Nuclear moments and charge radii of rare-earth isotopes studied by collinear fast-beam laser spectroscopy

The collinear fast-beam laser technique is being used to measure systematically hyperfine structures and isotope shifts of unstable nuclides in the rare-earth region. This brief report gives a general survey of the results obtained for the even-Z elements₆₄Gd,₆₆Dy,₆₈Er and₇₀Yb, with emphasis on the nuclear spins and moments. They allow a rather complete mapping of the single-particle structure and the development of nuclear deformation in the N > 82 region. The spins, magnetic moments and spectroscopic quadrupole moments of^159–169Yb are presented in detail.On leave from Bhabha Atomic Research Centre, Bombay, India.On leave from Institut für Physik, Mainz, Fed. Rep. of Germany.This work has been supported financially by the Deutsche Forschungsgemeinschaft and the Bundesministerium für Forschung und Technologie.     

Laser spectroscopy of exotic RI atoms in superfluid helium—OROCHI experiment

We have been developing a new laser spectroscopic technique “OROCHI,” which is based on the combination of superfluid helium as a stopper of radioactive isotope (RI) beam and in-situ laser spectroscopy of RI atoms, for determining spins and moments of exotic RIs. By using this unique technique, it is feasible to measure nuclear spins and electromagnetic moments of extremely low yield RI (estimated as less than 1 pps). Recently, we have demonstrated that nuclear spins and moments are obtained from Zeeman and hyperfine splittings of stable Rb isotopes measured using this OROCHI technique. Details of this laser spectroscopy method in He II “OROCHI” and the summary of our development are presented.     

Nuclear moments from laser spectroscopy

The systematic laser spectroscopy measurements of nuclear spins, moments and charge radii from hyperfine structures and isotope shifts are reviewed from a methodical point of view. Examples are given for the typical experimental approaches and their results. Laser spectroscopy methods of direct nuclear g-factor measurement have interesting features in common with the low-temperature nuclear orientation technique. These are described in some detail and discussed in their particular physics context.     

Localized canting of spins structure in the spinel oxide system: ZnzTizFe2−x−zCrx−zCoO4

The spinel oxide system Zn_zTi_zFe_2−x−zCr_x−zCoO₄; z=x²; x=0.60, 0.65, 0.70 and 0.80, was studied using neutron diffraction technique, low field DC magnetization measurements (ZFC–FC measurements), magnetic hysterisis, Mössbauer spectroscopy and low field AC susceptibility measurements. All the compositions show significantly less B-site magnetic moments at 10 K temperature derived from neutron diffraction data than the free ions site moments deduced assuming collinear arrangement of spins. This combined with some other features seen in the low temperature neutron diffraction patterns suggest localized canting of spins (LCS) type of magnetic ordering in the present system where a long range order of longitudinal component of moments co-exists along with totally disordered transverse component of moments. The conclusion is also supported by the features seen in the other measurements. The magnetic moments derived from 10 K neutron diffraction data are explained using the LCS approach for different exchange integrals ratios.     

Collinear laser spectroscopy on unstable isotopes—A tool of nuclear physics

Atomic hyperfine structures and isotope shifts yield basic information about nuclear ground-state spins, moments and mean square charge radii. Recently, the collinear-beam laser experiments at ISOLDE have considerably enlarged the range of elements for which these studies can be extended into regions far from β-stability. The essential features of these experiments are outlined, and examples of the results on the rare-earth and radium isotopic chains are given. Finally, further improvements in sensitivity using non-optical detection are discussed.     

Spectral moments for systems described by an ensemble of hamiltonians

We generalize Van Vleck's method of moments for disordered solid-state that can be described by an ensemble of hamiltonians. Special reference is made to N.M.R. spectroscopy. Inhomogeneous broadening for a sample of free spins and the more complex problem of interacting spins are discussed in detail. The cumulant expansion and the Liouville space formalism are introduced as tools to simplify the expressions for the moments and to obtain physical approximations. As a particular application the Sherrington-Kirkpatrick model for spin glasses is derived and interpreted physically.     

