Proton Halo Structure Research Articles

Reaction dynamics of proton drip-line nuclei at energies around the Coulomb barrier

This work briefly introduces our recent studies on reactions induced by proton drip-line nuclei, 8B and 17F, at energies around the Coulomb barrier. Using detector arrays with large solid-angle coverage, the complete kinematics measurements were performed for systems of 8B+120Sn and 17F+58Ni. For the 8B+120Sn, the coincident measurement of the breakup fragments was achieved for the first time for a proton-halo nuclear system. The correlations between the breakup fragments reveal that the prompt breakup occurring on the outgoing trajectory dominates the breakup dynamics of 8B. For 17F+58Ni, the complete reaction channel information, such as quasi-elastic scattering, breakup and total fusion, was derived for the first time. An enhancement of the fusion cross section of 17F+58Ni was observed at the energy below the Coulomb barrier. Theoretical calculations indicate that this phenomenon is mainly due to the couplings to the continuum states. Moreover, different direct reaction dynamics were found in 8B and 17F systems, suggesting the influence of proton-halo structure on the reaction dynamics.

Theoretical Study of Proton Halo Structure and Elastic Electron Scattering Form Factor for 23Al and 27P Nuclei by Using Full Correlation Functions (Tensor Force and Short Range)

The study of proton-rich nuclei's form factors, root-mean-square radius (rms), and nuclear density distributions is the focus of this work for nuclei (23Al and 27P), use two body charge density distributions (2BCDD's). With the effects of the strong tensor force and short range, the nucleon distribution function of the two oscillating harmonic particles in a two-frequency shell model operates with two different parameters: bc for the inner (core) orbits and bv for the outer (halo) orbitals. This work demonstrated the existence of proton halo nuclei for the nuclei (23Al and 27P) in the shell (2s1/2), and the computed proton, neutron, and matter density distributions for these nuclei both displayed the long tail of the 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 dependent on the difference in the proton density distribution of the last proton in the nucleus. The Fortran 95 power station program was used to calculate the neutrons, protons, matter density, elastic electron scattering form factor, and rms radii. The calculated outcomes for these exotic nuclei agree well with the experimental data.

β-Delayed γ Emissions of 26P and Its Mirror Asymmetry

The study of the origin of asymmetries in mirror β decay is extremely important to understand the fundamental nuclear force and the nuclear structure. The experiment was performed at the National Laboratory of Heavy Ion Research Facility in Lanzhou (HIRFL) to measure the β-delayed γ rays of 26P by silicon array and Clover-type high-purity Germanium (HPGe) detectors. Combining with results from the β decay of 26P and its mirror nucleus 26Na, the mirror asymmetry parameter δ ( ≡ft+/ft−− 1) was determined to be 46(13)% for the transition feeding the first excited state in the daughter nucleus. Our independent results support the conclusion that the large mirror asymmetry is close to the proton halo structure in 26P.

Study of the proton halo structure of nuclei 23Al and 27P using the binary cluster model

The neutron, proton, and matter densities of the ground state of the proton-rich 23Al and 27P exotic nuclei were analyzed using the binary cluster model (BCM). Two density parameterizations were used in BCM calculations namely; Gaussian (GS) and harmonic oscillator (HO) parameterizations. According to the calculated results, it found that the BCM gives a good description of the nuclear structure for above proton-rich exotic nuclei. The elastic form factors of the unstable 23Al and 27P exotic nuclei and those of their stable isotopes 27Al and 31P are studied by the plane-wave Born approximation. The main difference between the elastic form factors of unstable nuclei and their stable isotopes is caused by the variation in the proton density distributions, especially the details of the outer part. Moreover, the Glauber model is used to calculate the matter rms radii and reaction cross-section of these exotic nuclei. The calculated results of the mentioned nuclei give a good accordance with the experimental data.

Possible neutron and proton halo structure in the isobaric analog states of A=12 nuclei

