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Background: Zr region is characterized by very rapid changes in the ground state structure of the nuclei. In particular, the onset of deformation when passing from $^{98}$Zr to $^{100}$Zr is one of the fastest ever observed in the nuclear chart. It has been probed both experimental and theoretically that certain low-lying excited states of Zr isotopes own different shapes than the ground state. Purpose: We intend to disentangle the interplay between the sudden changes in the ground state shape, i.e., the existence of a quantum phase transition, and the presence in the spectra of coexisting states with very different deformation, i.e., the presence of shape coexistence. Method: We rely on a previous calculation using the Interacting Boson Model with Configuration Mixing (IBM-CM) which reproduces in detail the spectroscopic properties of $^{96-110}$Zr. This IBM-CM calculation allows to compute mean-field energy surfaces, wave functions and any other observable related with the presence of shape coexistence or with a quantum phase transition. Results: We obtain energy surfaces and the equilibrium value of the deformation parameter $\beta$, the U(5) decomposition of the wave functions and the density of states. Conclusions: We confirm that Zr is a clear example of quantum phase transition that originates from the crossing of two configurations with a very different degree of deformation. Moreover, we observe how the intruder configuration exhibits its own evolution which resembles a quantum phase transition too., Comment: Accepted in Physical Review C

The mass region with A~100 and Z~40 is known to experience a sudden onset of deformation. The presence of the subshell closure $Z=40$ makes feasible to create particle-hole excitations at a moderate excitation energy and, therefore, likely intruder states could be present in the low-lying spectrum. In other words, shape coexistence is expected to be a key ingredient to understand this mass region. The aim of this work is to describe excitation energies, transition rates, radii, and two-neutron separation energies for the even-even 94-110Zr nuclei and, moreover, to obtain information about wave functions and deformation. The interacting boson model with configuration mixing will be the framework to study the even-even Zr nuclei, considering only two types of configurations: 0particle-0hole and 2p-2h excitations. On one hand, the parameters appearing in the Hamiltonian and in the E2 transition operator are fixed trough a least-squares fit to the whole available experimental information. On the other hand, once the parameters have been fixed, the calculations allow to obtain a complete set of observables for the whole even-even Zr chain of isotopes. Spectra, transition rates, radii, $\rho^2(E0)$, and two-neutron separation energies have been calculated and a good agreement with the experimental information has been obtained. Moreover, a detailed study of the wave function has been conducted and mean-field energy surfaces and deformation have been computed too. The importance of shape coexistence has been shown to correctly describe the A~100 mass area for even-even Zr nuclei. This work confirmed the rather spherical nature of the ground state of 94-98Zr and its deformed nature for 100-110Zr isotopes. The sudden onset of deformation in 100Zr is owing to the rapid lowering of a deformed (intruder) configuration which is high-lying in lighter isotopes., Comment: Submitted to PRC

The neutron-deficient mercury isotopes serve as a classical example of shape coexistence, whereby at low energy near-degenerate nuclear states characterized by different shapes appear. The electromagnetic structure of even-mass 182-188 Hg isotopes was studied using safe-energy Coulomb excitation of neutron-deficient mercury beams delivered by the REX-ISOLDE facility at CERN. The population of $ 0^{+}_{1,2}$01,2+, $ 2^{+}_{1,2}$21,2+and $ 4^{+}_{1}$41+states was observed in all nuclei under study. Reduced E2 matrix elements coupling populated yrast and non-yrast states were extracted, including their relative signs. These are a sensitive probe of shape coexistence and may be used to validate nuclear models. The experimental results are discussed in terms of mixing of two different configurations and are compared with three different model calculations: the Beyond Mean Field model, the Interacting Boson Model with configuration mixing and the General Bohr Hamiltonian. Partial agreement with experiment was observed, hinting to missing ingredients in the theoretical descriptions. The neutron-deficient mercury isotopes serve as a classical example of shape coexistence, whereby at low energy near-degenerate nuclear states characterized by different shapes appear. The electromagnetic structure of even-mass 182-188 Hg isotopes was studied using safe-energy Coulomb excitation of neutron-deficient mercury beams delivered by the REX-ISOLDE facility at CERN. The population of $ 0^{+}_{1,2}$01,2+, $ 2^{+}_{1,2}$21,2+and $ 4^{+}_{1}$41+states was observed in all nuclei under study. Reduced E2 matrix elements coupling populated yrast and non-yrast states were extracted, including their relative signs. These are a sensitive probe of shape coexistence and may be used to validate nuclear models. The experimental results are discussed in terms of mixing of two different configurations and are compared with three different model calculations: the Beyond Mean Field model, the Interacting Boson Model with configuration mixing and the General Bohr Hamiltonian. Partial agreement with experiment was observed, hinting to missing ingredients in the theoretical descriptions. ispartof: The European Physical Journal A - Hadrons and Nuclei vol:55 issue:8 pages:130-130 status: published

