Measurements Of Nuclear Moments Research Articles

Tin resonance-ionization schemes for atomic- and nuclear-structure studies

This paper presents high-precision spectroscopic measurements of atomic tin using five different resonance-ionization schemes performed with the collinear resonance-ionization spectroscopy technique. Isotope shifts were measured for the stable tin isotopes from the $5{s}^{2}5{p}^{2}\phantom{\rule{0.28em}{0ex}}^{3}{P}_{0,1,2}$ and ${}^{1}{S}_{0}$ to the $5{s}^{2}5p6s\phantom{\rule{0.28em}{0ex}}^{1}{P}_{1},^{3}{P}_{1,2}$ and $5{s}^{2}5p7s{\phantom{\rule{0.28em}{0ex}}}^{1}{P}_{1}$ atomic levels. The magnetic dipole hyperfine constants ${A}_{\mathrm{hf}}$ have been extracted for six atomic levels with electron angular momentum $Jg0$ from the hyperfine structures of nuclear spin $I=1/2$ tin isotopes, $^{115,117,119}\mathrm{Sn}$. State-of-the-art atomic calculations using a relativistic Fock-space coupled-cluster method and the configuration interaction approach combined with many-body perturbation theory allow accurate and reliable calculations of both field- and mass-shift factors for the studied transitions, in addition to the hyperfine magnetic fields and electric-field gradients of the atomic levels. The excellent agreement with the experimental results highlights the accuracy of modern atomic theory and establishes an important foundation for precision measurements of nuclear moments and charge radii of the most exotic isotopes of tin.

Ground state moments and spins of neutron-rich K and Al isotopes as probes for changes in nuclear structure

This contribution focusses on recent measurements of nuclear moments and spins using two complementary methods. The ground state magnetic moments and spins of the exotic isotopes 49,51K have been measured at the ISOLDE facility at CERN using bunched-beam high-resolution collinear laser spectroscopy. The re-inversion of the ground state spin from I = 1/2 in 47,49K back to the normal I = 3/2 in 51K has been established. At GANIL (Caen, France) the quadrupole moment of the 33Al ground state has been measured using the continuous-beam β-nuclear magnetic resonance method applied to a spin-polarized beam produced at the LISE fragment separator. The large value establishes a very mixed wave function with about equal amounts of normal and neutron particle-hole excited configurations contributing to its ground state wave function. This illustrates the transitional nature of isotopes at the border of the island-of-inversion.

Polarized Radioactive Beams and Nuclear Moment Measurements for Exotic Nuclei

Viewing a nucleus as a collection of independent particles has been, since the spin-orbit force was introduced [1], a successful way of understanding major nuclear properties that are governed by a particular series of numbers—the magic numbers. Such properties result from the bunching of the single-particle orbits, or the existence of nuclear shells. About half a century after, however, the present-day studies of nuclei far from the β stability line reveal that the nuclear shells may evolve [2]: As the N/Z ratio increases, the single particle orbits migrate upward or downward in energy depending on their j = l ± 1/2 character. As a result the decisive role played by one orbit (the valence orbit) is taken over by another, and in some cases the nuclear deformation sets in even in a nucleus whose N or Z number is a (heretofore) magic number. In such a situation, the nuclear moments, namely the magnetic dipole moments μ and electric quadrupole moments Q, serve as very useful indicators for alterations in nuclear structure.

Study of electromagnetic moments in unstable nuclei with radioactive nuclear beams

The measurements of nuclear moments have been conducted at RIKEN for the study of nuclei far from the β stability. Recent results for the magnetic moments of 30Al and 32Al obtained by means of β-NMR spectroscopy with spin-polarized radioactive beams from the projectile fragmentation reaction are presented. Remarks are also made on the developments and prospects for future moment studies at the RI Beam Factory.

Measurement of nuclear moments in the region of light neutron-rich nuclei

Measurement of nuclear moments in the region of light neutron-rich nuclei

Static Moments of Neutron-Rich Ground States and Isomers Produced by Projectile Fragmentation

New achievements in nuclear moment measurements on nuclei produced and spin-oriented in intermediate energy (50–80 MeV/u) projectile fragmentation reactions are presented. By combining different types of spin-orientation with different experimental techniques, we show that the magnetic dipole moments and electric quadrupole moments of exotic neutron rich nuclei in their ground state as well as in their excited isomeric states can be measured. A selection of recent experiments performed at the LISE spectrometer at GANIL (Caen, France) is described.

