A short history of nuclear magnetic moments and GT transitions

We summarize the history and our present understanding of nuclear magnetic moments and Gamow-Teller transitions.The roles of configuration mixing,meson exchange currents and relativistic effects are examined.Experimental evidence for the importance of tensor correlations is also discussed.     

Beta-NMR/ON on-line at the NICOLE facility, ISOLDE –recent magnetic moment studies near double magic 68Ni

The technique of β-NMR/ON and its use for measurement of nuclear magnetic moments is briefly reviewed. Recent magnetic moment measurements are reported on ⁶⁷Ni and ⁶⁷Cu. The relevance of magnetic moments of single-particle (hole) states for study of effects of configuration mixing and mesonic exchange currents is discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Configuration mixing and elastic magnetic electron scattering from nuclei

The role of configuration mixing in the analysis of recent elastic magnetic electron scattering experiments on ⁴⁹Ti, ⁵⁹Co, ⁸⁷Sr and ⁹³Nb is examined. In particular the dependence of the rms radius of the valence nucleon extracted from such analyses on the detailed nuclear configurations used is studied. In addition, the effects of meson-exchange currents together with configuration mixing are discussed. It is found that configuration mixing does play a significant role and that high-precision studies of elastic magnetic electron scattering should proceed beyond the framework of the extreme single-particle model.     

随机相互作用系综内的镉同位素电磁矩线性演化

在随机相互作用系综内,镉同位素11/2-同质异能态的电四极矩与磁偶极矩总是倾向于随中子数的增加呈线性演化,这与近年来的实验观测是一致的。除了对力对磁矩线性演化的决定性影响之外,特定形式的质子-中子相互作用被认为是这种线性演化的主要驱动力:电矩的线性演化要求质子中子之间的四极相互作用;磁矩则要求质子中子之间的短程相互作用,并且这种相互作用应具有与真实核相互作用一致的相对强度与正负性。In random-interaction ensembles, the electric quadrupole moments (Q) and magnetic moments (μ) of the Iπ=11/2- isomers of the Cd isotopes predominantly present linear correlation with neutron numbers, corresponding to the recently emphasized linear Q and μ systematics in realistic nuclear system. Although the seniority scheme enhances such predominance (more essentially for μ), the configuration mixing due to quadrupolelike and δ-force-like proton-neutron interactions is responsible for the linear Q and μ systematics, respectively, at least in random-interaction ensembles. Especially, the linear μ systematics further requires the proton-neutron interaction have similar relative strength and attractive-repulsive property to realistic nuclear interaction.     

Towards the nuclear matter-quark matter phase transition

Baryon magnetic moments are considered in the quark model. Small contributions to the moments are assumed to arise from configuration mixing (including configurations with orbital angular momentum) in the baryon wave functions, from SU (3) breaking, and from the dependence of the effective quark masses on their environment. It is found that these contributions can improve the agreement of the quark model with experiment. However, so long as quarks have Dirac magnetic moments, charge symmetry holds, and SU (3) breaking effects are small, there is a residual disagreement between predictions of the model and values of some of the recently measured hyperon magnetic moments.     

Magnetic moments of light nuclei

Magnetic moments of the nuclei ¹⁵N, ¹⁵O, ¹⁷O, ¹⁷F and ¹⁹F are investigated. The importance ; of configuration mixing as well as meson-exchange currents is discussed in detail. Meson-exchange currents are treated in the one-boson exchange limit. Short-range N-N correlations are obtained from solutions of the Bethe-Goldstone equation for doubly closed shell nuclei by the use of realistic N-N potentials which ensure a correct treatment of tensor correlations.     

Can we see relativistic and quark effects in nuclear magnetic moments?

Many theoretical contributions to nuclear magnetic moments are reviewed with major attention to core polarisation and meson exchange currents. Experimental evidence is drawn from light isobaric mirror nuclei. Relativistic and quark contributions to nuclear magnetic moments are estimated and discussed.     

