Neutron Skin Research Articles

Neutron radii and neutron skin of neutron-rich nuclei deduced from proton-nucleus total reaction cross sections

A new method is proposed to deduce the neutron radii of neutron-rich nuclei. This method requires measuring the reaction cross sections of both the neutron-rich nucleus and its stable isotope at the same energy per nucleon on a proton target. Using this method and the available experimental data of 12,22C + p and 9,14Be + p at 40A MeV, the neutron radii of 22C and 14Be have been deduced.

Swelling of Doubly Magic ^{48}Ca Core in Ca Isotopes beyond N=28.

Interaction cross sections for ^{42-51}Ca on a carbon target at 280 MeV/nucleon have been measured for the first time. The neutron number dependence of derived root-mean-square matter radii shows a significant increase beyond the neutron magic number N=28. Furthermore, this enhancement of matter radii is much larger than that of the previously measured charge radii, indicating a novel growth in neutron skin thickness. A simple examination based on the Fermi-type distribution, and mean field calculations point out that this anomalous enhancement of the nuclear size beyond N=28 results from an enlargement of the core by a sudden increase in the surface diffuseness of the neutron density distribution, which implies the swelling of the bare ^{48}Ca core in Ca isotopes beyond N=28.

Constraints on the symmetry energy and its associated parameters from nuclei to neutron stars

The symmetry energy obtained with the effective Skyrme energy density functional is related to the values of isoscalar effective mass and isovector effective mass, which is also indirectly related to the incompressibility of symmetric nuclear matter. In this work, we analyze the values of symmetry energy and its related nuclear matter parameters in five-dimensional parameter space by describing the heavy ion collision data, such as isospin diffusion data at 35 MeV/u and 50 MeV/u, neutron skin of $^{208}\mathrm{Pb}$, and tidal deformability and maximum mass of neutron star. We obtain the parameter sets which can describe the isospin diffusion, neutron skin, tidal deformability, and maximum mass of neutron star, and give the incompressibility ${K}_{0}=250.23\ifmmode\pm\else\textpm\fi{}20.16$ MeV, symmetry energy coefficient ${S}_{0}=31.35\ifmmode\pm\else\textpm\fi{}2.08$ MeV, the slope of symmetry energy $L=59.57\ifmmode\pm\else\textpm\fi{}10.06$ MeV, isoscalar effective mass ${m}_{s}^{*}/m=0.75\ifmmode\pm\else\textpm\fi{}0.05$, and quantity related to effective mass splitting ${f}_{I}=0.005\ifmmode\pm\else\textpm\fi{}0.170$. At two times normal density, the symmetry energy we obtained is in 35--55 MeV. To reduce the large uncertainties of ${f}_{I}$, more critical works in heavy ion collisions at different beam energies are needed.

Study of the Nuclear Structure for 38Ar, 59Co, 124Sn, 146Nd, 153Eu and 203Tl Target Nuclei Used in Fabrication the Nuclear Batteries

The nuclear structure of 38Ar, 59Co, 124Sn, 146Nd, 153Eu and 203Tl target nuclei used in technology for nuclear batteries have been investigation, in order that, these nuclei are very interesting for radioisotope thermo-electric generator (RTG) space studies and for betavoltaic battery microelectronic systems. The single particle radial density distribution, the corresponding root mean square radii (rms), neutron skin thicknesses and binding energies have been investigated within the framework of Hartree-Fock Approximation with Skyrme interaction. The bremsstrahlung spectrums produced by absorption of beta particles in betavoltaic process and backscattered photons spectrum have also been calculated. All obtained results compared with available experimental data.

