Angular Correlation Studies Research Articles

Ion beam channeling and hyperfine interaction analysis for the characterization of stoichiometry and anti-site population in LiNbO 3

Combined high precision RBS/channeling, NRA/channeling and perturbed angular correlation studies were used to characterize near-stoichiometric and congruent LiNbO 3 crystals. In congruent LiNbO 3 two non-equivalent Li sites are distinguished whereas in near-stoichiometric LiNbO 3 only one of them exists. A comparison of the experimental results with Monte Carlo simulations was performed to check the validity of the different models for the structure of congruent lithium niobate crystals.

Perturbed angular correlation studies of structure and dynamics in biomolecules

Perturbed angular correlation studies of structure and dynamics in biomolecules

Perturbed Angular Correlation Study of Impurities Interaction in Si

Perturbed Angular Correlation Study of Impurities Interaction in Si

A normalization procedure for the four-detector system in γ-γ angular correlation studies

A normalization procedure for the four-detector system in γ-γ angular correlation studies

Time-differential perturbed angular correlation studies of in-complexes used in nuclear medicine

For determination of the stability of In3+ complexes with diethylenetriaminepentaacetic acid (DTPA) and newly synthesized chelates-derivatives of 4-amino-2-hydroxybutyric acid in aqueous solutions of pH 1.0–7.5, at room temperature, the time differential perturbed angular γ−γ correlation method was used. Data obtained show that only one of the new ligands forms as strong a complex as DTPA and can be used in water at pH∼7.

Electric field gradient and its temperature variation at a 181Ta probe in Zr2Fe and Zr2Co intermetallic compounds

In this paper we report a time differential perturbed angular correlation study of electric field gradients and their temperature variation in Zr2T (T = Fe,Co) intermetallic compounds (C16 crystallographic structure). Measurements were performed at a 181Ta radioactive probe in the temperature range 20 K–1173 K. In both samples only one strong asymmetric quadrupole interaction was observed, consistently with one possible crystallographic position of the probe atom in the studied structure. The quadrupole coupling constant is equal to 1039(8) MHz with asymmetry parameter η = 0.82 and 889(7) MHz with η = 1 at room temperature for Zr2Fe and Zr2Co respectively. In the investigated temperature range a linear dependence of electric field gradient was observed in contrast to the T32 dependence found in most intermetallic compounds and non-cubic metals.

Perturbed angular correlation (PAC) study of magnetic/(non)-magnetic multilayers

Abstract Using ion implanted Fe Cr , Co Ag and Fe Co multilayers we demonstrate our sensitivity to identify the different Co-phases as a function of growing conditions. The metastable bcc-Co phase is identified, while the Cr layers are strained bcc, but lose the Cr-bulk magnetism for thickness below 50 A.

Perturbed angular correlation study of the pseudo-binary system U(In 1− xSn x) 3

Microscopic information on the magnetic state in U(In 1− x Sn x ) 3 is obtained by perturbed angular correlation (PAC) spectroscopy. For temperatures above the magnetic ordering, the electric quadrupole hyperfine interaction strength follows a linear temperature dependence, while the magnitude reveals a reduced electronic enhancement. In the pseudo-binary compounds we conclude that the valence difference between In and Sn is small. The low temperature PAC spectra for the indium-rich compounds are understood in terms of a two-sites model with temperature dependent relative populations but confirm the triple- k anti-ferromagnetic ordering suggested earlier to reconcile Mössbauer and neutron scattering data. For the pure UIn 3 case, however, a spin reorientation is observed.

