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The 68m Cu/ 68 Cu isotope as a new probe for hyperfine studies: The nuclear moments
Abstract
Time Differential Perturbed Angular Correlation of γ-rays (TDPAC) experiments were performed for the first time in the decay of 68m Cu produced at the ISOLDE facility at CERN. Due to the short half-life of the source isotope, the measurements were carried out online. The intermediate state offers the unique opportunity to study the electromagnetic fields acting at a copper probe in condensed matter via hyperfine interactions. The present work allowed determination of the nuclear moments for this state. The electric quadrupole moment was obtained from an experiment performed in Cu2O and the magnetic dipole moment from measurements in cobalt and nickel foils. The results are discussed in the framework of shell model calculations and the additivity rule for nuclear moments with respect to the robustness of the N = 40 sub-shell.
... This includes all types of chemistry where implantation into easily dissolved substrates can be used to perform radiochemistry using 119 In or 57 Mn for eMS or 68 Cu for Perturbed Angular Correlation (PAC) measurements. 25 ...
An extension of the online implantation chamber used for emission Mössbauer Spectroscopy (eMS) at ISOLDE/CERN that allows for quick removal of samples for offline low temperature studies is briefly described. We demonstrate how online eMS data obtained during implantation at temperatures between 300 K and 650 K of short-lived parent isotopes combined with rapid cooling and offline eMS measurements during the decay of the parent isotope can give detailed information on the binding properties of the Mössbauer probe in the lattice. This approach has been applied to study the properties of Sn impurities in ZnO following implantation of ¹¹⁹In (T½ = 2.4 min). Sn in the 4+ and 2+ charge states is observed. Above T > 600 K, Sn²⁺ is observed and is ascribed to Sn on regular Zn sites, while Sn²⁺ detected at T < 600 K is due to Sn in local amorphous regions. A new annealing stage is reported at T ≈ 550 K, characterized by changes in the Sn⁴⁺ emission profile, and is attributed to the annihilation of close Frenkel pairs.
... Its characteristic properties were measured with the experiments in simple materials (Cu 2 O; Cu and Ni foils) used to determine the nuclear moments. [52] Cu 2 O was used to determine the nuclear quadrupole moment, using the obtained quadrupole constant, plus the ratio of quadrupole constants with respect to 65 Cu (obtained by NQR), and its ( 65 Cu) known quadrupole moment. ...
In this review we present examples of using radioactive isotopes as probes to study functional materials of fundamental and applied interest presenting colossal magnetoresistance, multiferroic effects, and magnetostructural coupling. Most of the works exploit the hyperfine properties, Electric Field Gradient (EFG) and Hyperfine Magnetic Field (HMF), of these probes through Perturbed Angular Correlation (PAC) spectroscopy. The measurements were complemented with density functional theory calculations to model the relevant properties and correlate the EFG with the electric polarization. We also present a methodological and nuclear physics related contribution consisting on the characterization of a new short lived isotope adequate for PAC studies. Finally, an ultra‐sensitive method to quantify the uptake of Hg by nanosorbents based on the tracking the radioactive isotopes of mercury is also reviewed. These works showcase the diversity of our research with radioisotopes, at the interface of different science fields, with combination of different methodologies and different motivations such as fundamental materials physics and chemistry or environmental concerns.
... The 5°deflector was installed in 2014, before the first online run at VITO, which used unpolarized 68m Cu for online perturbed 1, 0, 1 F D = -+ , after several excitation-decay cycles the lower state with m F F = + will be mostly populated and the atomic spin will be polarized. angular correlation studies [AF16]. The beam-diagnostics box installed behind it hosts a variable aperture and a metal plate from which the ion current can be read out. ...