Chiral g -matrix folding-model approach to reaction cross sections for scattering of Ca isotopes on a C target

We first predict the ground-state properties of Ca isotopes, using the Gogny-D1S Hartree-Fock-Bogoliubov (GHFB) with and without the angular momentum projection (AMP). We find that $^{64}$Ca is an even-dripline nucleus and $^{59}$Ca is an odd-dripline nucleus, using $A$ dependence of the one-neutron separation energy $S_{1}$ and the two-neutron separation energy, $S_{2}$. As for $S_{1}$, $S_{2}$ and the binding energies $E_{\rm B}$, our results agree with the experimental data in $^{40-58}$Ca. As other ground-state properties of $^{40-60,62,64}$Ca, we predict charge, proton, neutron, matter radii, neutron skin and deformation. As for charge radii, our results are consistent with the experimental data in $^{40-52}$Ca. For $^{48}$Ca, our results on proton, neutron, matter radii agree with the experimental data. Very lately, Tanaka et. al. measured interaction cross sections for $^{42-51}$Ca scattering on a $^{12}$C target at an incident energy per nucleon of $E_{\rm lab}=280$MeV. Secondly, we predict reaction cross sections $\sigma_{\rm R}$ for $^{40-60,62,64}$Ca, using a chiral $g$-matrix double-folding model (DFM). To show the reliability of the present DFM for $\sigma_{\rm R}$, we apply the DFM for the data on $^{12}$C scattering on $^{9}$Be, $^{12}$C, $^{27}$Al targets in $30 < E_{\rm lab} < 400 $MeV, and show that the present DFM is good in $30 < E_{\rm lab} < 100 $MeV and $250 < E_{\rm lab} < 400 $MeV. For $110 < E_{\rm lab} < 240 $MeV, our results have small errors. To improve the present DFM for $\sigma_{\rm R}$, we propose two prescriptions.

Parametrization of the surface energy in the ETF approximation

We perform extended Thomas–Fermi calculations in the Wigner–Seitz cell below and above neutron drip with realistic functionals. The resulting energy density is decomposed as a sum of bulk terms and a surface term, and a compressible liquid drop analytical formula is used to fit the surface tension. The effect of curvature terms and neutron skin is studied in detail. A very good reproduction of the microscopic data is obtained using an expression that depends only on the mass and charge of the cluster, showing that the in-medium modifications of the nuclear energy in the presence of an external neutron gas can be effectively accounted for in the isospin dependence of the surface tension. In this first application, aimed at establishing the fitting protocol, we concentrate on the Sly4 energy functional, but the study can be easily generalized to different functionals, and the resulting parametrizations can be used for direct applications in pasta calculations in neutron star crusts and supernova matter.

A hybrid model of Skyrme- and Brueckner-type interactions for neutron star matter

Abstract We suggest a hybrid model for neutron star matter to discuss the hyperon puzzle inherent in the 2.0 M$_{\odot}$ of the neutron star. For the nucleon–nucleon ($NN$) interaction, we employ the Skyrme–Hartree–Fock approach based on various Skyrme interaction parameter sets, and take the Brueckner–Hartree–Fock approach for the interactions related to hyperons. For the many-body interactions including hyperons, we make use of the multi-pomeron-exchange model, whose parameters have been adjusted to the data deduced from various hypernuclei properties. For clear understanding of the physics in the hybrid model, we discuss fractional functions of related particles, symmetry energies, and chemical potentials in dense matter. Finally, we investigate the equations of state and mass–radius relation of neutron stars, and show that the hybrid model can properly describe the 2.0 M$_{\odot}$ neutron star mass data with the many-body interaction employed in the hybrid model. Recent tidal deformability data from the gravitational wave observation are also compared to our calculations, especially in terms of the neutron skin of $^{208}$Pb and nuclear incompressibility.

Coherent elastic neutrino-nucleus scattering on Ar40 from first principles

Coherent elastic neutrino scattering on the 40Ar nucleus is computed with coupled-cluster theory based on nuclear Hamiltonians inspired by effective field theories of quantum chromodynamics. Our approach is validated by calculating the charge form factor and comparing it to data from electron scattering. We make predictions for the weak form factor, the neutron radius, and the neutron skin, and estimate systematic uncertainties. The neutron-skin thickness of 40Ar40 is consistent with results from density functional theory. Precision measurements from coherent elastic neutrino-nucleus scattering could potentially be used to extract these observables and help to constrain nuclear models.