Direct mass measurements of the low-spin 3/2(-) and high-spin 13/2(+) states in the neutron-deficient isotopes Po-195 and Po-197 were performed with the Penning-trap mass spectrometer ISOLTRAP at ISOLDE-CERN. These measurements allow the determination of the excitation energy of the isomeric state arising from the nu i(13/2) orbital in Po-195,Po-197. Additionally, the excitation energy of isomeric states of lead, radon, and radium isotopes in this region were obtained from alpha-decay chains. These excitation energies complete the knowledge of the energy systematics in the region and confirm that the 13/2(+) states remain isomeric, independent of the number of valence neutrons.

Large-scale shell-model calculations for the even-even cadmium isotopes Cd-98-Cd-108 have been performed with the ANTOINE code in the pi(2p(1/2); 1g(9/2)).(2d(5/2); 3s(1/2); 2d(3/2); 1g(7/2); 1h(11/2)) model space without further truncation. Known experimental energy levels and B(E2) values could be well reproduced. Taking these calculations as a starting ground we analyze the deformation parameters predicted for the Cd isotopes as a function of neutron number N and spin J using the methods of model independent invariants introduced by Kumar [Phys. Rev. Lett. 28, 249 (1972)] and Cline [Annu. Rev. Nucl. Part. Sci. 36, 683 (1986)].

The level scheme of the neutron-deficient nuclide 168Os has been extended and mean lifetimes of excited states have been measured by the recoil distance Doppler-shift method using the JUROGAM \gamma-ray spectrometer in conjunction with the IKP K\"oln plunger device. The 168Os \gamma rays were measured in delayed coincidence with recoiling fusion-evaporation residues detected at the focal plane of the RITU gas-filled separator. The ratio of reduced transition probabilities B(E2;4_1^+ \rightarrow 2_1^+)/B(E2;2_1^+ \rightarrow 0_1^+) is measured to be 0.34(18), which is very unusual for collective band structures and cannot be reproduced by IBM-2 model calculations based on the SkM* energy-density functional.

Shape coexistence in nuclei appears to be unique in the realm of finite many-body quantum systems. It differs from the various geometrical arrangements that sometimes occur in a molecule in that in a molecule the various arrangements are of the widely separated atomic nuclei. In nuclei the various ''arrangements'' of nucleons involve (sets of) energy eigenstates with different electric quadrupole properties such as moments and transition rates, and different distributions of proton pairs and neutron pairs with respect to their Fermi energies. Sometimes two such structures will ''invert'' as a function of the nucleon number, resulting in a sudden and dramatic change in ground-state properties in neighboring isotopes and isotones. In the first part of this review the theoretical status of coexistence in nuclei is summarized. Two approaches, namely, microscopic shell-model descriptions and mean-field descriptions, are emphasized. The second part of this review presents systematic data, for both even- and odd-mass nuclei, selected to illustrate the various ways in which coexistence is observed in nuclei. The last part of this review looks to future developments and the issue of the universality of coexistence in nuclei. Surprises continue to be discovered. With the major advances in reaching to extremes of proton-neutronmore » number, and the anticipated new ''rare isotope beam'' facilities, guidelines for search and discovery are discussed.« less