Following a growing interest in spin-polarized beams of radioactive ions, a new laser spin-polarization setup has been installed at the ISOLDE facility at CERN. The setup is located at the VITO beamline which aims to bring together several experimental techniques using polarized ions allowing for studies in nuclear physics, fundamental interactions, material and life sciences. Intensive design work, which took place in 2016, allowed the installation of the first stage of the polarization line. With this experimental setup, the ion beam can be neutralized, polarized and implanted into a solid sample inside an electromagnet which also hosts β-detectors, where the degree of nuclear spin polarization can be measured. In autumn 2016 the setup was commissioned using short-lived ²⁶Na and ²⁸Na beams which were polarized in the D2 line from their atomic ground state. The previously observed degrees of β asymmetry were reproduced and thus the beamline is now ready for the first physics experiments with spin-polarized radioactive beams.
... At ISOLDE other interesting TDPAC isotopes, still not used in chemistry or biochemistry, have been characterized recently, such as the rare-earth 172 Lu/Yb (t 1/2 = 6.7 d) decaying by electron capture [20]. In 2014, a proof of principle using 68m Cu/Cu (t 1/2 = 3.75 m) isotope for TDPAC spectroscopy [17] was conducted, aiming towards new experiments in both solid state physics and chemistry. A c c e p t e d M a n u s c r i p t 8 We additionally wish to point to two interesting cases -still barely produced at ISOLDEbut currently produced by neutron activation at nuclear reactors that may deserve future investment in on-line production methods. ...
Time differential perturbed angular correlation (TDPAC) of γ-rays spectroscopy has been applied in chemistry and biochemistry for decades. Herein we aim to present a comprehensive review of chemical and biochemical applications of TDPAC spectroscopy conducted at ISOLDE over the past ~15 years, including elucidation of metal site structure and dynamics in proteins and model systems. β-NMR spectroscopy is well established in nuclear physics, solid state physics, and materials science, but only a limited number of applications in chemistry have appeared. Current endeavors at ISOLDE advancing applications of β-NMR towards chemistry and biochemistry are presented, including the first room temperature experiment on 31Mg in ionic liquid solution. Both techniques require the production of radioisotopes combined with advanced spectroscopic instrumentation present at ISOLDE.
... It is aimed to deliver beams of either spinpolarized or non-spin polarized atoms/ions to three fully independent experimental stations (operating from 10 −10 to 50 mbar): in addition to ASPIC, a β-asymmetry station and openend station suitable for traveling experiments. VITO opens up numerous new opportunities for multidisciplinary science in the areas of solid state physics, biophysics, nuclear physics and fundamental interactions (Ruiz et al 2015, Fenta et al 2016, Stachura et al 2016. ...
We review the research carried out using the apparatus for surface physics and interfaces (ASPIC), at ISOLDE, CERN. We give an overview of the research highlights since 2000, focusing on magnetic and non-magnetic metallic surfaces, and introduce the scientific program that will follow the upgrade which is currently underway, focusing on two-dimensional materials. ASPIC was formerly used for the growth of ultrathin metallic films and their characterization by means of perturbed angular correlation spectroscopy. Past research has mainly focused on the determination of the magnetic hyperfine field at the probe atom located on different sites at the surface such as terraces, kinks, steps as well as on the investigation of the static magnetic polarization at the interface between ferromagnetic and paramagnetic layers. Future research on two-dimensional materials using ASPIC is foreseen to focus on the investigation of structural and electronic properties of adatoms (adsorption sites, hybridization effects, intra-atomic charge transfer, magnetic moments, etc). We emphasize, in this context, the exceptional capabilities of ASPIC in terms of broad applicability, high precision and low detection limits.
The idea that “new-is-small” is a paradigm propelling industries and research: new materials for new applications and new technologies. Precise and efficient characterization techniques are, therefore, required to make the “new” and the “small”, understandable, applicable, and reliable. Within this concept, Time Differential Perturbed Angular Correlations, TDPAC, appears as one of the most exotic and efficient techniques to characterize materials and is celebrating 40 years at ISOLDE, CERN. In this overview we explore the TDPAC measurement possibilities at ISOLDE-CERN for solid state physics research with a rich potential due to the wide number of available radioactive probe elements, delivered with great purity and high yield.