Measurement of nuclear moments and radii by collinear laser spectroscopy and by β-NMR spectroscopy

Experiments using laser spectroscopy and nuclear magnetic resonance techniques have been performed at ISOLDE on the unstable isotopes of several light elements. The results include nuclear ground state spins, magnetic dipole and electric quadrupole moments, and the behaviour of mean square nuclear charge radii within isotopic strings. These give important information about the nuclear structure at shell closures and close to the drip lines.

Isomer separation and measurement of nuclear moments with the ISOLDE RILIS

Short-lived radioisotopes are element selectively ionized by the resonance ionization laser ion source (RILIS) of the on-line isotope separator ISOLDE (CERN). The relative production of low and high spin isomers can be significantly changed when a narrow-bandwidth laser is used to scan through the atomic hyperfine structure. This allows the assignment of gamma ray transitions to the decay of the individual isomers. Moreover, the measurement of the hyperfine splitting provides a very sensitive method for the determination of magnetic moments of exotic isotopes. The technical developments are discussed for the example of copper.

Molecular beam measurements of nuclear moments before magnetic resonance. Part I: I. I. Rabi and deflecting magnets to 1938

Summary Investigation of the origin and function of three magnets from I. I. Rabi's laboratory at Columbia University leads to a closer inquiry into the early history of molecular beam evaluations of the angular momenta and magnetic moments of atomic nuclei than has been undertaken heretofore. The resulting insights into the background and the course of Rabi's research programme would probably not have occurred without the orientation enforced by these artifacts.

Startup of the Fragment Mass Analyzer at ATLAS

The Fragment Mass Analyzer (FMA) is currently being brought into operation at the Argonne Tandem Linear Accelerator System (ATLAS). The FMA is a recoil mass spectrometer, 8 m in length, which will be used to separate nuclear reaction products from the primary beam and disperse them by mass/charge ( m/ q) at the focal plane. It has a solid angle of 8 msr, an energy acceptance of ±20% around the central energy, and an m/ q acceptance of ±7% around the central mass. The FMA will allow the study of gamma rays originating from weak fusion-reaction channels by gating the gamma spectra by the desired ion identified at the FMA focal plane. Production and decay of nuclei far from stability will be studied at the FMA focal plane by implanting exotic recoils directly into detectors or by using a fast tape system to transport the recoils to shielded detector systems. With its capability of rotating from −5 to + 45° around the target, the FMA wil also be used for reaction mechanism studies. Beta-NMR and nuclear moment measurements will be made behind the focal plane. A facility description and a progress report on the commissioning of the FMA are presented.

Drastic enhancement of nuclear magnetic resonance in a hcp cobalt single crystal magnetized perpendicular to the c axis.

Nuclear magnetic resonance on oriented nuclei was performed for the first time using as host matrix a hexagonal Co single crystal magnetized perpendicular to the c axis. The radioactive isotope $^{191}\mathrm{Pt}$ was implanted using the mass-separator ISOLDE-3 at CERN. In comparison to the case of magnetization parallel to the c axis, a drastic enhancement of the resonance signal was observed. This observation opens new possibilities for precise measurements of nuclear moments of short-lived isotopes far from stability.

The argonne fragment mass analyzer

The fragment mass analyzer (FMA) is currently under construction at the ATLAS facility. The FMA is an 8 m long recoil mass spectrometer which will be used to separate nuclear reaction products from the primary heavy-ion beam and disperse them by M/ q (mass/charge) at the focal plane. The FMA will be used in many different types of experiments. Gamma rays originating from very weak fusion-evaporation channels can be observed in coincidence with the recoil nucleus identified at the FMA focal plane. Production and decay of nuclei far from stability will be studied at the focal plane by implanting exotic recoils directly into detectors or by using a fast tape transport system. The FMA will also be used for reaction mechanism studies. A radioactive beam facility behind the focal plane is planned, which will allow beta-NMR and nuclear moment measurements to be made. The FMA will utilize the wide range of beams and intensities to be provided by the new electron cyclotron resonance (ECR) source and positive ion injector, also under construction at ATLAS.