An inverse kinematics Coulomb excitation experiment was performed to obtain absolute E2 and M1 transition strengths in 134Xe. The measured transition strengths indicate that the 2 3 + state of 134Xe is the dominant fragment of the one-phonon 2 1 , ms + mixed-symmetry state. Comparing the energy of the 2 1 , ms + mixed-symmetry state in 134Xe to that of the 2 1 , ms + levels in the N = 80 isotonic chain indicates that the separation in energy between the fully-symmetric 2 1 + state and the 2 1 , ms + level increases as a function of the number of proton pairs outside the Z = 50 shell closure. This behavior can be understood as resulting from the mixing of the basic components of a two-fluid quantum system. A phenomenological fit based on this concept was performed. It provides the first experimental estimate of the strength of the proton–neutron quadrupole interaction derived from nuclear collective states with symmetric and antisymmetric nature.

Background: The lead region, Po, Pb, Hg, and Pt, shows up the presence of coexisting structures having different deformation and corresponding to different particle-hole configurations in the Shell Model language. Purpose: We intend to study the importance of configuration mixing in the understanding of the nuclear structure of even-even Po isotopes, where the shape coexistence phenomena are not clear enough. Method: We study in detail a long chain of polonium isotopes, 190-208Po, using the interacting boson model with configuration mixing (IBM-CM). We fix the parameters of the Hamiltonians through a least-squares fit to the known energies and absolute B(E2) transition rates of states up to 3 MeV. Results: We obtained the IBM-CM Hamiltonians and we calculate excitation energies, B(E2)'s, electric quadrupole moments, nuclear radii and isotopic shifts, quadrupole shape invariants, wave functions, and deformations. Conclusions: We obtain a good agreement with the experimental data for all the studied observables and we conclude that shape coexistence phenomenon is hidden in Po isotopes, very much as in the case of the Pt isotopes., To be published in Physical Review C. arXiv admin note: text overlap with arXiv:1312.4595

We present an analytic solvable γ -periodic potential of the form μ / sin 2 ( 3 γ ) in the Bohr–Mottelson collective model. The choice allows for a separation in both β , γ and θ ι if the γ -variable in the moments of inertia is approximated by its expectation value γ 0 = π / 6 . Energy spectra, E2 transition rates and subsequent collective bands with their properties are presented. We compare the approximation of γ = γ 0 = π / 6 with a full diagonalisation of the rotational part. These results clearly point out that the approximative analytical treatment describes the full numerical results very well.

In a type II supernova explosion an enormous amount of (anti)neutrinos of all flavors is emitted. They are escaping from very close to the center of the star, carrying away by far the largest part of the gravitationally released energy. The terrestrial detection of these neutrinos would provide precious information on the supernova event. We present cross-section calculations for neutrino scattering off atomic nuclei. We show that investigating the polarization characteristics in nucleon-knockout reactions allows one to obtain extra information on the supernova neutrinos, and we discuss the energy sensitivity of neutrino-nucleus interactions as a supernova-neutrino probe.

Alpha-decay of the new nuclide 184Bi has been studied in the complete-fusion reaction 93Nb(94Mo, 3n)184Bi at the velocity filter SHIP. The evaporation residues were separated in-flight and subsequently identified on the basis of recoil- $\alpha$ , recoil- $\alpha$ - $\gamma$ analysis and excitation functions measurements. Two $\alpha$ -decaying isomeric states in 184Bi with half-life values of 13(2) ms and 6.6(1.5) ms were identified. The $\alpha$ -branching ratio of 180Tl was deduced for the first time as $b_\alpha = (2 --12)\%$ . Improved data on the fine-structure $\alpha$ -decay of 186Bi were obtained in the 93Nb(95Mo, 2n)186Bi reaction. A similarity of the decay energies and half-life values of 184,186Bi is pointed out and a possible explanation for this effect is suggested.