Reports of room-temperature ferromagnetism continue to emerge for an ever-growing range of nanomaterials with a small or even vanishing concentration of magnetic atoms. Dilute magnetic semiconductors (DMS) are the most representative class of such materials, but similar magnetic properties have been reported in many others. Challenging our understanding of magnetic order in solids, as well as our ability to experimentally assess it, these remarkable magnetic phenomena have become one of the most controversial topics in magnetism. Various non-intrinsic sources of ferromagnetism (e.g. instrumental artifacts and magnetic contamination) are becoming well documented, and rarely are all of them taken into account when room-temperature ferromagnetism is reported. This topical review is intended to serve as a guide when evaluating to what extent a given data set supports the claim of intrinsic ferromagnetism in dilute nanomaterials. It compiles the most relevant sources of non-intrinsic ferromagnetism which have been reported, as well as guidelines for how to minimize them. It also provides an overview of complementary structural and magnetic characterization techniques which can be combined to provide different levels of scrutiny of the intrinsic nature of experimentally observed ferromagnetism. In particular, it gives some notable examples of how comprehensive studies based on those techniques have led to a remarkably detailed understanding of model DMS materials, with strong evidence of absence of room-temperature ferromagnetism. Although mostly based on DMS research, this review provides a set of guidelines and cautionary notes of broader relevance, including some emerging new fields of dilute nanomagnetism such as magnetically doped 3D topological insulators, 3D Dirac semimetals, and 2D materials.
Measurements of the ground-state nuclear spins and magnetic and quadrupole moments of the copper isotopes from 61Cu up to 75Cu are reported. The experiments were performed at the CERN online isotope mass separator (ISOLDE) facility, using the technique of collinear laser spectroscopy. The trend in the magnetic moments between the N=28 and N=50 shell closures is reasonably reproduced by large-scale shell-model calculations starting from a 56Ni core. The quadrupole moments reveal a strong polarization of the underlying Ni core when the neutron shell is opened, which is, however, strongly reduced at N=40 due to the parity change between the pf and g orbits. No enhanced core polarization is seen beyond N=40. Deviations between measured and calculated moments are attributed to the softness of the 56Ni core and weakening of the Z=28 and N=28 shell gaps.
The β decay of the neutron-rich 3081Zn51 has been investigated at the PARRNe mass separator at the IPN Orsay. The sources of 81Zn were produced using the ISOL (Isotopic Separation On Line) technique by the fission of natU exposed to the neutron flux produced by the 26-MeV deuteron beam delivered by the MP-Tandem. With γ and γ-γ coincidence measurements, excited levels were attributed to 3181Ga50 for the first time. A partial decay scheme for 81Zn is proposed. The proposed level scheme is well reproduced by shell model calculations using the most recent effective empirical interaction. We show that the structure of this nucleus is consistent with that of the heavier odd-proton N=50 isotones within the assumption of strong proton Z=28 and neutron N=50 effective shell effects. The observed states can be associated to rather simple and clean configurations of three protons placed in the 1f5/2 and 2p3/2 orbits.
One of the key issues in current nuclear physics research is to investigate the properties of so-called `exotic nuclei' and of `exotic nuclear structures'. Exotic nuclei are nuclei with a proton-to-neutron ratio that is very different from the proton-to-neutron ratio in stable nuclei (a technical term related to this ratio is the `isospin'). We define exotic nuclear structures as excitation modes of nuclei that have a very different structure than the structure (or shape) of the nuclear ground state. By putting the nucleons in a nucleus to extreme conditions of isospin and excitation energy one can investigate details of one of the four basic forces in nature:?the strong force which binds the nucleons together to form a bound nucleus. While the basic properties of the strong nucleon?nucleon interaction are known from investigating the properties of nuclei near the `valley of stability', recent developments in the study of exotic nuclei have demonstrated that specific properties of the strong interaction, such as the influence of the spin-orbit term, are not yet understood. Because the nucleus forms a complex many-body system, it is impossible to describe it by ab?initio calculations (except for a few very light nuclei, for which such calculations have become possible in the last few years) and therefore approximations need to be introduced. Several theoretical models have been developed in order to describe the properties of nuclei all over the nuclear chart. It is by measuring the basic nuclear properties such as masses, binding energies, lifetimes, excitation schemes, static and dynamic moments, and by comparing these properties to the predictions from the nuclear models, that these models can be tested and effective interactions can be improved. Furthermore, the measured nuclear properties can be a guide in understanding the changes, which the nuclear force undergoes in extreme conditions.