Spectroscopic properties of fission isomers

Our present understanding of the spectroscopic properties of fission isomers is discussed. Recent progress has been achieved by applying newly developed and improved experimental techniques such as the charge plunger method and the recoil shadow technique to measure quadrupole moments, moments of inertia, and spins of fission isomeric states. The data establish the evidence for shape isomerism in the actinide region and a second minimum in the fission potential.     

Line shapes of multiple quantum NMR coherences in one-dimensional quantum spin chains in solids

General formulae for intensities of multiple quantum (MQ) NMR coherences in systems of nuclear spins coupled by the dipole-dipole interactions are derived. The second moments of the MQ coherences of zero- and second orders are calculated for infinite linear chains in the approximation of the nearest neighbor interactions. Supercomputer simulations of intensities of MQ coherences of linear chains are performed at different times of preparation and evolution periods of MQ NMR experiments. The second moments obtained from the developed theory are compared with the results of the supercomputer analysis of MQ NMR dynamics. The linewidth information in MQ NMR experiments is discussed.     

On the theory of NMR spin echoes in solids

A general expression in terms of two-time correlation functions is derived for the spin echo responses to 90°-τ-β⁰_φ pulse sequences of quadrupolar spins coupled through dipolar interactions. The second moments of the correlation function are calculated for a system of spin one nuclei and shown to be in accordance with the experimental observations. Furthermore, results are presented for the fourth moments.     

Collinear laser spectroscopy of neutron-rich Cs isotopes at an on-line mass separator

High-resolution laser spectroscopy was carried out in fast atomic beams of ^{133,137,138,139}Cs, yielding hyperfine structure and isotope shift in the 455.5 nm resonance line. Nuclear moments and changes of mean-square radii are derived from the results.     

Relativistic recoil and spin corrections to atomic and Coulomb wave functions

A new wave equation for the relativistic two-body problem is derived and shown to be equivalent to the Breit equation and also to the “quasipotential” equation. Its unique advantage is that it provides analytic wave functions for arbitrary combinations of masses, spins, magnetic and higher moments of the two particles. Various applications are indicated, including an improvement of Dirac wave functions at small distances.     

Enforcing Thermal Entanglement of Three Coupled Qubits by Dissipation

The stationary state entanglement in a chain with three spins is reported. Each of spins couples to its own separate bosonic reservoir. The master equation for such spins’ system is derived under the Born-Markovian approximation. The result presents that the coupling between the middle spin and its bosonic bath in some special temperature region reinforce the entanglement between the spins. By analyzing the heat current between the middle spin and its bosonic bath, we find a tight relationship between the direction of heat current from the middle spin to its bosonic bath and the reinforcement of the entanglement. The entanglement increases with the heat current between the middle spin and its bosonic bath almost linearly.     

On Line Nuclear Orientation: Opportunity and challenge

The development of the On-Line Nuclear Orientation (OLNO) technique is reviewed. The present potential of the technique is discussed in the light of the attainable temperatures, the use of ion implantation and the required isotope flux. Limitations associated with spin-lattice relaxation are considered in some detail and a survey of accessible nuclei is presented. An outline comparison is given between OLNO and other methods for producing orientation of nuclei, for measuring nuclear spins and static moments and for the study of level structure and transition probabilities. The conclusion is drawn that the method in its present form has extensive potential over a wide range of nuclei. Future prospects for in-beam polarisation giving access to nuclei of shorter half lives are referred to briefly.     

The Second Moments of the Line Shapes of Multiple Quantum NMR Coherences in One-Dimensional Systems

The second moments of the line shapes of the zeroth- and second-order multiple quantum NMR coherences determined by the dipole–dipole interactions of nuclear spins in crystals have been calculated. The second moments determined by the zz part of the dipole–dipole interaction have been derived both by a direct calculation and based on the exact solution (in terms of the zz model) for the decay of the multiple quantum coherence intensities on the evolution period of a multi-quantum NMR experiment. The decay of the multiple quantum NMR coherence intensities in a single crystal of calcium fluorapatite is well described by the Gaussian curves with the calculated second moments.     