Positron Annihilation and Perturbed Angular Correlation Studies of Defects in Neutron and Heavy Ion Irradiated Si

Positron Annihilation and Perturbed Angular Correlation Studies of Defects in Neutron and Heavy Ion Irradiated Si

A perturbed angular-correlation study of the electric-field gradient at the In site in compounds of the Hg-In alloy system

The electric-field gradient (EFG) of dilute 111Cd nuclei in compounds of the Hg-In alloy system has been investigated by perturbed angular correlation (PAC) measurements of the electric quadrupole interaction (QI) of 111Cd on In sites. It has been found that, as in the pure metals Hg and In, the quadrupole frequency decreases with increasing temperature according to the relation nu q(T)= nu q(0)(1-BT32/). The strength constant B in the intermetallic phases, however, is up to 35% smaller than in the pure metals. The QI parameters are consistent with an orthorhombic gamma -Pu-type lattice for beta -Hg (Hg80In20), but are difficult to reconcile with the structures proposed for HgIn. An intermetallic compound HgIn2 has not been observed.

Angular correlation studies of positron annihilation in the noble gases

Two-dimensional angular correlation distributions have been measured for the first time for positron and positronium annihilation in low-density helium, neon, argon, krypton and xenon, and in a range of helium-xenon mixtures. The full widths of the (cylindrically averaged) free positron components are in reasonable agreement with theoretical values. The intensity of the mixed-state positronium (Ps) component (mean vacuum lifetime 9.7 ns in a magnetic field of 0.8 T) in helium is consistent with the Ps fraction previously determined in lifetime measurements; the widths of the Ps component in helium, neon and argon are consistent with a Ps-atom scattering cross section below 6.8 eV in all three gases of approximately (9-0.5 E) pi a02, where E is the Ps energy in eV.

Heavy metal coordination chemistry in mercaptides and enzymes studied by TDPAC

Time differential perturbed angular correlation (TDPAC) studies of the coordination chemistry of the heavy metal atoms Cd and Hg via the nuclear quadrupole interaction are presented for the following systems; (i) mercury complexes with mercaptides, polymers with thiol groups, and ferrocenethiols. Mercury has a strong tendency to form linear or almost linear bonds with sulfur ligands. Evidence for 1,3-dithia-2-mercura[3]ferrocenophane formation is presented. (ii)111mCd-derivatives of the small electron transport proteins azurin, including a his 117gly mutant, and stellacyanin. The titration of the his 117gly mutant of azurin with imidazole was monitored in situ. (iii)111mCd- and199mHg-derivatives of the multi-Cu enzymes ascorbate oxidase and laccase. Reconstitution probabilities for Hg-reconstitution will be given as well as information on selective depletion and blocking of Cu-sites.

Search for positron localization near transition-metal solutes of negative effective charge in Ni and Cu

Results of an early (1973) angular correlation (ACAR) study of dilute (0.5% at.%) Cu based alloys by a Japanese group were interpreted in terms of an attraction of e + by transition metal solutes of effective negative charge. Doppler Broadening (DB) measurements reveal no such an effect for Cu(Mn) and Cu(Ni) solid solutions as well as for Ni alloys with 3d, 4d and 5d transition metal solutes (0.1 to 1.5 at.%) i.e. no evidence of e + localization near these impurities is seen. Our results strongly suggest that the ACAR results are due to the metallurgical state of the samples. In contrast, significant DB lineshape parameter variations, observed for our Ni(Zr) alloys, are attributed to positron trapping in and near Ni 5 Zr precipitates. Our DB results for a series of Ni(Au) alloys are understood in terms of a combination of the effect of an overall lattice expansion and a positron preference for clusters of Au atoms. The above comparison between DB and ACAR results is supported by our «spin polarized» DB results for a (001) Ni single crystal which resemble those obtained by other groups using a «spin polarized» 2D-ACAR technique

Perturbed angular correlation studies of the metal-binding sites in ovotransferrin and its C- and N-terminal halves

The perturbed angular correlation (PAC) technique has been applied to study the electric quadrupole interaction of 181Hf nuclei at the binding sites of ovotransferrin (OTF) molecules. Two specific electric field gradients were observed. Their relative intensities depend on the pH value and the temperature of the samples, whereas the electric quadrupole interaction parameters themselves remain unaffected. In order to compare the binding sites in OTF, experiments with N- and C-terminal half-molecules were performed. Both specific configurations are observed at the N-terminal and at the C-terminal binding site with similar quadrupole parameters as for the intact protein. Remarkably, the stability of the hafnium binding to the C-terminal fragment appears to be reduced as compared with the N-terminal half and the intact protein.