In this report, we focus on the electric and magnetic properties of a nuclear state, namely on what the static magnetic dipole and electric quadrupole moments can teach us about the nucleus as a system of independently moving particles in a central potential or as a system of collectively moving nucleons. We give an overview of some techniques to measure nuclear moments for a variety of nuclear states and we discuss how the recent developments in the production of exotic nuclei have influenced the development of new experimental tools for nuclear moment studies.
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.
The magnetic anisotropy of single-crystalline cobalt and the temperature dependence of the hyperfine fields of cadmium in cobalt were studied by the perturbed-angular-correlation technique without any applied magnetic field. A uniaxial basal-plane anisotropy was found instead of the expected threefold one, and was explained by lattice-deformation-induced anisotropy. The obtained temperature dependence of the angle between the magnetization and the c axis is in agreement with the uniaxial anisotropy constants K1 and K2 found by torque magnetometry. The room-temperature values of the hyperfine fields are Bhf=288(3) kG and VZZ=32(5)×1015 V/cm2.
The VITO (Versatile Ion-polarized Techniques Online) project is a new experimental setup at the ISOLDE facility at CERN. VITO is a dedicated beam line for producing laser-induced spin-polarized beams of both, atoms and ions, and it has been commissioned in response to the continuously growing demand for the use of spin-polarized beams. The new VITO beam line is a modification of the formerly existing ultra-high vacuum beam line, connecting ASPIC (Apparatus for Surface Physics and Interfaces at CERN), and it has been under construction since the beginning of 2014. Once fully commissioned, VITO will open up numerous possibilities for carrying out multidisciplinary experiments in the areas of nuclear and solid state physics, fundamental interaction physics and biophysics. In its final stage the VITO beam line will provide three fully independent experimental stations: UHV chamber for material science applications, a β-asymmetry station where highly-polarized ions will be available, and a central open-end station suitable for travelling experiments. The VITO beam line will operate in two different modes providing either beams of spin-polarized atoms or ions, or non-polarized ion beams to all three end stations operating from 10−10 mbar to 50 mbar. Recent experimental campaigns with stable and radioactive beams have allowed for testing VITO’s constituent parts and have demonstrated 96% of ion beam transmission to the collection chamber installed on the central station. The first experimental results obtained with on-line Perturbed Angular Correlation (PAC) spectroscopy using 68mCu ion-beams will be briefly discussed.
1. Introduction and Overview of Copper as an Element Essential for Life.- 2. Absorption of Copper from the Digestive Tract.- 3. Copper Uptake by Nongastrointestinal Vertebrate Cells.- 4. Extracellular Copper Substituents and Mammalian Copper Transport.- 5. Excretion of Copper in the Mammal.- 6. Copper within Vertebrate Cells.- 7. Copper and Metabolic Regulation.- 8. Copper in Growth and Development.- 9. Copper and Disease.- 10. Copper in Nonvertebrate Organisms.- Appendix A: Copper Contents of Foods.- Appendix B: Copper Content of Human and Animal Tissues.- References.