In-beam measurements of nuclear moments

Nuclear moments contribute valuable information to nuclear structure studies of nuclei under extreme conditions, such as nuclei at high angular momentum or far from stability. While the magnetic moment is sensitive to the nature of the participating nucleons (neutron or proton) the quadrupole moment is a direct measure for nuclear deformation.

Nuclear magnetic resonance of 9Be atoms by charge exchange with optically pumped 9Be+ ions

Abstract NMR of free 9 Be (I = 3 2 ) 1 S 0 atoms is observed via resonant charge exchange with optically pumped 9 Be + 2 S 1 2 ions in He buffer gas, yielding μ( 9 Be ) = −1.1778 (9) μ n . Applications of the method suitable for all group II elements and Yb include: precision measurements of nuclear moments, chemical shifts, hfs-anomalies, and investigation of charge exchange processes.

New Methods and Results in Nuclear Moment Measurements Reported at the Uppsala Conference (June 10-14, 1974)

A summary of the measurements of magnetic dipole moments and electric quadrupole moments of nuclear states reported at the Uppsala Conference on Hyperfine Interactions (June 10-14, 1974) is given (in table form) The various methods employed for the measurements of nuclear moments (mostly of excited states) are reviewed, emphasizing the advantages and disadvantages of each. Possible future developments in nuclear moment measurements are discussed.

Technique for Precision Measurements of Nuclear Moments in Free Atomic Ions

Technique for Precision Measurements of Nuclear Moments in Free Atomic Ions

Nuclear Moments and Intermediate Coupling

The effect of intermediate coupling on the calculation of the nuclear moments of the rare earths from analyses of hyperfine structure is examined. It is shown that the observed hyperfine splittings may be satisfactorily interpreted as due to the interaction of the spin and orbital moments of 4f electrons with the nuclear magnetic and electric quadrupole moments. The interaction of the electron-spin moments with the nuclear magnetic moment is shown to be very sensitive to the form of the coupling. The consistency of the measurements of nuclear moments by atomic-beam and paramagnetic resonances is discussed. Instead of using the more usual spin-Hamiltonian formalism, the matrix elements of the interactions are calculated explicitly in terms of the actual quantum numbers of the states involved. Calculations are presented for Pr141 and Ho165.

The Time Average Magnetic Field at the Nucleus in Nuclear Magnetic Resonance Experiments

For the high precision measurement of a nuclear gyromagnetic ratio by the Purcell or Bloch resonance methods, accurate knowledge of the time average magnetic field ${H}_{\mathrm{Av}}$ at the positions of the nuclei is necessary. The various component fields contributing to ${H}_{\mathrm{Av}}$ are listed. An experimental study is made of two of these fields: the magnetic shielding field in molecules and the magnetization field of paramagnetic ions added to a sample. In an earlier paper accurate computed values were given of the magnetic shielding field for free atoms and monatomic ions. The effect of these fields on the attainable precision in the measurement of nuclear moments is discussed.

Magnetic shielding of nuclei in molecules

An expression is developed for the magnetic field at a nucleus of a poly-atomic molecule with zero resultant orbital and spin angular momenta in an external magnetic field. The field at the nucleus is not the same as the externally applied field because of the field arising from the motion of the electrons in the molecule. The expression for the electron contribution to the magnetic field is shown to consist of two parts. The first is a simple term that is similar to the diamagnetic correction developed by Lamb for atoms. The second is a complicated one arising from second order paramagnetism and is analogous to the term dependent on the high frequency matrix elements in the theory of molecular diamagnetism. Under certain circumstances the second order paramagnetism term could become quite large. Since both of these terms are altered when the same nucleus is in different molecules, they at least partially and perhaps completely explain the chemical effect in nuclear moment measurements that has been reported by various observers. For linear molecules, the second order paramagnetism term is shown to be directly related to the experimentally measurable spin-rotational magnetic interaction constant of the molecule. This relation is particularly valuable in the important case of molecular hydrogen where it is shown that the correction for second order paramagnetism is −0.56 × 10 −5. When this is added to the Lamb type term as calculated by Anderson, the total magnetic shielding constant for molecular H 2 becomes 2.68 × 10 −5

Measurement of Nuclear Moments by Nuclear Magnetic Resonance Absorption

Measurement of Nuclear Moments by Nuclear Magnetic Resonance Absorption