Valence Proton Research Articles

The γ-ray spectroscopy studies of low-spin structures in 210Bi and 206Tl using cold neutron capture reactions

The γ-coincidence studies of low-spin structures of 210Bi and 206Tl are presented. The 210Bi nucleus, populated in thermal neutron capture reaction, was investigated using EXILL HPGe array at Institut Laue-Langevin in Grenoble. The experimental results were compared to the shell-model calculations allowing to draw the conclusions on the nature of the low-spin excitations populated below the neutron binding energy in 210Bi (4.6 MeV). It has been found that some levels cannot be described by the valence proton and neutron couplings, but may arise from couplings of valence particles to the 3- octupole phonon of the doubly magic 208Pb core. Moreover, preliminary results of a low-spin structure measurements of 206Tl by the γ-coincidence technique, making use of the 205Tl(n,γ)206Tl reaction at the FIPPS prompt γ-ray spectroscopy facility of ILL are shown. The population of a large number of excited states of 206Tl above the ground state up to the neutron binding energy (at 6.5 MeV), within a few units of spin is expected. The analysis involving double and triple γ-coincidences and γγ-angular correlations will allow to significantly extend the experimental information on the energy and spin-parity of the levels in 206Tl. This will help shedding light on the proton-hole and neutron-hole couplings near the doubly magic core 208Pb.

Persistence of the Z=28 Shell Gap Around ^{78}Ni: First Spectroscopy of ^{79}Cu.

In-beam γ-ray spectroscopy of ^{79}Cu is performed at the Radioactive Isotope Beam Factory of RIKEN. The nucleus of interest is produced through proton knockout from a ^{80}Zn beam at 270 MeV/nucleon. The level scheme up to 4.6MeV is established for the first time and the results are compared to MonteCarlo shell-model calculations. We do not observe significant knockout feeding to the excited states below 2.2MeV, which indicates that the Z=28 gap at N=50 remains large. The results show that the ^{79}Cu nucleus can be described in terms of a valence proton outside a ^{78}Ni core, implying the magic character of the latter.

Charge radius of the 13N* proton halo nucleus with Halo Effective Field Theory

We evaluated the charge radius of the first excited state of 13N with halo Effective Field Theory (hEFT) at the low energies. The halo effective field theory without pion is used to examine the halo nucleus bound state with a large S-wave scattering length. We built Lagrangian from the effective core and the valence proton of the fields and obtained the charge form factor at Leading–Order (LO). The charge radius at leading order for the first excited state of the proton halo nucleus, 13N, has been estimated as rc= 2.52 fm. This result is without any finite-size contributions included from the core and the proton. If we consider the contributions of the charge radius of the proton and the core, the result will be [rC]13N*= 5.85 fm.

Systematic study of unfavored α -decay half-lives of closed-shell nuclei related to ground and isomeric states

In present work, the unfavored $\mathcal{\alpha}$ decay half-lives and $\mathcal{\alpha}$ preformation probabilities of closed shell nuclei related to ground and isomeric states around $Z=82$, $N=82$ and 126 shell closures are investigated by adopting two-potential approach from the perspective of valence nucleon (hole) and isospin asymmetry of the parent nucleus. The results indicate that $\mathcal{\alpha}$ preformation probability is linear dependence on $N_p N_n$ or $N_p N_n I$, the same as the case of favored $\mathcal{\alpha}$ decay in our previous work [X.-D. Sun \textit{et al.}, Phys. Rev. C 94, 024338 (2016)]. $N_p$, $N_n$, and $I$ represent the number of valence protons (holes), the number of valence neutrons (holes), and the isospin of the parent nucleus, respectively. Fitting the $\mathrm{\alpha}$ preformation probabilities data extracted from the differences between experimental data and calculated half-lives without a shell correction, we give two linear formulas of the $\mathcal{\alpha}$ preformation probabilities and the values of corresponding parameters. Based on the formulas and corresponding parameters, we calculate the $\mathrm{\alpha}$ decay half-lives for those nuclei. The calculated results can well reproduce the experimental data.

Effectively-truncated large-scale shell-model calculations and nuclei around 100Sn

This paper presents a short overview of a procedure we have recently introduced, dubbed the double-step truncation method, which is aimed to reduce the computational complexity of large-scale shell-model calculations. Within this procedure, one starts with a realistic shell-model Hamiltonian defined in a large model space, and then, by analyzing the effective single particle energies of this Hamiltonian as a function of the number of valence protons and/or neutrons, reduced model spaces are identified containing only the single-particle orbitals relevant to the description of the spectroscopic properties of a certain class of nuclei. As a final step, new effective shell-model Hamiltonians defined within the reduced model spaces are derived by way of a unitary transformation of the original large-scale Hamiltonian. A detailed account of this transformation is given and the merit of the double-step truncation method is illustrated by discussing few selected results for 96Mo, described as four protons and four neutrons outside 88Sr. Some new preliminary results for light odd-tin isotopes from A = 101 to 107 are also reported.