The multipole character and E2M1 mixing ratios of all γ
transitions following the decay of Ag110m to Cd110
have been determined by measuring the 1-2, 1-3, and 1-4 directional
correlations, using two 30-cc coaxial Ge(Li) detectors in conjunction
with a multichannel coincidence gating system. The analysis of the data
clearly demonstrated the necessity for careful investigations of the
effects of the Compton background on directional correlation
measurements using Ge(Li) detectors. The directional correlation
functions for mixed γ-γ cascades are given in terms of
explicitly defined reduced matrix elements and their ratios
δ(γn). The analysis of the 25 measured
directional correlations yielded a consistent set of E2M1 mixing ratios
for all mixed multipole transitions. The E2M1 amplitude ratios
δ(γn)=<In+1∥j-->NA-->E2∥In><In+1∥j-->NA-->M1∥IN>
for the Cd110 γ rays are (energies are in keV):
δ(447)=-0.45+/-0.20, δ(620)=-0.80+/-0.50,
δ(678)=-0.25+/-0.20,
δ(687)=-1.1+0.8-0.4,
δ(707)=-1.0+/-0.3, δ(818)=-1.20+/-0.15,
δ(1384)=-0.37+/-0.03, and δ(1505)=-0.55+/-0.10. In terms of
the multipole moments
<In+1∥M(πL)∥In> of Bohr and
Mottelson, the E2M1 moment ratios
Δ=<In+1∥M(E2)∥In><In+1∥M(M1)∥In>
in natural units (ℏ=m=c=1) are: Δ(447)=-3.0+/-1.3,
Δ(620)=-3.8+/-2.4, Δ(678)=-1.09+/-0.88,
Δ(687)=-4.7+3.4-1.7,
Δ(707)=-4.2+/-1.3, Δ(818)=-4.3+/-0.5,
Δ(1384)=-0.79+/-0.06, and Δ(1505)=-1.08+/-0.20.
In this review on target and ion sources for ISOL (Isotope Separation
OnLine) beams, important developments from the past five years are
highlighted. While at precedent EMIS conferences, a particular focus was
given to a single topics, for instance specifically on ion sources or on
chemical purification techniques, here each of the important elements
present in an ISOL production unit is discussed. Fast diffusing
nanomaterials, uranium-based targets, high power targets for next
generation facilities, purification by selective adsorption, new ion
sources are all part of this review. For each of these selected topics,
the reported results lead to significant gains in intensity, purity, or
quality of the delivered beam, or in the production of new isotope
beams. Often the outcome resulted from the combination of original ideas
with state-of-the-art investigations; this was carried out using very
different scientific disciplines, leading to understanding of the
underlying chemical or physical mechanisms at the origin of the
improvements.
The pure nuclear quadrupole resonance frequencies of 63Cu and 65Cu nuclei in Cu2O have been measured from 350 down to 4°K. Below 140°K the dependence deviates from linearity. A model based on vibrations of the Cu nuclei transverse to the O-Cu-O axis is shown to be consistent with the experiments. The frequency ω of the transverse vibrational band is derived to be 97±7 cm-1.
In a recent development of a fully digital spectrometer for time differential perturbed angular correlations a true constant fraction trigger (CFT) algorithm was implemented that, however, allowed for integer delays, i.e. integer multiples of the sampling interval, only. With a sampling rate of 1 GS/s and BaF2 scintillators this turned out to be insufficient. Here, we present an extension of the algorithm to fractional delays implemented in field programmable gate arrays (FPGAs). Furthermore, we derive a criterion for the delay for optimum timing based on the steepest slope of the CFT signal. Experimental data are given for LaBr3(Ce) scintillators and 511 keV–511 keV prompt coincidences that corroborate the theoretical result.
Recent progress in experimental techniques allows us to study very exotic systems like neutron-rich nuclei in the vicinity of Ni. The spectroscopy of this region can nowadays be studied theoretically in the large scale shell model calculations. In this work, we perform a shell model study of odd copper nuclei with N=40-50, in a large valence space with the Ca core, using a realistic interaction derived from the CD-Bonn potential. We present the crucial importance of the proton core excitations for the description of spectra and magnetic moments, which are for the first time correctly reproduced in theoretical calculations. Shell evolution from Ni to Ni is discussed in detail. A weakening of the Z=28 gap when approaching the N=50 shell closure, suggested by the experimental evidence, is confirmed in the calculations.