Bohr–Weisskopf effect: influence of the distributed nuclear magnetization on hfs

Nuclear magnetic moments provide a sensitive test of nuclear wave functions, in particular those of neutrons, which are not readily obtainable from other nuclear data. These are taking added importance by recent proposals to study parity non-conservation (PNC) effects in alkali atoms in isotopic series. By taking ratios of the PNC effects in pairs of isotopes, uncertainties in the atomic wave functions are largely cancelled out at the cost of knowledge of the change in the neutron wave function. The Bohr–Weisskopf effect (B–W) in the hyperfine structure interaction of atoms measures the influence of the spatial distribution of the nuclear magnetization, and thereby provides an additional constraint on the determination of the neutron wave function. The added great importance of B–W in the determination of QED effects from the hfs in hydrogen-like ions of heavy elements, as measured recently at GSI, is noted. The B–W experiments require precision measurements of the hfs interactions and, independently, of the nuclear magnetic moments. A novel atomic beam magnetic resonance (ABMR) method, combining rf and laser excitation, has been developed for a systematic study and initially applied to stable isotopes. Difficulties in adapting the experiment to the ISOLDE radioactive ion beam, which have now been surmounted, are discussed. A first radioactive beam measurement for this study, the precision hfs of ¹²⁶Cs, has been obtained recently. The result is 3629.515(∼0.001) MHz. The ability of ABMR to determine with high precision nuclear magnetic moments in free atoms is a desideratum for the extraction of QED effects from the hfs of the hydrogen-like ions. We also point out manifestations of B–W in condensed matter and atomic physics. This revised version was published online in July 2006 with corrections to the Cover Date.     

Investigation of neutrino properties in experiments at nuclear reactors: Present status and prospects

The present status of experiments that are being performed at nuclear reactors in order to seek the neutrino masses, mixing, and magnetic moments, whose discovery would be a signal of the existence of physics beyond the Standard Model, is considered, along with their future prospects.     

Quadrupole moments of medium-weight and heavy hypernuclei with the NΛ configurations (N = p and n)

Using the shell model wave functions, we have studied quadrupole moments of medium-weight and heavy hypernuclei, and obtained the shell model values of quadrupole moments of NΛ systems ( N = p and n). With the use of the first-order perturbation theory, we have also estimated the configuration mixing effects on quadrupole moments of these NΛ hypernuclei. We show that the hyperon-induced configuration mixing effects are small and the nucleon-induced configuration mixing effects are large in many cases. Received: 22 February 2000 / Accepted: 2 August 2000     

193T1超形变带K=1/2的可能性

分析了脱耦合项对于原子核转动惯量的重要影响.总结了奇质量核K=1/2带转动惯量变化规律的新特点.在此基础上讨论了¹⁹³T1中3条新的超形变带的内部结构.目前尚无足够证据能够确认它们都是K=1/2带.     

New on-line NMR/ON nuclear magnetic dipole moments near 132Sn: I. At the shell closure: meson exchange current effects

Recent on-line nuclear orientation measurements of nuclear magnetic dipole moments by the method of NMR on oriented nuclei (NMR/ON) have yielded significant new odd-A moments. These include those closest to double magic ¹³²Sn, namely, ¹³³Sb [¹³²Sn plus one g_7/2+ proton] and ¹³³Te^m [¹³²Sn with a pair of g_7/2+ protons and one hole in the h_11/2- neutron sub-shell]. These close-to-double-magic results allow stringent tests of nuclear moment theory including, as main contributions to deviations from the simple free nucleon (Schmidt limit) values, configuration mixing in the nuclear wavefunction and mesonic exchange current modification to the dipole moment operator. Comparison with theoretical prediction, using established approaches to both these corrections, is discussed showing success in medium mass nuclei comparable to results previously established in light [to ⁴⁰Ca] and heavy [near ²⁰⁸Pb] nuclei. This revised version was published online in August 2006 with corrections to the Cover Date.     

Magnetic moment of hyperons in nuclear matter by using quark–meson coupling models

We calculate the magnetic moments of hyperons in dense nuclear matter by using relativistic quark models. Hyperons are treated as MIT bags, and the interactions are considered to be mediated by the exchange of scalar and vector mesons which are approximated as mean fields. Model dependence is investigated by using the quark–meson coupling model and the modified quark–meson coupling model; in the former the bag constant is independent of density and in the latter it depends on density. Both models give us the magnitudes of the magnetic moments increasing with density for most octet baryons. But there is a considerable model dependence in the values of the magnetic moments in dense medium. The magnetic moments at the nuclear saturation density calculated by the quark–meson coupling model are only a few percents larger than those in free space, but the magnetic moments from the modified quark–meson coupling model increase more than 10% for most hyperons. The correlations between the bag radius of hyperons and the magnetic moments of hyperons in dense matter are discussed.     

Static and dynamic quadrupole moments of high-spin isomers in the Pb-region

Quadrupole moments of high-spin isomers in the Pb-region are studied by using core polarization charges induced by the coupling of single-particle states to giant resonances. We found that the core polarization charges are enough to reproduce the observed quadrupole moments of the isotones with neutron number N=126 quantitatively without any intrinsic deformation. The mass number dependence of the quadrupole moments in the Rn-isotopes is also discussed by taking into account the configuration mixing involving the neutron excited first 2⁺ state.     