Systematic study of kinematic and dynamic moments of inertia of superdeformed bands with NpNn scheme

The systematics of kinematic moment of inertia J(1) and dynamic moment of inertia J(2) of superdeformed (SD) bands in A∼130, 150, 190 mass regions have been studied. We have obtained the values of J(1) and J(2) for all the SD bands observed in the A∼130, 150, 190 mass regions by using the experimental intraband E2 transition energies. The result of this work includes the variation of J(1) with the product of valence proton and neutron numbers (NpNn). The phenomenon of band mixing has been observed in the A∼130, 150 mass regions and band crossing has been observed in the A∼190 mass region. The systematics also includes the variation of J(2) with the product of valence proton and neutron numbers (NpNn). Evidence of staggering behaviour has been observed in all three A∼130, 150 and 190 mass regions. We present for the first time the variation of J(1) and J(2) of SD bands in the A∼130, 150, 190 mass regions with NpNn.

Cross section and astrophysical S-factor for [formula omitted] reaction with Halo Effective Field Theory at low-energies

We considered one of the proton halo nuclei candidates, 13N* nucleus, and calculated the cross section and astrophysical S-factor for 12C(p, γ)13N* reaction using halo effective field theory without pion (hEFT¬π). The halo effective field theory is used to examine the halo nucleus bound state with a large S-wave scattering length. We calculated the radiative proton capture cross section and the astrophysical S-factor from the fields of the core and the valence proton at the Leading-Order (LO). We showed that there is a good agreement among the our results for cross section and astrophysical S-factor of the 12C(p, γ)13N* reaction and the experimental data. The astrophysical S-factor that has been estimated at the zero energy (Ecm=0) by using a theoretical calculation of the cross section for direct radiative capture and an extrapolation of this calculation obtained S(0)=1.883×10−3 MeV-b.

Signatures of shell evolution in alpha decay across the N = 126 shell closure**Supported by National Natural Science Foundation of China (11375086, 11535004, 11605089, 11120101005), Natural Science Youth Fund of Jiangsu Province (BK20150762), Fundamental Research Funds for the Central Universities (30916011339), 973 National Major State Basic Research and Development Program of China (2013CB834400), and a Project Funded by the Priority

Within the alpha-cluster model, we particularly investigate the alpha decay of exotic nuclei in the vicinity of the N = 126 neutron shell plus the Z = 82 proton shell. The systematics of alpha-preformation probability (Pα), as an indicator of the shell effect, is deduced from the ratio of the experimental decay width to the calculated one. Through the comparative analysis of the Pα trend in the N = 124−130 isotonic chain, the N = 126 and Z = 82 shell closures are believed to strongly affect the formation of the alpha particle before its penetration. Additionally, the Pα variety in Po and Rn isotopes is presented as another proof for such an influence. More importantly, it may be concluded that the expected neutron (or proton) shell effect gradually fades away along with the increasing valence proton (or neutron) number. The odd-even staggering presented in the Pα value is also discussed.

Deuteron-Like Correlation for the T = 0 Channel in 18F Studied within the Continuum Contributions

We study the deuteron-like correlation of the valence proton and neutron for the T = 0 channel in 18F using the cluster-orbital shell model approach. In this study, the deuteron-like correlation is examined in terms of two key ingredients, cross-shell configuration and continuum contribution. We discuss the cross-shell configuration contributes to the restoration of the symmetry to form the LS-coupling in 1+, and the continuum contributions plays an important role of the spatial localization of the proton and neutron.

Identification of the one-quadrupole phonon [formula omitted] state of 204Hg

One-phonon states of vibrational nuclei with mixed proton–neutron symmetry have been observed throughout the nuclear chart besides the mass A≈200 region. Very recently, it has been proposed that the 22+ state of 212Po is of isovector nature. This nucleus has two valence protons and two valence neutrons outside the doubly-magic 208Pb nucleus. The stable isotope 204Hg, featuring two valence-proton and valence-neutron holes, with respect to 208Pb, is the particle-hole mirror of 212Po. In order to compare the properties of low-lying isovector excitations in these particle-hole mirror nuclei, we have studied 204Hg by using the projectile Coulomb-excitation technique. The measured absolute B(M1;22+→21+) strength of 0.20(2)μN2 indicates that the 22+ level of 204Hg is at least the main fragment of the 21,ms+ state. For the first time in this mass region, both lowest-lying, one-quadrupole phonon excitations are established together with the complete set of their decay strengths. This allows for a microscopic description of their structures, achieved in the framework of the Quasi-particle Phonon Model.