New shell model Hamiltonians are derived for the T=1 part of the residual interaction in the fââ pââ pââ gââ model space based on the analysis and fit of the available experimental data for âââµâ·Niââ-âââ·â¸Niââ isotopes and âââ·â·Cuââ-ââ¹°°Snââ isotones. The fit procedure, properties of the determined effective interaction as well as new results for valence-mirror symmetry and seniority isomers for nuclei near â·â¸Ni and ¹°°Sn are discussed.
63Cu and65Cu NMR studies are reported in liquid and solid copper (I) compounds. Ratios ofg
I-factors, nuclear magnetic moments and nuclear magnetic shielding constants in the atomic reference scale are given for63Cu and65Cu in a solution of Cu(I)(CH3CN)4BF4 in CH3CN, which is a reasonable reference sample due to the relatively narrow NMR line.
The lifetimes and the magnetic moments of the two excited62Cu states at 40.84 and 390.19 keV are investigated by time differential perturbed angular distribution measurements of the delayed?-rays following the nuclear reactions61Ni(d, n) and62Ni(p, n). The results are:t=6.7±0.5 nsec,µ=1.32±0.03 n. m. for the 2+ state at 40.84 keV, andt=16.0±0.3 nsec,µ=2.00±0.01 n. m. for the 3+ state at 390.19 keV.
Radioactive atoms produced in proton-induced nuclear reactions and
released from thick targets have been ionized resonantly by laser
radiation in a hot tube connected to the target container. Pulsed
tuneable lasers with a repetition rate as high as 10 kHz have been
applied for stepwise resonant excitation and photoionization in the last
step. In this way the efficiency and selectivity of the target and ion
source system which serves as an injector to the on-line isotope
separators at CERN-ISOLDE could be improved. In a series of off-line and
on-line studies the ionization of Sn (Ei = 7.3 eV), Tm
(Ei = 6.2 eV), Yb (Ei = 6.2 eV) and Li
(Ei = 5.4 eV) was investigated. An ionization efficiency of
up to 15% was obtained for Yb. The ratio of the laser-ionized and
surface-ionized ion currents was measured as a function of temperature
for different ionization cavity materials (W, Ta, Nb and TaC). It was
shown that this ratio, i.e. the selectivity, rises for Tm from 10 to
10000 with falling temperature and is strongly dependent on the
material. Since the lasers are pulsed the ion beam becomes bunched with
a pulse width of about 10-50 μs. This width is strongly dependent on
the potential drop along the tube (caused by the electric current used
for heating the tube) and on the alignment of the laser beams with
respect to the tube axis. The selectivity could be further improved by a
factor of 10 using gated detection of the bunched ion beam.
Copper(I) carbonyl complexes with a series of hindered LR1,R2 ligands (L: hydrotris(pyrazolyl)borate, R1 and R2 are substituents at the 3- and 5-positions of the pyrazole ring, respectively), LR1,R2CuCO [R1, R2 = Me, Me (1), i-Pr, i-Pr (2), t-Bu, Me (3), t-Bu, i-Pr (4), Ph, i-Pr (5), Ph, Ph (6)] have been synthesized and characterized by 1H NMR and IR spectroscopy and elemental analysis. The molecular structures of 3 and 6 have been determined by X-ray crystallography. The electronic structures of copper(I) sites are characterized by means of 63Cu NMR spectroscopy and by the CO stretching vibration. The sharp 63Cu NMR signals are observed for LR1,R2CuCO complexes in toluene at room temperature. The 63Cu NMR signals of copper(I) complexes with alkyl-substituted ligands (1−4) are observed in lower field than those of the phenyl derivatives (5, 6) correlating with the electron-density at the copper center. This argument is supported by the good correlation between the δ(63Cu) value and CO stretching vibration which is a sensitive indicator of the extent of back-donation of the Cu d electrons to the antibonding CO orbitals.
An advanced spectrometer for time differential perturbed γ-γ-angular correlation measurements is presented. It consists of six detectors with BaF2-scintillators and is designed to reduce the data collection time as much as possible. Experimental results with “illumination” times of the order of 100 s are presented. This “camera” storing 30 coincidence subgroups simultaneously is compared with a conventional four-detector system with eight subgroups.