The differential cross sections of the $^{11}\mathrm{B}(^{3}\mathrm{He},d)^{12}\mathrm{C}$ reaction leading to formation of the ${0}^{+}$ ground state and the 15.11-MeV 1 ${}^{+}$, 16.57-MeV ${2}^{\ensuremath{-}}$, and 17.23-MeV ${1}^{\ensuremath{-}}$ excited states of $^{12}\mathrm{C}$ are measured at ${E}_{\text{lab}}=25$ MeV. The analysis of the data is carried out within the coupled-reaction-channels method for the direct proton transfer to the bound and unbound states. The rms radii of the last proton in all states studied are determined. A comparison of the rms radii of the $^{12}\mathrm{B}, ^{12}\mathrm{C}$, and $^{12}\mathrm{N}$ nuclei in the isobaric analog states (IASs) with isospin $T=1$ determined by different methods allows us to arrive at a conclusion that these nuclei in the ${1}^{\ensuremath{-}}$ excited states at ${E}_{x}=2.62, 17.23,$ and $1.80$ MeV, respectively, possess one-nucleon (neutron or proton) halo structure. The enlarged radii and a large probability of the last neutron to be outside of the range of the interaction potential are also found for the ${2}^{\ensuremath{-}}$ states of $^{12}\mathrm{B}, ^{12}\mathrm{C}$, and $^{12}\mathrm{N}$ at ${E}_{x}=1.67, 16.57,$ and $1.19$ MeV, respectively. These IASs also can be regarded as candidates for states with one-nucleon (neutron or proton) halo.

Large Isospin Asymmetry in Si22/O22 Mirror Gamow-Teller Transitions Reveals the Halo Structure of Al22

β-delayed one-proton emissions of Si22, the lightest nucleus with an isospin projection Tz=−3, are studied with a silicon array surrounded by high-purity germanium detectors. Properties of β-decay branches and the reduced transition probabilities for the transitions to the low-lying states of Al22 are determined. Compared to the mirror β decay of O22, the largest value of mirror asymmetry in low-lying states by far, with δ=209(96), is found in the transition to the first 1+ excited state. Shell-model calculation with isospin-nonconserving forces, including the T=1, J=2, 3 interaction related to the s1/2 orbit that introduces explicitly the isospin-symmetry breaking force and describes the loosely bound nature of the wave functions of the s1/2 orbit, can reproduce the observed data well and consistently explain the observation that a large δ value occurs for the first but not for the second 1+ excited state of Al22. Our results, while supporting the proton-halo structure in Al22, might provide another means to identify halo nuclei.Received 27 February 2020Revised 26 July 2020Accepted 14 September 2020DOI:https://doi.org/10.1103/PhysRevLett.125.192503© 2020 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasBeta decayNuclear structure & decaysProton emissionNuclear Physics

Nuclear-matter distribution in the proton-rich nuclei 7Be and 8B from intermediate energy proton elastic scattering in inverse kinematics

Absolute differential cross sections for elastic p7Be and p8B small-angle scattering were measured in inverse kinematics at an energy of 0.7 GeV/u at GSI Darmstadt. The hydrogen-filled ionization chamber IKAR was used as an active target to detect the recoil protons. The projectile tracking and isotope identification were performed with multi-wire proportional chambers and scintillation detectors. The measured cross sections were analysed using the Glauber multiple-scattering theory. The root-mean-square (rms) nuclear matter radii Rm=2.42(4) fm for 7Be and Rm=2.58(6) fm for 8B were obtained. The radial density distribution deduced for 8B exhibits a proton halo structure with the rms halo radius Rh=4.24(25) fm. A comparison of the deduced experimental radii is displayed with existing experimental and theoretical data.

Large mirror asymmetry in Gamow-Teller β-decay in the A = 26 isobaric multiplet

We investigate a striking example of mirror asymmetry in Gamow-Teller (GT) β-decay using the nuclear shell-model including isospin-nonconserving (INC) forces in the sd-shell region. We show that the large mirror asymmetry between 26P and 26Na GT β-decay can be accurately reproduced by introducing T=1, J≠0 INC forces related to the s1/2 orbit, while the usual J=0 INC force, commonly adopted to describe isospin-symmetry breaking, does not work. We further show that the calculated distribution of summed GT strength for the 26P β-decay is in good agreement with the experimental data. Our results support the conclusion that 26P is a nucleus with proton-halo structure.

Evidence of a Proton Halo in 23Al: A Mean Field Analysis

We have studied the nuclear structure properties like binding energy, charge radius, quadrupole deformation parameter for various isotopes of Al from the valley of stability to drip line region using the well known relativistic mean field formalism (RMF) with NL3 parameter set. We have compared our results with experimental data and found reasonable agreement. Further, we have taken spherical and deformed RMF densities to estimate the reaction dynamics of $^{23-28}$Al isotopes as projectiles and $^{12}$C as target by conjunction in Glauber model. The estimated results are also compared with the experimental data. The analysis of angular elastic differential and one proton removal cross sections are also studied with Glauber model many body system to investigate the structural feature of $^{23}$Al. The evidence of enhanced total reaction cross section, higher value of rms radius, narrow longitudinal momentum distribution and small proton separation energy of $^{23}$Al support its proton halo structure.