Detailed fine-structure $\alpha$ -decay studies of 188,190Bi were performed using the complete-fusion reactions of 50,52Cr ions with a 142Nd target at the velocity filter SHIP. The evaporation residues were separated in-flight and subsequently identified on the basis of recoil- $\alpha$ , recoil- $\alpha$ - $\gamma$ /X-ray and excitation function measurements. Improved data on the $\alpha$ -decay of 188,190Bi were obtained and a number of new low-lying excited states in the daughters 184,186Tl were observed. An intruder, presumably 10- state was identified in 184Tl, extending the systematics of such states in the odd-odd Tl nuclei beyond the neutron mid-shell at N = 104. Some technical aspects of experiment at recoil separators are also discussed.

Motivated by the proposed experiment $^{14}N(d,{^2He})^{14}C$, we study the final states which can be reached via the allowed Gamow-Teller mechanism. Much emphasis has been given in the past to the fact that the transition matrix element from the $J^{\pi}=1^+ T=0$ ground state of $^{14}N$ to the $J^{\pi}=0^+ T=1$ ground state of $^{14}C$ is very close to zero, despite the fact that all the quantum numbers are right for an allowed transition. We discuss this problem, but, in particular, focus on the excitations to final states with angular momenta $1^+$ and $2^+$. We note that the summed strength to the $J^{\pi}=2^+ T=1$ states, calculated with a wide variety of interactions, is significantly larger than that to the $J^{\pi}=1^+ T=1$ final states., Comment: Submitted to Phys. Rev. C

Over the past decades, quantum Monte Carlo methods have proven to be very valuable for the study of quantum-mechanical many-body systems. The basic ingredient of theses methods is a decomposition of the imaginary-time evolution operator into path integrals. These paths can then be sampled using Monte Carlo techniques. Though very successful for bosons, these methods often have troubles in dealing with fermions: the fermionic antisymmetry leads to a ‘sign problem’. One approach, the auxiliary-field method, has yielded slightly better results in dealing with the sign problem. Some recent developments on this method are highlighted. As a case study, it is applied to a pairing model for Fe nuclei, where indications are found for a phase transition related to nucleon–nucleon pairing.

We intend to provide a consistent description of the even-even Hg isotopes, 172-200Hg, using the interacting boson model including configuration mixing. We pay special attention to the description of the shape of the nuclei and to its connection with the shape coexistence phenomenon., Comment: To appear in CGS15 conference proceedings (EPJ Web of Conferences)

In an attempt to describe the excitation spectra and transitions strengths of light even-even Cd-isotopes (A = 98 - 108), large-scale shell-model calculations in the proton (2p(1/2), 1g(9/2)) and the neutron (2d(5/2), 1g(7/2), 2d(3/2), 3s(1/2), 1h(11/2)) model space were performed. Preliminary results are presented and discussed.