A comperhensive study was made of the applicability of gamma‐ray angular correlations to the determination of quadrupole interactions in metals and insulating solids. Dynamic effects were studied in solutions and gases. A total of fourteen gamma‐ray cascades were employed. Several nuclear spins were confirmed and the quadrupole moments of ten excited nuclear states were determined or estimated from the data. Quadrupole coupling constants were determined for excited states of the following nuclei in metallic host lattices of the same element: 44Sc, 99Ru, 111Cd, 117In, 187Re, 199Hg. Coupling constants were also measured for the following isotope (lattice) combinations: 99Ru(Zn, Cd, Sn, Sb), 100Rh(Zn, Ru, Cu5Zn8, Pd2Al, PdPb2), 111Cd(In, Hg, Tl, CdSb, Cd3Ag, Zn, Ga, In, Sn, Sb, Bi, AuIn, InBi, In2Bi), 115In(Cd), 117In(Cd, Sn), 131I(Te), 181Ta(HfB2, HfSi2), 204Pb(Cd, In, Sn, As, Sb, Bi, Hg, Tl, PdPb2). Systematic variations of e 2 qQ with host‐lattice structure were observed and host and solute properties were found to be separable to some extent for nontransition metals. The nuclei 111Cd, 115In, 117In, 199Hg, and 204Pb were used to determine a total of fifty quadrupole coupling constants in insulators, including twenty with nonzero asymmetry parameters, which give oscillatory but aperiodic correlation functions. It was strikingly (and exhaustively) demonstrated that good determinations of quadrupole coupling constants could be made following isomeric transitions (IT) (with no elemental transmutation) and beta decay (with elemental transmutation). However, in no case was it possible to derive a coupling constant from a gamma‐ray cascade preceded directly by electron‐capture (EC) decay, presumably because the sudden creation of a K‐hole, and the Auger and ``shake‐off'' events that follow, destroy the chemical integrity of the species under study. Relaxation times were determined for a number of liquid samples. Studies of dimethyl‐111mCd in various buffer gases showed that the spin memory was lost in one collision with heavy molecules, but that light molecules required several collisions.
Analytic expressions are presented for powder and single crystal perturbation functions in ®–®-angular correlations for static
interactions. Magnetic dipole interactions for arbitrary spin as well as non-axially symmetric electric quadrupole interactions
up to spin 5/2 are treated. Symmetry properties of all matrices involved are discussed, as well as their consequences for
the perturbation functions. A new complementarity rule for powder perturbation functions is presented.
A user-friendly fully digital TDPAC-spectrometer with six detectors and fast digitizers using Field Programmable Gate Arrays
is described and performance data are given.
KeywordsUser-friendly–Digital TDPAC-spectrometer–Field programmable gate arrays
The internal fields H
i
in ferromagnetic alloys were measured at both the solvent and the solute nuclei at magnetic and nonmagnetic atoms using NMR techniques. Co59 resonances in Co-rich alloys (Co-Fe, -Ni, -Cu, -Cr, -Mn, -Al) have fine structures which depend on the kind and the concentration of impurity metals. Similar structures are found for the Fe57 resonances in Fe-rich alloys. These structures are tentatively interpreted as caused by the anisotropy of H
i
at the nearest neighbors. The Co59 resonance is also observed in Fe-rich Co-Fe alloys, and it is found that H
i
seen at the Co site is lower by about 50 koe than that at the Fe site. The Co59 line width is about 400 kc for (Fe+1% Co) alloy. Both the temperature and the pressure dependences of the Co59 frequency were measured. H
i
at Cu63 and Cu65 was measured in Co-rich Co-Cu and in Fe-rich Fe-Cu ferromagnetic alloys. The magnitude of these internal fields at Cu and their observed pressure dependence are, at least, not inconsistent with the contention that the observed H
i
is mainly produced by the 4s conduction-electron polarization, although H
i
at the Cu nucleus, 217.7 koe for Fe-Cu alloy and 157.5 koe for Co-Cu alloy, is considerably higher than the usual theoretical prediction.