ASYMPTOTIC NORMALIZATION COEFFICIENTS FOR 7Be(p, γ)8B FROM RMF CALCULATION

The asymptotic normalization coefficient (ANC) method is used to determine the cross sections of peripheral reactions at astrophysical energies because of existence of the Coulomb barriers. In this paper, we address an estimation of the ANC of 8 B with its single particle wavefunction obtained within the framework of relativistic mean field (RMF) theory. We test the force parameters used in the RMF theory by comparing the calculated structure properties of A = 7–9 drip-line nuclei with experimental results. Utilizing the corrected bound wavefunction of 8 B , the ANC [Formula: see text] is obtained and that indicates the S17(0) is 18.07 eV b. Additionally, we find that the root-mean-square (rms) radius for the loosely bound proton in 8 B is 3.98 fm. This confirms that 8 B has a proton halo structure.

Description of N = 7 ∼ 9 Isotones with a Modified Single-Particle Potential

We study the level structures of N = 7 ∼ 9 isotones and their mirror nuclei in the framework of the single-particle potential model. Considering the limitation of the conventional potential-model calculation, the isospin-dependent l2 coupling is newly introduced in the average potential. The modified model gives a unified description for the structures of all studied nuclei. Calculations self-consistently produce the s-d level inversion in N = 9 isotones and their mirror nuclei. Meanwhile, the s-p level inversion in the mirror nuclei 11Be and 11N is reproduced. The study confirms the neutron halo structures in 11Be(2s1/2), 11Be(1p1/2), 12B(2s1/2), 14B(2s1/2), 13C(2s1/2), 15C(2s1/2) and the proton halo structure in 17F(2s1/2). The agreement between theory and experiment indicates that the inclusion of the l2 coupling is a feasible way to explain the abnormal structures of exotic light nuclei.

Quadrupole moment and a proton halo structure in 17F (Iπ = 5/2+)

The quadrupole moment of light nuclei 17F in the ground state (Iπ = 5/2+) is measured by the β–NMR method. The effective charge of the last proton in a d5/2 orbit for 17F is extracted from the measured quadrupole moment Q(17F) divided by the quadrupole moment Qsp calculated with a single particle model. A proton effective charge of eeffp = 1.12 ± 0.07e is obtained, which is in agreement with that given by a particle–vibration coupling model calculation within the experimental error. The present value of the proton effective charge is strong evidence for the existence of a proton skin in 17F (Iπ = 5/2+).

Asymptotic Normalization Coefficient of 27P →26Si + p and Radius of 27P Halo

The asymptotic normalization coefficient of the virtualdecay 27P → 26Si + p is extracted to be1840±240 fm−1 from the peripheral26Mg(d,p)27Mg reaction using charge symmetry of mirrorpair, for the first time. It is then used to derive therms radius of the valence proton in the ground state of 27P. Weobtain the rms radius ⟨r2⟩1/2 = 4.57±0.36 fm,significantly larger than the matter radius of 27P. The probabilityof the valence proton outside the matter radius of 27P is found tobe 73%. The present work supports the conclusion that the 27P groundstate has a proton halo structure.

Nuclear Radii Extracted from Experimental Reaction CrossSections

We illustrate typical experimental reaction cross sections σRwhich have obtained on RIBLL at Heavy Ion Research Facility of theInstitute of Modern Physics (IMP) at Lanzhou. The corresponding nuclearradii are extracted from the measured experimental σR usingthe Glauber model. Meanwhile, theoretical nuclear radii are alsocalculated using Relativistic density-dependent Hartree and sphericalrelativistic mean-field theory with Pauli blocking. For comparison, thenuclear radii of these nuclei are also calculated using the empiricalradius format in which the deformation has been taken into account. Fromthe given experimental and theoretical nuclear radii, we suggest thatthere may exist proton halo structure in 23Al, 27P and may existproton skin structure in 24Al. We also find that thedeformation plays a great role to the nuclear radii.