Electromagnetic Moments of Radioactive ^{136}Te and the Emergence of Collectivity 2p⊕2n Outside of Double-Magic ^{132}Sn.

Radioactive ^{136}Te has two valence protons and two valence neutrons outside of the ^{132}Sn double shell closure, providing a simple laboratory for exploring the emergence of collectivity and nucleon-nucleon interactions. Coulomb excitation of ^{136}Te on a titanium target was utilized to determine an extensive set of electromagnetic moments for the three lowest-lying states, including B(E2;0_{1}^{+}→2_{1}^{+}), Q(2_{1}^{+}), and g(2_{1}^{+}). The results indicate that the first-excited state, 2_{1}^{+}, composed of the simple 2p⊕2n system, is prolate deformed, and its wave function is dominated by excited valence neutron configurations, but not to the extent previously suggested. It is demonstrated that extreme sensitivity of g(2_{1}^{+}) to the proton and neutron contributions to the wave function provides unique insight into the nature of emerging collectivity, and g(2_{1}^{+}) was used to differentiate among several state-of-the-art theoretical calculations. Our results are best described by the most recent shell model calculations.

Microscopic method for E0 transition matrix elements

We present a microscopic model for electric monopole ($E0$) transition matrix elements by combining a configuration interaction model for orbital occupations with an energy-density functional model for the single-particle potential and radial wave functions. The configuration interaction model is used to constrain the orbital occupations for the diagonal and off-diagonal matrix elements. These are used in an energy-density functional calculation to obtain a self-consistent transition density. This density contains the valence contribution, as well as the polarization of the protons by the valence protons and neutrons. We show connections between $E0$ matrix elements and isomer and isotope shifts of the charge radius. The spin-orbit correction to the charge density is important in some cases. This model accounts for a large part of the data over a wide region of the nuclear chart. It also accounts for the shape of the observed electron scattering form factors. The results depend on the Skyrme parameters used for the energy-density functional and might be used to provide new constraints for them.

Interplay Between Particle and Core Excitations in $^{133}$Sb

The decay of the one-proton valence nucleus 133Sb is studied using the cold-neutron induced fission of 235U and 241Pu targets. The experiment is performed at the ILL reactor in Grenoble, using a highly efficient HPGe array, also coupled to fast LaBr3(Ce) scintillators. High-spin excited states above the 16.6 s isomer are observed, and the lifetime of the 13/2+ and 15/2+ states is measured by fast-timing techniques, revealing a complex nature of the wave functions. The experimental results are well-interpreted by a newly developed microscopic model which takes into account the coupling between the valence proton and excitations (both collective and noncollective) of the doubly magic 132Sn core.

Study of the two-proton halo nucleus 17Ne

The ([Formula: see text]Ne) nucleus is described as two protons outside of a deformed core. The Microscopic Cluster Model (MCM) is used to describe the three-body system [Formula: see text] with Jacobi coordinates. This model strongly exhibits the Coulomb effect and therefore it is used to explore the role of the Coulomb effect in proton halo formation. The main goal of this study is to confirm that [Formula: see text]Ne is a two-proton halo nucleus. In the calculations, the energy states (0[Formula: see text]), (1[Formula: see text]), (0[Formula: see text]) and (0[Formula: see text]) are considered to be occupied by two valence protons. Based on the comparison with other theoretical and experimental studies, the present MCM calculations show that the exotic structure of the valence protons is not evident in the halo structure of [Formula: see text]Ne.

Classical electromagnetic fields from quantum sources in heavy-ion collisions

Electromagnetic fields are generated in high energy nuclear collisions by spectator valence protons. These fields are traditionally computed by integrating the Maxwell equations with point sources. One might expect that such an approach is valid at distances much larger than the proton size and thus such a classical approach should work well for almost the entire interaction region in the case of heavy nuclei. We argue that, in fact, the contrary is true: due to the quantum diffusion of the proton wave function, the classical approximation breaks down at distances of the order of the system size. We compute the electromagnetic field created by a charged particle described initially as a Gaussian wave packet of width 1 fm and evolving in vacuum according to the Klein–Gordon equation. We completely neglect the medium effects. We show that the dynamics, magnitude and even sign of the electromagnetic field created by classical and quantum sources are different.

