattering of6He from a polarized proton target at 71 MeV/nucleon

The vector analyzing power has been measured for the elastic scattering of neutron-rich 6He from polarized protons at 71 MeV/nucleon making use of a newly constructed solid polarized proton target operated in a low magnetic field and at high temperature. Two approaches based on local one-body potentials were applied to investigate the spin-orbit interaction between a proton and a 6He nucleus. An optical model analysis revealed that the spin-orbit potential for 6He is characterized by a shallow and long-ranged shape compared with the global systematics of stable nuclei. A semimicroscopic analysis with a alpha+n+n cluster folding model suggests that the interaction between a proton and the alpha core is essentially important in describing the p+6He elastic scattering. The data are also compared with fully microscopic analyses using non-local optical potentials based on nucleon-nucleon g-matrices.

Halo effects on fusion cross section in 4,6He+64Zn collision around and below the coulomb barrier

The structure of the halo nuclei is expected to influence the fusion mechanism at energies around and below the Coulomb barrier. Here new data of 4He+64Zn at sub-barrier energies are presented which cover the same energy region of previous measurements of 6He+64Zn. The fusion cross section was measured by using an activation technique where the radioactive evaporation residues produced in the reaction were identified by the X-ray emission which follows their electron capture decay. By comparing the two system, we observe an enhancement on the fusion cross section in the reaction induced by 6He, at energy below the Coulomb barrier. It is shown that this enhancement seems to be due to static properties of halo 2n 6He nucleus.

Proton momentum distributions in the 7Li nucleus in a potential cluster model

Distributions of the proton momentum in the 7Li{αt} → p + 6He{αnp} fragmentation channel were, along with the corresponding widths and spectroscopic factors, calculated in the αnn model representation of wave functions of the 6He nucleus in the (0+,1) ground and (2+,1) excited states. The results are compared to the available theoretical calculations and experimental NIKHEF data on the 7Li(e,e′p)6He electron-induced proton knock-out process.

Quasifree proton scattering on halo nuclei as a tool for studying the neutron-halo structure

An experimental method is proposed for investigating the structure of the two-neutron halo in quasifree proton scattering on clusters of halo nuclei. This scattering process is studied in inverse kinematics by using a 6He beam incident to a stack of track emulsions. Preliminary data on the reaction 6He + p → 4He + p + X are compared with the results of simple kinematical calculations for quasifree proton scattering on the clusters forming the halo of the 6He nucleus.