POSSIBLE EXOTIC STRUCTURE IN LIGHT PROTON-RICH NUCLEI

Radioactive ion beams were produced through the projectile fragmentation induced by 69MeV/nucleon 36 Ar primary beam on a 9 Be target. Measurements of reaction cross section (σR) for some proton-rich nuclei on carbon target at intermediate energies around 30MeV/nucleon have been performed on RIBLL of HIRFL by transmission method and transmission plus transportation method. The experimental σR values for 23Al and 27P are abnormally large compared with their neighboring nuclei and that of 17F has an enhancement compared with the neighboring isotopes. It suggests anomalously large matter root-mean-square radii and proton halo structure in 23 Al and 27 P . The experimental σR values and momentum distribution of fragmentation reaction product for 31 Cl , 32 Cl , 33 Cl , 28 S , 29 S were performed also on RIBLL by transmission and transportation method. These data are in analyzing. The calculation of relativistic density-dependent Hartree shows that the nuclei 23 Al , 27 P , 31 Cl may have proton-halo structure and 17F, 32Cl may have proton-skin structure. New experiment on the search for new nuclides 25 P and 26 S in proton drip line is also described. The significance of these measurements and possible proton halo and skin for light proton-rich nuclei has been discussed.

Reactions of Proton Halo Nuclei in a Relativistic Optical Potential

The reaction cross section, σR, of the proton halo nuclei 17Ne and 12N on Si is calculated using an optical potential derived from the solution of the Dirac–Brueckner–Bethe–Goldstone equation, starting from the one-boson-exchange-potential of Bonn. The nuclear densities are generated from self-consistent Hartree–Fock calculations using the recent Skyrme interaction SKRA. It is found that the enhancement in the reaction cross section found experimentally for the 17Ne + Si system in comparison to 15O + Si, where 15O has been considered as a core of 17Ne, is mainly due to the proton halo structure of 17Ne which increases the interaction, in the surface and tail regions. Glauber model calculations did not produce this enhancement in σR for proton halo nuclei.

Measurement of reaction cross section for proton-rich nuclei ( A

Radioactive ion beams were produced through the projectile fragmentation induced by 69 MeV/ nucleon 36Ar primary beam on a 9Be target. Measurements of reaction cross sections ( σ R 's) for 44 nuclei with A<30 (mostly proton-rich), on carbon were performed on RIBLL (Radioactive Ion Beam Line in Lanzhou) of HIRFL (Heavy Ion Research Facility in Lanzhou) at intermediate energies around 30 MeV/nucleon by a transmission method. The experimental σ R values for 23Al and 27P are abnormally large compared with their neighboring nuclei. Together with the previous experimental facts such as the binding energy and ground state data, it suggests anomalously large matter root-mean-square radii and proton halo structure in 23Al and in 27P. There is an enhancement for the σ R of 17F + 12C compared with the neighboring isotopes. Considering that the ground state of 17F is 1 d 5/2, this can indicate that there is a proton skin in 17F. The calculation of relativistic density-dependent Hartree model (RDDH) shows that the nuclei 23Al and 27P may have proton-halo structure and 17F may have proton-skin structure. The significance of these measurements is discussed.

First observation of neutron–proton halo structure for the 3.563 MeV 0+ state in 6Li via 1H(6He, 6Li)n reaction

The angular distributions of the charge exchange reaction 1 H( 6 He, 6 Li) n were measured in reverse kinematics with a secondary 6 He beam at the energy of 4.17 A MeV. The data were analyzed in the context of a microscopic calculation. It is shown that both the ground state of 6 He and the second excited state of 6 Li (3.563 MeV, 0 + ) have halo structure.

Possible Proton Halo and Skin in Light Proton-Rich Nucleus

Measurements of reaction cross section (sigma(R)) for some proton-rich nuclei (N = 8, 10, 12 isotones) on carbon target at intermediate energies have been performed on RIBLL of HIRFL by a transmission method. The experimental sigma(R) values for Al-23 and P-27 are abnormally large compared with its neighboring nuclei and that of F-17 has an enhancement compared with neighboring isotopes. The calculation of relativistic density-dependent Hartree (RDDH) approach shows there is proton-halo structure in Al-23 and P-27 and there is a proton-skin in F-17. The significance of these measurements was discussed.

Nuclear electromagnetic moments. [formula omitted]-NMR and its applications

Studies of magnetic moments and electric quadrupole moments for light unstable nuclei, which have been opened up by the recent development of spin-polarized radioactive nuclear beams and the β-ray detected nuclear magnetic resonance technique, are reviewed. The results lead to several intriguing findings concerning structures and interactions in unstable nuclei far from the stability line, such as a proton-halo structure in proton-rich nuclei, displacement of the single particle levels and quenching of the neutron effective charge in neutron-rich nuclei, and an anomalously large spin expectation value in a T=3/2 mirror pair. Applications of the present techniques to the study of hyperfine interactions of radioactive atoms introduced in solids are also discussed.