Nuclear Forces in the Medium: Insight From the Equation of State

In this review, we concentrate on recent efforts of our group aimed at investigating the nuclear equation of state of symmetric nuclear matter (equal concentrations of protons and neutrons) and the one of pure neutron matter. Although idealized, these systems are suitable \laboratories to probe nuclear forces in the many-body system. The energy per particle as a function of density can reveal rich information about the nature of nuclear forces in the medium and how they impact observable properties. For instance, the pressure in neutron-rich matter has been found to have profound impact on very diverse systems, ranging from the thickness of the neutron skin in a heavy nucleus to the properties of compact stars. The current trend in nuclear physics is to build few-nucleon forces according to the prescription of chiral effective field theory. We open by reviewing in depth how we develop equations of state based on state-of-the-art chiral interactions. We then highlight some applications in neutron-rich nuclei and neutron stars.

Collective excitations involving spin and isospin degrees of freedom

In this paper, we discuss some new important developments in the study of isobaric analog states (IAS) and Gamow-Teller resonances (GTR). In the case of the IAS, we have shown the importance of taking into account charge symmetry breaking (CSB) and charge independence breaking (CIB) forces, in order to reconcile the reproduction of the IAS energy in 208Pb with the reproduction of some very basic observables like the neutron skin which, in turn, is strongly correlated with the density dependence of the symmetry energy. Isospin symmetry breaking terms can increase the energy of the IAS associated with Skyrme EDFs that produce a reasonable value of the neutron skin. In particular, this has been shown in the case of the SAMi functional. The GTR has a large damping width and its strength is experimentally found to be quenched with respect to standard RPA calculations. We have revised the PVC model for the width of giant resonances using the Skyrme force consistently for RPA (QRPA) and (quasi-)particle-vibration couplings (PVC or QPVC) calculations. We apply this model to the study of the GTR both in magic and open-shell nuclei. The results are in very good agreement with the experimental findings. The remaining discrepancies point to the necessity of fine tuning of the spin, spin-isospin, and spin-orbit terms in the existing EDFs. Some detailed formulas of CSB and CIB energy densities are given in the appendix.

Pygmy resonances and symmetry energy

I present a brief summary of the first three decades of studies of pygmy resonances in nuclei and their relation to the symmetry energy of nuclear matter. I discuss the first experiments and theories dedicated to study the electromagnetic response in halo nuclei and how a low energy peak was initially identified as a candidate for the pygmy resonance. This is followed by the description of a collective state in medium heavy and heavy nuclei which was definitely identified as a pygmy resonance. The role of the slope parameter of the symmetry energy in determining the properties of neutron stars is stressed. The theoretical and experimental information collected on pygmy resonances, neutron skins, and the numerous correlations found with the slope parameter is briefly reviewed.

Electroweak probe of neutron skins of nuclei

We describe a program of elastic electron scattering experiments aimed at direct measurements of the neutral weak form factor of nuclei from which the neutron rms radii of nuclei can be extracted with little theoretical ambiguity. The difference between the neutron and proton rms radii, the neutron skin, is intimately related to the density dependence of the symmetry energy in dense nuclear matter which in turn can be related to neutron star parameters such as mass, radius and mass quadrupole polarizability.