Coulomb-excitation experiments are performed with postaccelerated beams of neutron-deficient Po196,198,200,202 isotopes at the REX-ISOLDE facility. A set of matrix elements, coupling the low-lying states in these isotopes, is extracted. In the two heaviest isotopes, Po200,202, the transitional and diagonal matrix elements of the 2+1 state are determined. In Po196,198 multistep Coulomb excitation is observed, populating the 4+1,0+2, and 2+2 states. The experimental results are compared to the results from the measurement of mean-square charge radii in polonium isotopes, confirming the onset of deformation from Po196 onwards. Three model descriptions are used to compare to the data. Calculations with the beyond-mean-field model, the interacting boson model, and the general Bohr Hamiltonian model show partial agreement with the experimental data. Finally, calculations with a phenomenological two-level mixing model hint at the mixing of a spherical structure with a weakly deformed rotational structure., We acknowledge the support of the ISOLDE Collaboration and technical teams and, especially, the support of RILIS and REX. This work was supported by FWO-Vlaanderen (Belgium), by GOA/2010/010 (BOF KU Leuven), by the Interuniversity Attraction Poles Programme initiated by the Belgian Science Policy Office (BriX network P7/12), by the European Commission within the Seventh Framework Programme through I3-ENSAR (Contract No. RII3-CT-2010-262010), by the German BMBF under Contract Nos. 05P12PKFNE, 06DA9036I 05P12RDCIA, and 05P12RDCIB, by the UK Science and Technology Facilities Council, by the Spanish MINECO under Project No. FIS2011-28738-C02-02, by Narodowe Centrum Nauki (Polish Center for Scientific Research) Grant No. UMO-2013/10/M/ST2/00427, by the Academy of Finland (Contract No. 131665), and by the European Commission through the Marie Curie Actions call PIEFGA-2008-219174 (J.P.).

The recently measured spectroscopic quadrupole moments of the 11 − intruder isomers in 194,196 Pb are being discussed in the particle-core coupling model. The essential physics behind the nature of these isomers is revealed by a simple two-level-mixing calculation, showing that the coupling of the valence proton particles with vibrations of the underlying Hg core induces a factor of two increase of the quadrupole moments.

The evolution of the total energy surface and the nuclear shape in the isotopic chain $^{172-194}$Pt are studied in the framework of the interacting boson model, including configuration mixing. The results are compared with a self-consistent Hartree-Fock-Bogoliubov calculation using the Gogny-D1S interaction and a good agreement between both approaches shows up. The evolution of the deformation parameters points towards the presence of two different coexisting configurations in the region 176 $\leq$ A $\leq$ 186., Submitted to PRC

Mass measurements with the Penning-trap mass spectrometer ISOLTRAP at ISOLDE/CERN are extended to nonsurface ionizable species using newly developed ion-beam bunching devices. Masses of 179–197Hg, 196,198Pb, 197Bi, 198Po and 203At were determined with an accuracy of 1×10 −7 corresponding to δm≈20 keV. Applying a resolving power of up to 3.7×10 6 ground and isomeric states of 185,187,191,193,197Hg were separated. First experimental values for the isomeric excitation energy of 187,191Hg are obtained. A least-squares adjustment has been performed and theoretical approaches are discussed to model the observed fine structure in the binding energy.

Two excited J(pi)=0(+) states in Pb-186 populated in the a-decay of Po-190 have been identified through alpha -particle/conversion electron coincidences in an experiment at the velocity filter SHIP ...

In the present discussion we concentrate on shape coexistence as obtained within a deformed single particle field as well as starting from the spherical shell model, incorporating deformation effects via the residual proton–neutron quadrupole interaction. We discuss in particular the appearance of shape coexisting phenomena in the Pb region. In a second part then, we present a number of experimental fingerprints that are able to recognize the appearance of shape coexisting phenomena or of shape mixing through the use of selective experiments (e.g., band structure, spectroscopic factors, static moments, E0 properties and α-decay).

Electric monopole (E0) properties are studied across the entire nuclear mass surface. Besides an introductory discussion of various model results (shell model, geometric vibrational and rotational models, algebraic models), we point out that many of the largest E0 transition strengths, ϱ 2 (E0), are associated with shape mixing. We discuss in detail the manifestation of E0 transitions and present extensive data for single-closed shell nuclei, vibrational nuclei, well-deformed nuclei, nuclei that exhibit sudden ground-state changes, and nuclei that exhibit shape coexistence and intruder states. We also pay attention to light nuclei, odd- A nuclei, and illustrate a suggested relation between ϱ 2 (E0) and isotopic shifts.

