Investigation of statistically perturbed angular correlations of154Gd and156Gd in different liquid sources

The statistical perturbations of γγ-angular correlations involving the first 2⁺ rotational state of¹⁵⁴Gd and¹⁵⁶Gd have been time differentially investigated. We used liquid sources of 3⁺ ions of Gadolinium in lN perchloric acid, 0.5 N and 1N hydrochloric acid, 1.3N and 2.6 N sulfuric acid. Influences of the various chemical surroundings on the ratio λ₄/λ₂ of the attenuation parameters have been found. A simultaneous measurement of the angular correlation of the 874 keV–123 keV cascade and the 2,098 keV–89 keV cascade of¹⁵⁴Gd and¹⁵⁶Gd, respectively, has been performed in perchloric solution. From the ratio of the attenuation parameters λ₂, obtained by this experiment, we have derived the ratio of the magneticg-factors of the first 2⁺ levels of these isotopes asg ¹⁵⁴/g ¹⁵⁶=1.11±0.08.     

Time differential perturbed angular correlation studies with154Gd in a liquid environment at different temperatures

The perturbation of gamma-gamma angular correlations in the 1.17 ns 2+ state of¹⁵⁴Gd has been studied by using the¹⁵⁴Eu activity dissolved in 6N HClO₄. Time differential measurements were performed at five different temperatures between 0 °C and ?80 °C. The environment remains in the liquid phase in the whole temperature range and the attenuation of the angular correlations can be described by the theory of Abragam and Pound⁵. The observed attenuation parameters λ₂ and λ₄ were used to derive separately the strengths of the magnetic dipole interaction and the electric quadrupole interaction between the nuclei and their environment. The observed temperature dependence of the magnetic dipole and electric quadrupole interaction strength can be understood by a simple model of the attenuation mechanism.     

Time differential perturbed angular correlation studies of hafnium hydrides

The dependence of the electric field gradients (EFG) in Hafnium-Hydride systems as a function of the composition H/Hf in the cubic δ and tetragonal ε phases were investigated using the time-dependent perturbed angular correlation (TDPAC) technique, with¹⁸¹Ta as the nuclear probe. Two EFGs were found in the ε phase, indicating the existence of two major symmetries surrounding the Ta probe. The results indicate that the trend of the EFGs, in the ε phase, are due to the changes in the lattice parametersa _o,c _o as hydrogen is added to the Hf-H system. In the δ phase, only one major symmetry was found. Both phases are characterized by broad frequency distributions and large anisotropies.     

Interpretation of perturbed angular distribution results for19F implanted into diamond

Perturbed Angular Distribution measurements have been made on natural diamond using recoil implanted fluorine ions as probes. Two distinct lattice sites for fluorine in diamond were found. Site identifications prompted by theoretical cluster calculations are presented. The PAD data are well described by a texture theory, though the origin of the texture effects is presently not known.     

Coulomb correlations and shapes of XPS spectra of ferromagnetic Fe−Ni alloys

Summary The effect of the Coulomb correlations in partially filled valenced-bands has been considered by computing the renormalized valence band spectra for alloys having Fe concentrations of 20% and 50%, according to a recently proposed approximate theory. In order to have a comparison with experimental data, the XPS valence band shape has been measured for the same concentrations. The experimental widths and shapes of the bands turn out to be well reproduced by the theory. An account of this work has been given at the ?International Conference on Solid Films and Surfaces?, held in Sydney in 1984, and will be published in the Conference Proceedings (1985).     

Hyperfine field distributions in nickel alloys measured by time differential perturbed angular correlations

Hyperfine fields were observed for 1 ppm ¹¹¹Cd in dilute nickel based alloys, showing broad undifferentiated distributions for solutes Si and Cu, but a well defined statellite structure for Fe and Co, as expected for solutes producing large and small host moment disturbances, respectively. Both types of alloys exhibited short range ordering between probe and solute atoms.     

Resistivity- and perturbed angular correlation-study of implanted nickel hydrides

Hyperfine Interactions -     

Study of nanoconfigurations in Zircon-Mullite composites using perturbed angular correlations

It has been already published that, at nanoscopic level, zircon exhibits wide regions of aperiodic material not detected by the ordinary techniques used to analyse the obtained product in the production of ceramic materials. In this paper it is reported how the Perturbed Angular Correlations (PAC) technique has assisted the interpretation of a mismatch between experiment and theoretical estimation of a mechanical property in some zircon-mullite composites. In fact, it has been proved that the difference observed between the calculated and the experimental value of the elastic modulus in composites of the form (1?x) ZrSiO₄ ? x 3Al₂O₃.2SiO₂ (with x = 15, 25, 35 and 45 wt.%) behaves very similarly as the relative amount of aperiodic zircon determined by PAC. This result allows to re-interpret the mullite role during the materials preparation.     

