Angular Correlation Studies Research Articles

Photon-photon correlations ine+e−→F*F¯*→Fγ1F¯γ2

The F and F* mesons may be observed in e/sup +/e/sup -/ ..-->.. F*F-bar* ..-->.. F..gamma../sub 1/F-bar..gamma../sub 2/. Kinematic constraints relating the energies and directions of the decay photons can be used to discriminate against backgrounds. This method may also be helpful for the discovery of new baryons and heavier mesons. Detailed studies of the photons' angular correlations can determine the F*F-bar* production amplitudes.

Perturbed angular correlation studies of layered compounds and intercalates

Abstract The recent perturbed angular correlation studies of layered compounds and intercalation compounds performed on 181Ta are reviewed.

A search for inequivalent lattice sites in the charge density wave distorted phases of 1T-TaS2

A perturbed angular correlation study of the nuclear quadrupole interaction at Ta in the commensurate charge density wave (CDW) state of 1T-TaS2 yields two inequivalent lattice sites with a population ratio of 0.86(9):1. The electric-field gradients (EFG's) for the low- and high-frequency site differ by 11.6(7)% and show different asymmetry parameters of eta =0.12(3) and eta =0.19(2), respectively. Both the EFG difference and the asymmetry allow the identification of sites within the star shaped cluster model of Brouwer and Jellinek (1976). In the quasicommensurate CDW state both the asymmetry parameters and the EFG difference remain constant whereas the population ratio and the EFG distribution vary, especially at high temperature. The disintegration of star-shaped clusters could be responsible for these observations. In the incommensurate CDW state a unique site with a 4.8(3)% EFG distribution is observed.

Angular correlation studies of intermediate width structures in 16O + 12C

An angular correlation technique has been utilized to study the spins of several intermediate width resonances in the inelastic scattering of 16O + 12C in the range 19 ⩽ E cm ⩽ 23 MeV. An analysis of the correlations and previously reported angular distributions strongly indicates that interpretations of these structures in terms of a single rotational band are inadequate.

Perturbed angular correlation studies of the relaxation process at 111Cd in the superviscous H 3PO 4 + H 2O system

The time differential gamma—gamma perturbed angular correlation technique has been applied to the system phosphoric acid plus water in its phases of glass, superviscous liquid and normal liquid. For the superviscous case the extension of an existing model for the relaxation process has been used to obtain the temperature dependence of the rotational diffusion coefficient.

Investigation of d-orbital participation in bonding by positron angular correlation

Abstract Whether or not ligand perturbation is necessary for d-orbital contraction and consequent participation in bonding has been controversial till now. A study of angular correlation of positron annihilation radiation on organic sulphides and sulphones gives a direct evidence for the conclusion that ligand perturbation is necessary.

Perturbed angular correlation study of Pd impurity configurations neighbouring the111Cd probe atom in Cu host

The electric field gradients (EFGs) created at the nucleus of 111Cd by Pd impurity atoms in the cubic Cu host are studied by the time differential perturbed angular correlation technique. The observed strong enhancement of near-neighbour (NN) impurity populations to the probe atom permitted the study of the onset of various NN configurations as the impurity concentration was increased from 0.5 to 4.5 at.%. The EFG attributed to one NN Pd impurity agrees very well with NMR data for the same alloy. The temperature dependence of this EFG follows a T3/2 law in the range 80-973K. A measurement at 1173K indicates the presence of dynamical effects on the nuclear quadrupole interaction.

Level Structure of124Te

The level structure of 124 Te has been investigated by studying gamma rays emitted following the beta decay of 124 Sb to the excited states of 124 Te. The intensities of 70 gamma rays observed in this decay have been measured with a better precision than known earlier. The existence of the gamma rays with energies of 1248.62 and 1731.4 keV has been confirmed, whereas the 159.4, 185.4, 385.9, 476.6, 498.4, 553.8, 997.0, 1163.2, 1388.7, 1505.6, 1557, 1950.4, 2151.5 and 2274.0 keV gamma transitions reported earlier have not been observed in the present investigations. The gamma-gamma angular correlation measurements for nine cascades populated in this decay have been done out of which 791-(646)-603 keV cascade has been attempted for the first time. From these measurements, the multipole admixtures in the 714, 723, 791, 968, 1045, 1368, 1691 and 2091 keV transitions have been obtained. These angular correlation studies have enabled us to assign 2 + and 3 - characters to the levels at 2039.5 and 2694.0 keV res...

Stability of lipid vesicles in tissues of the mouse: a gamma-ray perturbed angular correlation study.

The rate of phospholipid vesicle disruption in specific tissues of the mouse was followed by gamma-ray perturbed angular correlation (PAC) spectroscopy. In these studies, high levels of 111In-nitrilotriacetic acid complex are contained in unilamellar vesicles consisting of distearoyl phosphatidylcholine, cholesterol, and small amounts of other lipids which modify the surface properties. The PAC technique monitors the extent of vesicle breakup by measuring a time-integrated perturbation factor, less than G22 (infinity) greater than. As the vesicles are broken open in vivo, the released 111In3+ ions quickly bind to macromolecules and the less than G22 (infinity) greater than value decreases substantially. After administration of vesicles by various routes (intravenous, intraperitoneal, subcutaneous, and oral), the radioactivity and less than G22 (infinity) greater than values were determined for several tissues at intervals up to 24 hr. We conclude from these data that (i) the PAC technique in conjunction with standard gamma counting methods provides unique information on the condition and location of vesicles in specific tissues, (ii) significant differences in vesicle integrity are found in various tissues, and (iii) both the means of administration and the presence of surface charge affect the vesicle stability and distribution. The carbohydrate analogues of cholesterol affect vesicle stability but not distribution.