Optical transitions in antiferromagnets in the saturated paramagnetism region

The behaviour of the spins of the photoexcited ions and its nearest antiferromagnetic neighbours in a two-sublattice antiferromagnet with isotropic Heisenberg interaction in the saturated paramagnetism region has been theoretically studied. It has been shown that the magnetic moments of the ions may be oriented in this region noncollinear to the magnetic field in the case whether the exchange integral in the excited state is larger than in the ground state or there is strong uniaxial single-ion “easy plane” anisotropy in the excited state. The exciton-magnon transitions intensity may, as a result, also alter in the saturated paramagnetism region.     

用于核物理研究的精密激光谱技术的发展和展望

原子核基本性质（自旋、质量、寿命、磁矩、电四极矩和电荷半径等）与原子核的内在结构密切相关,是检验和发展原子核理论模型的重要依据。实验上可以通过多学科交叉的精密激光谱技术测量原子核外电子的超精细结构和同位素移位,来模型独立地提取原子核的自旋、磁矩、电四极矩和电荷均方根半径等多个核物理参量。这些基本性质的系统测量可以用于探索不稳定原子核中展现出来的新奇的物理现象与规律。近年来,为了测量产额更低的丰中子核的基本性质,激光谱技术不断更新和发展,以实现高分辨、高效率测量。本文详细介绍了激光谱测量的基本原理以及由此发展起来的用于不稳定原子核结构研究的各类互补的激光谱学技术,如共线激光谱（高分辨率低灵敏度）、在源激光谱（高灵敏度低分辨率）、共线共振电离谱（高分辨率高灵敏度）等激光谱技术,以及在不同核区的测量优势和局限。最后结合我国正在发展和规划中的新一代放射性核束装置,讨论精密激光谱技术在国内的发展以及在核物理研究中的应用。     

Nuclear Radiation Detected Optical Pumping of neutron-deficient Hg isotopes

The extension of the Nuclear Radiation Detected Optical Pumping method to mass-separated samples of isotopes far off stability is presented for a series of light Hg isotopes produced at the ISOLDE facility at CERN. The isotope under investigation is transferred by an automatic transfer system into the optical pumping apparatus. Zeeman scanning of an isotopically pure Hg spectral lamp is used to reach energetic coincidence with the hyperfine structure components of the 6s ^{2 1} S ₀6s6p ³P₁,λ=2,537 Å resonance line of the investigated isotope and the Hg lamp. The orientation built up by optical pumping is monitored via the asymmetry or anisotropy of the nuclear radiation. Nuclear spins, magnetic moments, electric quadrupole moments and the isotope shifts are obtained for¹⁸¹Hg-¹⁹¹Hg using theβ asymmetry as detector. The extension of the method using theγ anisotropy is discussed and test measurements on¹⁹³Hg are presented. This paper describes the experimental procedure, results, and discussion are given in a following publication.     

Laser spectroscopy of radioactive isotopes

The experimental conditions for laser spectroscopy of shortlived isotopes is discussed with respect to nuclear lifetime, reaction rates and samples preparation by on-line mass-separator techniques. The method of collinear laser spectroscopy is presented with results for medium mass elements near the closed proton shell Z=50. An interpretation of magnetic moments, spectroscopic quadrupole moments and the parabolic shape of the isotope shift in this region of nuclei is given.     

Laser photoionization spectroscopy of rare-earth elements: New results on nuclear electromagnetic moments and charge radii of Eu,Gd and Tb isotopes

New results on spins, electromagnetic moments and isotopic changes of nuclear charge radii for ₆₃ ^157–159 Eu, ₆₄ ^{146, 148, 150} Cd and ₆₅ ^{147–155, 157, 159} Tb have been obtained from hyperfine structure and isotope shifte measured with laser resonance photoionization technique. These results complement two-dimensional picture (with respect to H and Z) of the changes of nuclear ground state properties near the “critical” neutron numbers N=88–90 in the vicinity of the “magric” proten number Z=64.