The excitation energies of the single-particle normal and intruder levels in both 183Tl and 187Bi were measured for the first time via the α decay of 187Bi produced in the 97Mo(92Mo,pn)187Bi reaction. The previously unobserved 187Bi ground state (h9/2) to 183Tl ground state (s1/2) α transition was identified, establishing the 187Bi intruder state excitation energy to be 112(21) keV, 70 keV less than that of the same level in 189Bi.

A mean-field plus pairing model for atomic nuclei in the Fe region was studied using a finite-temperature quantum Monte-Carlo method. We present results for thermodynamical quantities such as the internal energy and the specific heat. These results give indications of a phase transition related to the pairing amongst nucleons, around temperatures of 0.7 MeV. The influence of the residual interaction and of the size of the model space on the nuclear level densities is discussed too., Comment: 23 pages, including 17 eps figures

On-line low temperature nuclear orientation (OLNO) experiments have been performed on the odd-A Te isotopes 131Te and 133Te using the technique of nuclear magnetic resonance on oriented nuclei (NMR/ON). The magnetic moments of the isomeric 11 2 − states have been measured extending the known data on these states in the Te isotopes up to the neutron shell closure at N = 82. The contribution to the 11 2 − magnetic moment in 133Te due to core polarisation is calculated using an RPA shell model as well as corrections to the magnetic dipole operator caused by mesonic exchange currents. The neutron number dependence of the magnetic moments of the 11 2 − isomers in heavy Te isotopes is discussed in terms of particle-core coupling model (PCM) calculations.

We show that, within a two-group schematic random phase approximation model, a concentration of local dipole strength in the lower tail region of the electric giant dipole resonance can show up. The model is tested under more realistic circumstances for the isovector 1${}^{\ensuremath{-}}$ states in ${}^{116}$Sn.

In this paper a review is given of a class of sub-models of both approaches, characterized by the fact that they can be solved exactly, highlighting in the process a number of generic results related to both the nature of pair-correlated systems as well as collective modes of motion in the atomic nucleus., 34 pages, 8 figures accepted for publication in Scholarpedia

Coulomb Displacement Energies (CDE) are accurately known for a wide range of nuclear masses. Assuming isospin independence in the nuclear Hamiltonian, the CDE can in first instance be interpreted as the Coulomb interaction energy between the density of the excess neutrons and the proton charge density in the parent nucleus. However, when using reasonable meanfield models for the proton and neutron density one underestimates the CDE by about 8% on average. This discrepancy is known as the Nolen-Shiffer anomaly, and various explanations have been put forward in the past. In this work we reexamine the role of nucleon-nucleon correlations. We present calculations for the pair density functions in various nuclei. Preliminary results suggest that the modifications to the mean-field pair density functions cause an enhancement of the CDE in the order of 4%, which is ratherA-independent.

We apply the group theoretical concepts of the EIBM, an extension of the interacting boson model where a distinction is made between particle and hole bosons, to the particular situation of two coexisting systems in the same nucleus exhibiting the O(6) (regular states) and SU(3) (intruder states) symmetries. Besides giving evidence that such a coexisting set of states could well be applicable to the Pb region, we discuss the “global” symmetry properties of the above model. We also concentrate on mixing between the otherwise coexisting symmetries and point out how to make more realistic calculations. We discuss, at large, the experimental evidence in the Pb region for intruder analog multiplets.

In this paper arguments are given that the nuclear temperature might be an important parameter for the calculation of neutrino-nucleus scattering cross sections relevant for supernova processes. We describe how this influence can be studied using the shell-model monte-carlo method (SMMC).