Study of combined magnetic and electric hyperfine interactions for cadmium in Dysprosium by time differential perturbed angular correlations

The combined magnetic and electric hyperfine interaction at the site of a¹¹¹Cd impurity in magnetically ordered Dysprosium has been investigated as a function of temperature by time differential perturbed angular correlation measurements. Three different phases have been found in metallic Dy with transition temperatures of 85 and 179 °K in agreement with the results of bulk material measurements. In the paramagnetic phase above 179 °K a pure electric quadrupole interaction has been observed. The various contributions to the electric fieldgradient are analyzed and it is shown, that the dominant contribution comes from the conduction electrons. In the ferromagnetic phase which extends from 0 to 85 °K the magnetic hyperfine field at the site of¹¹¹Cd has the same temperature dependence as the spontaneous magnetization. The value of the hyperfine field at 4.2 °K is ¦H _eff¦=(221 ± 4) kG. At 85 °K a transition to the antiferromagnetic phase of Dy occurs, which shows a hysteresis of the transition temperature. In the antiferromagnetic phase the temperature dependence of the hyperfine field deviates considerably from the magnetization curve. It is suggested that this deviation might be due to a temperature dependence of thes-f exchange interaction.     

Conversion-electron-gamma and gamma-gamma directional angular correlations in 160Dy

Gamma-gamma and conversion-electron-gamma angular correlations in ¹⁶⁰Dy have been measured for the 298 keV–966 keV and 298 keV–879 keV cascades. Particle parameters of the 966 keV E2 transition were determined to be b₂(E2; e_K) = +1.23±0.08 and b₂(E2; e_{ΣL + ΣM) = +1.27±0.23}. The multipole mixing ratio for the 298 keV radiation was determined to be δ(M2/E1) = +0.04±0.01 and we have confirmed the value δ(E2/M1) = ?13±2 for the 879 keV. The E0–E2 mixture parameter for the 879 keV transition was determined as q_K = ?0.03±0.09 assuming penetration effects to be negligible.     

Investigation of statistically perturbed angular correlations of181Ta at different temperatures

We have time differentially investigated the attenuation of the 133–482 keV cascade of¹⁸¹Ta in hydrofluoric acid at different temperatures. Using a four detector apparatus we were able to measure with eight fold statistics. As a result we found a small attenuation at room temperature which was increased with decreasing temperature of the liquid source. A comparison of ourA ₂(0) andA ₄(0) values with the results of other authors is given.     

Lattice defects in ion-implanted aluminium studied by means of perturbed angular correlations

Migration and clustering of lattice defects after implantation of¹¹¹In in Al and subsequent annealing at temperatures in the range from 80 to 800 K were investigated applying the DPAC technique. The effects of implantation dose, implantation temperature, laser irradiation, and plastic deformation were studied. The measurements on plastically deformed Al were complemented by positron lifetime measurements. We observed four In-defect clusters that can be flagged by well-defined hyperfine interaction parameters, and we determined their symmetry properties by using single-crystal samples. Important conclusions are: (i) monovacancies are not trapped by In-atoms, (ii) small In-defect clusters are formed by direct trapping of divacancies and/or trivacancies, and (iii) extended In-defect clusters are very stable and anneal in the temperature range 600–700 K. Consequences for the interpretation of other measurements on dilute Al(In) alloys are discussed.On leave from Tata Institute of Fundamental Research, Homi Bhabha Road, Bombay 400 005, India.     

Graphite indium chloride studied by time-differential perturbed angular correlations of γ-rays

The technique of time-differential perturbed angular correlations of γ-rays (TDPAC) has been applied to the study of graphite indium chloride using ¹¹¹In as a probe. The results indicate the presence in the intercalated sample of two static quadrupole interactions with frequencies v⁽¹⁾_Q = 55.83±0.04 MHz and v⁽²⁾_Q = 270.44±0.05 MHz, plus a time-dependent interaction with decay constant $\text{1}\text{τ}\text{= (3.288±0.002) × 10}{}^{-2}\text{ns}{}^{-1}$. The electric field gradient components for the static interactions were determined together with corresponding asymmetry and width parameters.     

Determination of nuclear multipole relaxation times by measurements of statistically perturbed angular correlations

It is pointed out that phenomena of nuclear multipole relaxation can also be studied by the observation of perturbed angular correlations. The corresponding formulae are derived and compared with the results of other authors. A compilation of experimental results is presented.     

Oxidation of indium implanted aluminium studied by the Rutherford backscattering and perturbed angular correlation methods

Aluminium foils oversaturated with 5.10¹⁵/cm² implanted¹¹⁵In⁺ ions were oxidized in 200 mbar oxygen or vacuum annealed at 370–870 K. The samples were analyzed by the Rutherford backscattering (RBS) and perturbed angular correlation (PAC) techniques, using some 10¹¹/cm² implanted radioactive¹¹¹In tracers. Furthermore, the oxygen surface profiles were also scanned with high resolution by using the nuclear resonance technique (NRA). The formation of passivating Al₂O₃ surface layers, preventing deeper oxygen diffusion and the indium diffusion into these oxidized surface layers and into the bulk, were studied. Several quadrupole interaction frequencies previously attributed to strained cubic indium precipitates and indium (-vacancy) clusters were observed. When the samples were oxidized above 750 K, the formation of In-O complexes and of substitutional¹¹¹In in Al₂O₃ was observed.     

The hyperfine magnetic field of172Yb in Fe and Ni

Time-differential perturbed angular correlation measurements have been performed on the 91–1095 keV -ray cascade emitted by¹⁷²Yb nuclei in the capture decay of¹⁷²Lu, using implanted sources of¹⁷²Lu in Fe and Ni. From these measurements hyperfine field valuesB(YbFe)=–1253±83 kG andB(YbNi)=–143±12 kG follow at room temperature. From the modulation amplitude of the spectra it follows that only about 20% of the ytterbium nuclei participate in the precession.     

Analytic perturbation functions for static interactions in perturbed angular correlations of ®rays

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.