Time-dependent perturbed angular correlation study of181Ta in Mg

The quadrupole interaction of181Ta in Mg metal has been investigated at room temperature by time differential perturbed angular correlation method yieldingvQ=127±7 MHz. The observed EFG is calculated to be 20.8×1016 V/cm2.

Direct observation of the high-momentum components of the conduction band of copper by two-dimensional angular correlation of annihilation radiation

A high precision study of the two-dimensional angular correlation (2D ACAR) in copper using a multicounter apparatus reveals directly the high-momentum components of the conduction band. The general features of the anisotropy of these “umklapp annihilations” are discussed.

Quadrupole interaction studies of Hg in Sb

Time differential perturbed angular correlation and nuclear orientation studies of the electric quadrupole interaction for Hg in Sb have been performed. The effective field gradients |V zz eff (HgSb)|=1.43(18)×1017V cm−2 at room temperature andV zz eff (HgSb)=+1.8(2) × 1017V cm−2 below 0.05 K have been derived. These two values are no indication for an anomalous temperature dependence of the effective field gradient for Hg in Sb. The value of the electric field gradient fits well into the systematics for Hg in other hosts. It is shown that the electronic enhancements of the field gradients are correlated to the valence of the impurities and are rather insensitive to the host properties.

The high-density proportional chamber and its applications

The recent development of the high-density proportional chamber - a proportional chamber with solid converters - has provided important, new imaging possibilities for low-energy neutral particles. The principal device realized to date is a high spatial resolution (2 mm fwhm) positron camera. This has been used for angular correlation studies of positron annihilation radiation for condensed matter physics research, and for three-dimensional medical imaging of positron radioisotope distributions. For these applications, a new converter, made of bismuth-doped araldite, is described, which combines good detection efficiency (10%) and coincidence time resolution (100 ns) when operated with carbon-dioxide gas. The addition of a gadolinium foil to a high-density proportional chamber affords an efficient detector for thermal neutrons that maintains the good spatial resolution at large angles of neutron incidence. With a hafnium foil, the same proporties are possible for epithermal neutrons. Solar neutrino detection, electrophoresis, and radiochromatography are other fields of possible application.

Perturbed angular correlation studies of chemically generated electric field gradients in Hf compounds

The time-differential-perturbed-angular-correlation (TDPAC) technique has been applied to the study of electric quadrupole interactions in HfO2, HfO(H2PO4) ⋅H2O, and HfP2O7. Strong perturbations were seen in each case, with time evolution characteristic of the static electric field gradients generated by the electron distributions in chemical bonds. Analysis of the experimental data within a theoretical framework has permitted derivation of the electric field gradient parameters associated with the Hf–O bonds in the oxide and the two phosphate compounds. A simple model calculation involving orbital populations appears capable of reproducing the experimental results and provides insight into the bonding features of these relatively complex, but structurally known, systems. The TDPAC signature of each compound appears sufficiently unique so as to offer the possibility of its adaptation as a microscopic probe of more complicated or unknown crystalline and liquid systems.

Anomalously high electric field gradients for Hg in Zn, Cd and Re below 0.05 K

Nuclear orientation and time differential perturbed angular correlation studies of the electric quadrupole interaction of Hg in Zn, Cd and Re have been performed. The interaction frequencies found in the nuclear orientation experiments for 197mHg below 0.05 K, ν Q = +480(20) MHz, ν Q = +430(30) MHz and ν Q = −110(15) MHz in Zn, Cd and Re, respectively, are a factor of about 4 higher than expected from the extrapolation of angular correlation data available down to 105 K.

On the angular correlation of electrons in configuration interaction wavefunctions

In a recent study of angular correlation of electrons in the ground state of the helium atom was examined using both configuration interaction (CI) and Hylleraas wavefunctions. It was concluded that little reliance should be placed on properties involving angular correlation which are derived from CI wavefunctions. In contradiction with this conclusion, we have observed a rapid convergence of the natural orbital CI expansion to the correct angular correlation behavior of the Kinoshita helim atom wavefunction.

A High-Resolution Proportional Chamber Positron Camera and Its Applications

A positron camera consisting of two high density proportional chambers is described. It provides a spatial resolution of 2.4 mm FWHM, a maximum data rate of 3000 c.p.s. and a sensitivity of 25 c.p.s. per μCi. Results of its application to angular correlation studies of condensed matter and to phantom and in vivo medical imaging are presented. A Fourier deconvolution technique is described for obtaining three-dimensional medical images. It uses a generalized matrix inversion by singular value decomposition to modify the low frequency Fourier components.

Angular correlation study of the levels of 97Nb populated in the decay of 97Zr

The level structure of 97Nb has been studied by measuring angular correlations of γ-rays emitted in the decay of 97Zr. The cascades measured were (energies in keV): 355–1750, 355-(602)-1148, 254-(703)-1148, 602–1148 and 703–1148. The deduced correlations permit unique spin-parity assignments to be made for the levels at 1148 ( 7 2 +), 1750 ( 5 2 +) and 1852 ( 5 2 +) keV . Multipole mixing ratios have been deduced for the 254, 355, 602, 703 and 1148 keV transitions.

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

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

Angular correlation study of levels in 16C

Angular correlation measurements using the 14C(t, pγ) 16C reaction result in the following spin assignments to levels in 16C: E x = 1.766 MeV, J = 2; E x = 3.980 MeV, J = 2; E x = 4.083 MeV, J = 3; E x = 4.138 MeV, J = 4.