A technique to deal with Coulomb electron distortions in the analysis of (e,e{sup {prime}}p) reactions is presented. Thereby, no approximations are made. The suggested technique relies on a partial-wave expansion of the electron wave functions and a multipole decomposition of the electron and nuclear current in momentum space. In that way, we succeed in keeping the computational times within reasonable limits. This theoretical framework is used to calculate the quasielastic (e,e{sup {prime}}p) reduced cross sections for proton knockout from the valence shells in {sup 16}O, {sup 40}Ca, {sup 90}Zr, and {sup 208}Pb. The final-state interaction of the ejected proton with the residual nucleus is treated within an optical potential model. The role of electron distortion on the extracted spectroscopic factors is discussed. {copyright} {ital 1997} {ital The American Physical Society}

The magnetic moments of ( $\mathrm{double}\mathrm{magic}+1\mathrm{proton}$) nuclei having a ``jack-knife'' $j\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}l\ensuremath{-}s$ configuration form crucial tests for the theoretical treatment of mesonic exchange currents and core polarization effects in finite nuclei. The reported precision measurement and analysis of the magnetic moment of ${}^{133}\mathrm{Sb}$ ( ${}^{132}\mathrm{Sn}+\mathrm{one}{g}_{7/2}\mathrm{proton}$) $\ensuremath{\mu}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}3.00(1){\ensuremath{\mu}}_{N}$ provides the first such test in medium-heavy nuclei. In addition, new data on the N dependence of the ${7/2}^{+}{}^{123\ensuremath{-}133}\mathrm{Sb}$ ground state moments are presented. Analysis in terms of particle-core coupling indicates slightly negative collective g factors of heavy Sn core nuclei.

The reaction 148 Sm(p,t) 146 Sm was studied at E p = 26 MeV. Fifty-six excited states in the final N = 84 nucleus were observed below E exc = 4.2 MeV and their angular distributions were measured at 8 angles. Spin and parity assignments are made for 37 of them, based on the determination of the transferred angular momentum L . Ten excited J π = 0 + states were identified. The emerging excitation energies of the J π = 0 + states and the monopole strength distribution in 146 Sm are compared with those observed in nearby nuclei and with results of calculations done in the framework of the Particle-Core Coupling Model. The main features of the experimental results are interpreted using a superposition of two types of configurations: two-particle states coupled to the collective excitations of the N = 82 core and two holes coupled to the collective excitations of the N = 86 core. Calculations show also that two-phonon⊗two-particle configurations are spread over many states and their identification becomes difficult.

The structure of the low-lying levels in the mirror nuclei {sup 57}Ni and {sup 57}Cu is described within the extended unified model. The problem of single-particle energies in {sup 56}Ni is treated in detail. {open_quote}{open_quote}Bare{close_quote}{close_quote} single-particle energies are extracted from existing experimental data for the energy levels in {sup 57}Ni and {sup 57}Cu by carefully considering the influence of the coupling to excitations of the core. Important contributions arise, influencing especially the results on the spin-orbit splitting. The differences between the Coulomb energy shifts of various orbitals in {sup 56}Ni are discussed and compared with those resulting from Hartree-Fock calculations carried out using a broad range of Skyrme interactions. The parameters of the Woods-Saxon potential reproducing these neutron {open_quote}{open_quote}bare{close_quote}{close_quote} single-particle energies and the charge root-mean-square radius of {sup 56}Ni are extracted. It is demonstrated that the contributions associated with the Thomas-Ehrman effect and the electromagnetic spin-orbit interaction are important and large enough to account for the differences between the Coulomb energy shifts of the single-particle levels in {sup 56}Ni. {copyright} {ital 1996 The American Physical Society.}

The radioactive isotope 107In was studied using sub-barrier Coulomb excitation at the REX-ISOLDE facility at CERN. Two γ rays were observed during the experiment, corresponding to the low-lying 11/2+ and 3/2− states. The reduced transition probability of the 11/2+ state was determined with the semiclassical Coulomb excitation code GOSIA2. The result is discussed in comparison to large-scale shell-model calculations, previous unified-model calculations, and earlier Coulomb excitation measurements in the odd-mass In isotopes. ispartof: Physical Review C, Nuclear Physics vol:87 issue:1 status: published

A fully relativistic, gauge invariant and unitary pion photoproduction model is constructed including π, ϱ, ω, N and Δ degrees of freedom. The model is compared in detail to pion photoproduction observables in view of several sets of high-quality data that were obtained through the Δ resonance region in recent years. Starting from the relativistic model, a non-relativistic model mean ffor calculations in the nuclear medium is derived. The non-relativistic model is constructed to satisfy unitarity and is applied to both charged and neutral pion photoproduction with the same parameter set.