Nuclear orientation as a tool for studying the structure of very unstable nuclei

With the availability of modern isotope separator on-line systems it has become possible to make broad and systematic studies of low-energy low-spin nuclear structure. A vital ingredient in such a program is unique spin-parity assignments to all low-lying levels. A most desirable complement to spin-parity information is detailed spectroscopic information. Obtaining such information far from stability is difficult because of low activity production. Nuclear orientation provides a means for obtaining spin assignments usingsingles measurements. This is less demanding on source intensities than - angular correlation coincidence measurements. Further, nuclear orientation can provide information on magnetic moments and on multipole mixing ratios. A number of structural problems are discussed: the need for unique spin assignments in systematics schemes; the need to distinguish between E2+E0 and M1 transitions; the importance of measuring E2-M1 mixing ratios; and the value of magnetic moment information. Particular emphasis is placed on the desirability of obtaining such information in the neutron-deficient Pt, Au, Hg, Tl, Pb and Bi isotopes, based upon the experimental program at the UNISOR facility.Work supported in part by U.S.Dept. of Energy, Contract No. DE-AS05-80ER10599.     

Theoretical study of the magnetic moments and anisotropy energy of CoRh nanoparticles

The role of size, structure and chemical order on the magnetic moments and magnetic anisotropy energy (MAE) of CoRh nanoparticles are studied in the framework of a self-consistent real-space tight-binding method. Our results show that a Rh core in a geometry having a large surface/volume ratio and with Co–Rh mixing at the interface is the most likely chemical arrangement. A local analysis reveals that the orbital and spin moments at the Co–Rh interface are largely responsible for the increase of the magnetic moments and magnetic anisotropy. Moreover, the local moments induced at the Rh atoms, which amount to about 20% of the moment per Co atom [ μ_Rh = (0.2–0.3) μ_B] and the orbital moments of Co atoms play a crucial role on the interpretation of experiment. The results are discussed in the context of the interplay between chemical order and magnetic properties.     

Revision of spin echoes in pure nuclear quadrupole resonance

Goldman's spin-1/2 formalism has been used for describing the response of an I=3/2 spin system to a two-pulse sequence in a pure nuclear quadrupole resonance experiment. A detailed analysis of the polarization evolution and quadrupolar echo generation is carried out through the use of explicit expressions for secular homo- and heteronuclear dipolar interactions. In striking contrast with previous studies, it is predicted that Van Vleck's second moments governing a classical solid-echo or Hahn sequence differ from those obtained by equivalent means in magnetic resonance. In fact, it is shown that, although measured moments still complement each other, the combined use of standard sequences does not allow the separate determination of homo- and heteronuclear dipolar contributions to the linewidth, not even in an indirect manner. In this context, the importance and potential usefulness of a crossed coil probe are also briefly discussed.     

Magnetic moments and GT-type β-decay matrix elements in nuclei with a LS doubly closed shell plus or minus one nucleon

The magnetic moments and GT-type β-decay matrix elements of nuclei with an ¹⁶O core plus (minus) one nucleon and with a ⁴⁰Ca core plus(minus) one nucleon are studied from the point of view of configuration mixing in terms of second order perturbation theory. It is found that the effect of the mixing of highly excited configurations through a tensor force is essential to explain the large reduction of the GT-type β-decay matrix elements. It is also found that modulus of the isovector parts of the gyromagnetic ratio, g_τS and g_τl, are appreciably reduced by the configuration mixing.     

Magnetic moment measurement by nuclear orientation

This review deals with problems concerning ground and long-lived metastable states. The interest of magnetic moments in the knowledge of the nuclear configurations and the couplings is shown. Static, dynamic and transient orientations, and the angular distribution of the emitted radiation by oriented nuclei are discussed.Some problems involved in the extraction of magnetic moment values from low temperature nuclear orientation measurements will be discussed: combined magnetic and electric interactions, intermediate state perturbation, Knight shift, hyperfine anomaly, and thermal reorientation. Methods allowing to find the sign of the magnetic moment are also outlined.     

Surface alpha-clustering in the lead region

The effect of shell model configuration mixing on the reduced α-amplitude in heavy nuclei is investigated and discussed with respect to the question of α-clustering in nuclei. It is shown that extensive configuration mixing may enhance the α-amplitude under the Coulomb barrier by huge, largely arbitrary factors. In contrast to this the actual αclustering in the nuclear surface may well be described within the shell model including only relatively few configurations in the open shell.