Electroweak probes of ground state densities

Elastic electron scattering has been used to paint the most accurate picture of the proton distribution in atomic nuclei. Spurred by new experimental developments, it is now possible to gain valuable insights into the neutron distribution using exclusively electroweak probes. Our goal is to assess the information content and complementarity of the following three electroweak experiments in constraining the neutron distribution of atomic nuclei: (a) parity violating elastic electron scattering, (b) coherent elastic neutrino nucleus scattering, and (c) elastic electron scattering of unstable nuclei. Relativistic mean-field models informed by the properties of finite nuclei and neutron stars are used to compute ground state densities and form factors of a variety of nuclei. All the models follow the same fitting protocol, except for the assumed and presently unknown value of the neutron skin thickness of 208Pb. This enables one to tune the density dependence of the symmetry energy without compromising the success in reproducing well known physical observables. We found that the ongoing PREX-II and upcoming CREX campaigns at Jefferson Lab will play a vital role in constraining the weak form factor of xenon and argon, liquid noble gases that are used for the detection of both neutrinos and dark matter particles. We concluded that remarkable new advances in experimental physics have opened a new window into ground state densities of atomic nuclei using solely electroweak probes. The diversity and versatility of these experiments reveal powerful correlations that impose important nuclear structure constraints. In turn, these constraints provide quantitative theoretical uncertainties that are instrumental in searches for new physics and insights into the behavior of dense matter.

Search for exotic features in the ground state light nuclei with 10 ≤Z ≤ 18 from stable valley to drip lines

We present a systematic description of the exotic features in the ground states of light nuclei from the stable valley to the drip lines. A study with the even and odd isotopes of Ne, Mg, Si, S and Ar has been performed using theoretical formalisms (i) Relativistic mean-field plus state-dependent BCS approach and (ii) Macroscopic–Microscopic (MM) approach using the triaxially deformed Nilsson–Strutinsky Method. The computed binding energies and one- and two-neutron separation energies using both the theories show magic character of [Formula: see text] and 40. The neutron and proton radii and the neutron densities show a well-developed neutron skin in the neutron-rich isotopes. The exotic phenomena such as weakly bound structures and the central density depletion characterized as bubble effect are explored. Our calculations for the single particle levels, density profiles and the charge form factors indicate bubble-like structures. Few new candidates of bubble nuclei are identified. Most of the nuclei in this region are found deformed with mostly prolate shape and few triaxial shapes while many nuclei exhibit the phenomenon of shape coexistence. Our results display a reasonable agreement between both the theories and the available experimental data.

Neutron rich matter in the laboratory and in the heavens after GW170817

The historic observations of the neutron star merger GW170817 advanced our understanding of r-process nucleosynthesis and the equation of state (EOS) of neutron rich matter. Simple neutrino physics suggests that supernovae are not the site of the main r-process. Instead, the very red color of the kilonova associated with GW170817 shows that neutron star (NS) mergers are an important r-process site. We now need to measure the masses and beta decay half-lives of very neutron rich heavy nuclei so that we can more accurately predict the abundances of heavy elements that are produced. This can be done with new radioactive beam accelerators such as the Facility for Rare Isotope Beams (FRIB). GW170817 provided information on the deformability of NS and the equation of state of dense matter. The PREX II experiment will measure the neutron skin of 208Pb and help constrain the low density EOS. As the sensitivity of gravitational wave detectors improve, we expect to observe many more events. We look forward to exciting advances and surprises!

Coherent-nuclear pion photoproduction and neutron radii

{ {\bf Background:} Knowing the difference between the neutron and proton densities of nuclei is a significant topic because of its importance for understanding neutron star structures and cooling mechanisms. The coherent-nuclear photoproduction of pions, $({\g,\pi^0})$, combined with elastic electron scattering, has been suggested to be a very accurate probe of density differences. {\bf Purpose:} Study the ${(\g,\pi^0})$ reaction mechanism so as to better access the uncertainties involved in extracting the neutron density. {\bf Methods:} Include the effects of final-state pion-nucleus charge-exchange reactions on the cross section and study the influence of the non-zero spatial extent of the proton. {\bf Results:} The effects of final-state charge-exchange increase the cross section between 6\% and 5\%, generally decreasing as the momentum transfer increases. This leads to an increase of the extracted neutron skin distance by about 50\%. The validity of the previous treatments of the proton size is confirmed. {\bf Conclusion:} The model dependence of the theoretically computed cross section increases the total systematic uncertainty (experiment plus theory) in extracting the neutron skin from the ${(\g,\pi^0})$ cross section by at least a factor of three. }

Neutron skin in CsI and low-energy effective weak mixing angle from COHERENT data