The concept of the atomic nucleus being characterized by an intrinsic property such as shape came as a result of high precision hyperfine studies in the field of atomic physics, which indicated a non-spherical nuclear charge distribution. Herein, we describe the various steps taken through ingenious experimentation and bold theoretical suggestions that mapped the way for later work in the early 50s by Aage Bohr, Ben Mottelson and James Rainwater. We lay out a long and winding road that marked, in the period of 50s to 70s, the way shell-model and collective-model concepts were reconciled. A rapid increase in both accelerator and detection methods (70s towards the early 2000s) opened new vistas into nuclear shapes, and their coexistence, in various regions of the nuclear mass table. Next, we outline a possible unified view of nuclear shapes: emphasizing decisive steps taken as well as questions remaining, next to the theoretical efforts that could result in an emerging understanding of nuclear shapes, building on the nucleus considered as a strongly interacting system of nucleons as the microscopic starting point.

We discuss the experimental evidence for many-particle many-hole excitations (mp-nh) at and near to closed shells. Besides a shell-model approach and in order to understand the salient features of the general behaviour of the 0+ intruder band heads, we mainly concentrate on a group theoretical classification. Using the boson model, various possibilities to classify intruder mp-nh excitations can be shown to exist. Ample evidence for the realization of these new symmetries is given in (i) the Z = 50 mass region and, in (ii) the Z = 82 Pb mass region. Finally, a possible extension to encompass also mp-nh excitations in light nuclei is presented.

We report on a quantitative study of the evolution of the nuclear shell structure, in particular, effective single-particle energies (ESPEs), based on the spin-tensor decomposition of an effective two-body shell-model interaction. While the global trend of the ESPEs is mainly due to the central term of the effective interaction, variations of shell gaps invoke various components of the in-medium NN force. From a detailed analysis of a well-fitted realistic interaction in the sdpf shell-model space, two most important contributions for the evolution of the N = 20 and N = 28 shell gaps are confirmed to be the central term and the tensor term. The role of the latter is dominant to explain the energy shift of spin-orbit partners. Spin-tensor analysis of microscopic effective interactions in sd, pf, and gds shell-model spaces, contrasted with that of the phenomenologically adjusted ones, shows no evidence of amplification of the tensor component contribution; however, it points toward the neglect of three-body forces in the present microscopic interactions.

The g-factors of the 217, 523 and 761 keV levels in 79 Br have been measured using Coulomb excitation of 79 Br beams and transient field technique with Gd as ferromagnetic host. Lifetimes of several states have been determined using the Doppler-shift attenuation method. Mixing ratios of γ-transitions were deduced from measured angular correlations. The data are discussed in the framework of the weak particle-core coupling and the particle-axial-rotor coupling models.

In nuclear resonance fluorescence experiments with unpolarized and linearly polarized bremsstrahlung we have observed for the first time very strong electric dipole transitions at about 3.5 MeV in the spherical, semi magic 116 Sn and 124 Sn nuclei. These transitions can be attributed to possible two phonon 2 + ⊗ 3 − excitations. The measured transition strengths are compared to the results of a QRPA calculation.

A simple necessary and sufficient condition which tells when an A-particle fermion wavefunction can be written as a Slater determinant is proven.

In this paper, we show that, although the spectroscopic properties of the monopole pairing force and a zero-range delta-function interaction are very similar, their saturation properties are quite different. In particular, the predictions for binding energies when filling up a major shell are radically different past mid-shell. This has significant consequences for understanding the masses and binding energies of long isotopic chains of nuclei that will be accessible with advanced exotic beam facilities.