Time differential perturbed angular correlation study of impurity distribution in dilute [formula omitted] and [formula omitted] alloys

Impurity interactions in dilute ternary alloys NiFe(In) and NiPd(In) were studied by the time differential perturbed angular correlation method. A strong InPd attraction and a weak InFe repulsion were determined in a nickel host. The In/Cd probe sensed magnetic hyperfine field shifts caused by Fe impurities in three nearest neighbour shells around the probe, while no magnetic-moment perturbation was found due to Pd impurity atoms in a nickel host.

Perturbed angular correlation study using147Nd as a probe

The time integral pertturbed angular correlation (TIPAC) technique is employed to study PAC parameters in aqueous solutions of biomolecules Bovine Serum Albumin (BSA), lysozyme and ethylenediaminetetraacetic acid disodium salt (EDTA), using radioactive147Nd as a probe. The attenuation coefficient (G22) is found to decrease with increasing concentration of BSA The effect of attenuation is more pronounced for protein molecules BSA and lysozyme than in the case of EDTA. The relaxation constant (λ2) increases with increasing concentration of the solution as well as with the increasing size of the solute molecule.

Production of 77Br for TDPAC studies

An inexpensive target system for the production and on-line extraction of no carrier-added radioisotopes of bromine is described. The suitability of 77Br as a probe for time-differential perturbed angular correlation studies is discussed.

Impurity trapping in the Laves phase HfV2 detected by perturbed angular correlations

A perturbed gamma gamma angular correlation (PAC) study of the electric quadrupole interaction (QI) of 111Cd probes on substitutional V sites in the C15 Laves phase HfV2 has revealed a pronounced thermal hysteresis of the QI and the 111Cd fraction on regular V sites: when samples are cycled through 700 K in vacuum, the quadrupole frequency nu Q on the way down is found to be systematically larger than that on the way up at the same temperature. Simultaneously a sharp irreversible drop of the regular site fraction occurs upon cooling from 700 K. This behaviour indicates that HfV2 reacts with water vapour at T<or=700 K, dissociating residual H2O into its atomic components. HfV2 acts as a strong getter for the hydrogen, which is absorbed upon cooling below 700 K and again desorbed at T>800 K. The oxygen, however, is absorbed only in trace amounts. These conclusions are supported by a mass spectroscopic desorption measurement and a comparative PAC study of QI in the hydride HfV2H0.1, for which the activation energy for the hydrogen diffusion has been determined to be Ea=0.070(25) eV.

Spatial antibunching of photons

We study the angular correlations of photons emitted spontaneously by a set of sources placed at fixed positions with the use of a model of harmonic oscillators coupled to the electromagnetic field. In our previous study of angular correlations, in which the oscillators were treated as one dimensional and their Coulomb interactions were disregarded, we found only positive angular correlations over the whole range of interatomic separations for which the model was applicable. In this paper we use the model of three-dimensional oscillators interacting with the quantized electromagnetic field and also directly among themselves via the Coulomb forces. We solve this model analytically in the dipole approximation, and we calculate the angular correlation coefficient for different separations between the emitters. For separations less than half of the wavelength, we find negative angular correlations (spatial antibunching). This is a purely quantum effect that is not present in the corresponding classical stochastic model.

A study of angular correlations in 4-jet final states of hadronicZ 0 decays

Four-jet final states of hadronicZ 0 decays, observed ine + e − annihilation around 91 GeV centre of mass energy, are analysed in terms of observables that are sensitive to the non-abelian gauge structure of QCD. After correction for detector resolution and fragmentation effects, the data are compared to QCD and also to predictions of the Abelian vector gluon gauge theory. The theoretical expectations are calculated in both second order and leading logarithmic approximation of perturbation theory. The data are compatible with QCD but cannot be described by the predictions of the Abelian vector gluon models. From the measured topological distributions, upper limits for the relative production rates of\(q\bar qq\bar q\) final states are derived.