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A user-friendly fully digital time differential perturbed angular correlation (TDPAC)-spectrometer with six detectors and fast digitizers using field programmable gate arrays (FPGA) is described and performance data are given. The new spectrometer has an online data analysis feature, a compact size, and a time resolution such as conventional analog spectrometers. Its calculation intensive part was implemented inside the digitizer. This gives the possibility to change parameters (energy windows, constant fraction trigger delay) and see their influence immediately in the γ-γ correlation diagrams. Tests were performed which showed that the time resolution using a (60)Co source with energy window set at 1.17 MeV and 1.33 MeV is 265 ps with LaBr(3)(Ce) scintillators and 254 ps with BaF(2) scintillators. A true constant fraction algorithm turned out to be slightly better than the constant fraction of amplitude method. The spectrometer performance was tested with a TDPAC measurement using a (44)Ti in rutile source and a positron lifetime measurement using (22)Na. The maximum possible data rate of the spectrometer is 1.1 × 10(6) γ quanta per detector and second.
(65)Cu central-transition NMR spectroscopy of the blue copper protein azurin in the reduced Cu(I) state, conducted at 18.8 T and 10 K, gave a strongly second order quadrupole perturbed spectrum, which yielded a (65)Cu quadrupole coupling constant of +/-71.2 +/- 1 MHz, corresponding to an electric field gradient of +/-1.49 atomic units at the copper site, and an asymmetry parameter of approximately 0.2. Quantum chemical calculations employing second order Møller-Plesset perturbation theory and large basis sets successfully reproduced these experimental results. Sensitivity and relaxation times were quite favorable, suggesting that NMR may be a useful probe of the electronic state of copper sites in proteins.
The principal focus of this study is the (63)Cu NMR line widths in Cu(I)-acetonitrile (AN) solutions. The variations with the concentrations of Cu(I) salts (trifluoromethanesulfonate and perchlorate), added salts, water, chloride ion, and temperature have been studied. A quantitative analysis shows that the anomalous temperature dependence of the line widths is not due to ion pairing or anion complexation but results primarily from formation of a species with a different coordination number or less symmetrical arrangement of AN ligands than in the normal tetrahedral Cu(AN)(4)(+) ion. Solvent viscosity and ion pairing (with triflate) also are identified as factors having the expected effects on the line widths. The results of earlier studies also are discussed and analyzed by the current model where possible.
The electron-transfer kinetics for each of three copper(II/I) tripodal ligand complexes reacting with multiple reducing and oxidizing counter reagents have been examined in aqueous solution at 25 degrees C, mu = 0.10 M. For all of the ligands studied, an amine nitrogen serves as the bridgehead atom. Two of the ligands (PMMEA and PEMEA) contain two thioether sulfurs and one pyridyl nitrogen as donor atoms on the appended legs while the third ligand (BPEMEA) has two pyridyl nitrogens and one thioether sulfur. Very limited kinetic studies were also conducted on two additional closely related tripodal ligand complexes. The results are compared to our previous kinetic study on a Cu(II/I) system involving a tripodal ligand (TMMEA) with thioether sulfur donor atoms on all three legs. In all systems, the Cu(II/I) electron self-exchange rate constants (k(11)) are surprisingly small, ranging approximately 0.03-50 M(-)(1) s(-)(1). The results are consistent with earlier studies reported by Yandell involving the reduction of Cu(II) complexes with four similar tripodal ligand systems, and it is concluded that the dominant reaction pathway involves a metastable Cu(II)L intermediate species (designated as pathway B). Since crystal structures suggest that the ligand reorganization accompanying electron transfer is relatively small compared to our earlier studies on macrocyclic ligand complexes of Cu(II/I), it is unclear why the k(11) values for the tripodal ligand systems are of such small magnitude.
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