Both the neutron skin thickness $\Delta R_{np}$ of atomic nuclei and the low-energy neutrino-nucleon ($\nu N$) interactions are of fundamental importance in nuclear and particle physics, astrophysics as well as new physics beyond the standard model (SM) but largely uncertain currently, and the coherent elastic neutrino-nucleus scattering (CE$\nu$NS) provides a clean way to extract their information. New physics beyond the SM may cause effectively a shift of the SM weak mixing angle $\theta_W$ in low-energy $\nu N$ interactions, leading to an effective weak mixing angle $\theta^*_W$. By analyzing the CE$\nu$NS data of the COHERENT experiment, we find that while a one-parameter fit to the COHERENT data by varying $\Delta R_{np}$ produces $\Delta R^{\rm{CsI}}_{np} \simeq 0.68^{+0.91}_{-1.13}$ fm for CsI with an unrealistically large central value by fixing $\sin^2 \theta^*_W$ at the low-energy SM value of $\sin^2\theta_W^{\rm{SM}} = 0.23857$, a two-dimensional fit by varying $\Delta R_{np}$ and $\sin^2 \theta^*_W$ leads to a strong positive correlation between $\Delta R_{np}$ and $\sin^2 \theta^*_W$ with significantly smaller central values of $\Delta R^{\rm {CsI}}_{np} \simeq 0.24_{-2.03}^{+2.30}$ fm and $\sin^2 \theta^*_W = 0.21_{-0.10}^{+0.13}$. Although the uncertainty is too large to claim a determination of $\Delta R^{\rm{CsI}}_{np}$ and $\sin^2 \theta^*_W$, the present study suggests that the multi-dimensional fit is important in future analyses of high-precision CE$\nu$NS data. The implication of the possible deviation of $\sin^2 \theta^*_W$ from $\sin^2\theta_W^{\rm{SM}}$ on new physics beyond the SM is also discussed.

A systematic study of the ground state properties of W, Os and Pt isotopes using HFB theory

A systematic study of the ground state properties of transitional nuclei W, Os and Pt is conducted with the help of Skyrme–Hartree–Fock–Bogoliubov theory. Different Skyrme interactions are employed in the study. Two different bases, harmonic oscillator and transformed harmonic oscillator, are used in our investigation. 2[Formula: see text]-separation energy, charge radii, neutron and proton rms radii, neutron skin thickness and deformation parameter have been estimated. The results obtained are in good agreement with the available experimental values.

Dependence of atomic parity-violation effects on neutron skins and new physics

We estimate the relative contribution of nuclear structure and new physics couplings to the parity non-conserving spin-independent effects in atomic systems, for both single isotopes and isotopic ratios. General expressions are presented to assess the sensitivity of isotopic ratios to neutron skins and to couplings beyond standard model at tree level. The specific coefficients for these contributions are calculated assuming Fermi distribution for proton and neutron nuclear densities for isotopes of Cs, Ba, Sm, Dy, Yb, Pb, Fr, and Ra. The present work aims to provide a guide to the choice of the best isotopes and pairs of isotopes for conducting atomic PNC measurements.

A study of charge radii and neutron skin thickness near nuclear drip lines

We studied the charge radius, rms radius and neutron skin thickness Δrnp in even-even isotopes of Si, S, Ar and Ca and isotones of N = 20, 28, 50 and 82. The Δrnp in doubly-magic 48Ca, 68Ni, 120,132Sn and 208Pb nuclei has also been calculated. Theoretical calculations are done with the Hartree-Fock-Bogoliubov theory with the effective Skyrme interactions. Calculated theoretical estimates are in good agreement with the recently available experimental data. The charge radii for Si, S, Ar and Ca isotopes is observed to be minimum at neutron number N = 14. The theoretically computed results with UNEDF0 model parameterization of functional are reasonably reproducing the experimental data for Δrnp in 48Ca, 68Ni and 120,132Sn. The energy density functional of UNEDF1 model provides much improved result of Δrnp for 208Pb.