Distinction between elastic scattering of weakly bound proton- and neutron-rich nuclei: The case ofB8andBe11

Experimental data show that the elastic scattering cross sections of the neutron-rich nucleus $^{11}\mathrm{Be}$ are greatly reduced by the coupling effects from the breakup channels, while those of the proton-rich nucleus $^{8}\mathrm{B}$ are not. Such difference is found to persist in results of systematic calculations of $^{8}\mathrm{B}$ elastic scattering from $^{208}\mathrm{Pb}$ at 60 and 170.3 MeV and from $^{64}\mathrm{Zn}$ at 32 and 86 MeV, and $^{11}\mathrm{Be}$ elastic scattering from $^{208}\mathrm{Pb}$ at 55 and 143 MeV and from $^{64}\mathrm{Zn}$ at 29 and 66 MeV with the continuum-discretized coupled channel (CDCC) method. The Coulomb and centrifugal barriers experienced by the valence proton in the ground state of $^{8}\mathrm{B}$, which do not exist for the valence neutron in the ground state of $^{11}\mathrm{Be}$, are found to be the reason for such differences in the angular distributions of elastic scattering cross sections of these two weakly bound nuclei.

Systematic study of favoredα-decay half-lives of closed shell odd-Aand doubly-odd nuclei related to ground and isomeric states

In this work, we systematically investigate the favored $\ensuremath{\alpha}$-decay half-lives and $\ensuremath{\alpha}$ preformation probabilities of both odd-$A$ and doubly-odd nuclei related to ground and isomeric states around the doubly magic cores at $Z=82, N=82$ and at $Z=82, N=126$, respectively, within a two-potential approach from the view of the valence nucleon (or hole). The results show that the $\ensuremath{\alpha}$ preformation probability is linearly related to ${N}_{\text{p}}{N}_{\text{n}}$ or ${N}_{\text{p}}{N}_{\text{n}}I$, where ${N}_{\text{p}}, {N}_{\text{n}}$, and $I$ are the number of valence protons (or holes), the number of valence neutrons (or holes), and the isospin of the parent nucleus, respectively. Fitting the $\ensuremath{\alpha}$ preformation probabilities data extracted from the differences between experimental data and calculated half-lives without a shell correction, we give two analytic formulas of the $\ensuremath{\alpha}$ preformation probabilities and the values of corresponding parameters. Using those formulas and the parameters, we calculate the $\ensuremath{\alpha}$-decay half-lives for those nuclei. The calculated results can well reproduce the experimental data.

Structure of 23Al from a multi-channel algebraic scattering model based on mirror symmetry

The proton-rich nucleus 23Al has a ground state just 123 keV below the one-proton emission threshold, and as a result comparatively little is known experimentally about its properties, as with many such nuclei. Theoretical investigations have tended to model exclusively the ground and first one to three excited states known. In this paper, we theoretically model most of the known spectrum, and predict what states may as yet be unobserved. We use the multichannel algebraic scattering method to describe states as resonances of a valence proton coupled to a 22Mg rotor core. Six states with low-excitation energies and defined are matched, and we make the first prediction of the properties of four others and propound the possible existence of several more.

The mutable nature of particle-core excitations with spin in the one-valence-proton nucleus 133 Sb

The gamma-ray decay of excited states of the one-valence-proton nucleus 133Sb has been studied using cold-neutron induced fission of 235U and 241Pu targets, during the EXILL campaign at the ILL reactor in Grenoble. By using a highly efficient HPGe array, coincidences between gamma-rays prompt with the fission event and those delayed up to several tens of microseconds were investigated, allowing to observe, for the first time, high-spin excited states above the 16.6 micros isomer. Lifetimes analysis, performed by fast-timing techniques with LaBr3(Ce) scintillators, reveals a difference of almost two orders of magnitude in B(M1) strength for transitions between positive-parity medium-spin yrast states. The data are interpreted by a newly developed microscopic model which takes into account couplings between core excitations (both collective and non-collective) of the doubly magic nucleus 132Sn and the valence proton, using the Skyrme effective interaction in a consistent way. The results point to a fast change in the nature of particle-core excitations with increasing spin.

Change of nuclear configurations in the neutrinoless double-βdecay ofTe130→Xe130andXe136→Ba136

The change in the configuration of valence protons between the initial and final states in the neutrinoless double-$\beta$ decay of $^{130}$Te $\rightarrow$ $^{130}$Xe and of $^{136}$Xe $\rightarrow$ $^{136}$Ba has been determined by measuring the cross sections of the ($d$,$^3$He) reaction with 101-MeV deuterons. Together with our recent determination of the relevant neutron configurations involved in the process, a quantitative comparison with the latest shell-model and interacting-boson-model calculations reveals significant discrepancies. These are the same calculations used to determine the nuclear matrix elements governing the rate of neutrinoless double-$\beta$ decay in these systems.