The measurement of the apparent nuclear spin-spin relaxation times of N.Q.R. signals in the ultra-high-frequency region

1981 ◽  
Vol 34 (3) ◽  
pp. 641 ◽  
Author(s):  
PJ Bryant ◽  
S Hacobian
Keyword(s):  
Spin Relaxation ◽  
High Frequency ◽  
Relaxation Times ◽  
Principal Component ◽  
Coaxial Line ◽  
Crystal Defects ◽  
Electric Field Gradients ◽  
High Frequency Region ◽  
Pulse Detection ◽  
Field Gradients

Apparent spin-spin relaxation times, T2*, for the 127I nuclear quadrupole resonances of a series of substituted iodobenzenes were measured by the Doolan-Hacobian double-pulse detection technique. A coaxial line oscillator capable of operation to 800 MHz was used to obtain the signals of the higher frequency transitions. It is shown that the ratio of the T2* measurements of the lower to the upper transition in spin 5/2 systems is of the order of two. This is in accordance with the assumption that the broadening is mainly electrical in nature and arises from the spread in the principal component of the electric field gradients produced by crystal defects.

The Measurement of the Apparent Nuclear Spin-Spin Relaxation Times of N.Q.R. Signals in the Very-High-Frequency Region

1979 ◽  
Vol 32 (2) ◽  
pp. 243 ◽  
Author(s):  
PJ Bryant ◽  
S Hacobian
Keyword(s):  
Crystal Field ◽  
Spin Relaxation ◽  
Nuclear Spin ◽  
High Frequency ◽  
Relaxation Times ◽  
Frequency Region ◽  
Very High Frequency ◽  
High Frequency Region ◽  
Pulse Detection ◽  
Very High

The Doolan-Hacobian n.q.r. double pulse detection technique is described for the measurement of n.q.r, apparent spin-spin relaxation times as applied to a v.h.f. lecher line super-regenerative spectrometer. Results are presented for the linewidths of the 79Br and 81Br resonances in p-dibromobenzene. It was found that crystal-field inhomogeneities produce significant broadening of the n.q.r. signal.

NMR Imaging and the Electric Quadrupole Interaction in Solid Materials

1990 ◽  
Vol 217 ◽  
Author(s):  
B. H. Suits
Keyword(s):  
Quadrupole Interaction ◽  
Relaxation Times ◽  
Electric Quadrupole ◽  
Nmr Imaging ◽  
Electric Quadrupole Interaction ◽  
Electric Field Gradients ◽  
Frequency Shifts ◽  
Field Gradients ◽  
Nuclear Quadrupole Moment ◽  
The Magnetic Field

ABSTRACTNuclei with a spin, 1 > 1/2, possess a nuclear quadrupole moment which can couple to the electric field gradients in a material. They can be static, leading to NMR frequency shifts, or dynamic, which can influence relaxation times. In either case, an NMR image can be made which is sensitized to changes in the electric quadrupole interaction to provide a sensitive measure of the macroscopic spatial dependence of the microscopic changes in the material. Several examples are presented. Special considerations need to be given in the case when the strength of the Zeeman interaction between the nucleus and the magnetic field and/or the rf field is small compared to the electric quadrupole interaction.

Cu NQR Studies of the Superconductors YBa2Cu3Ox and YBa2Cu4O8

1990 ◽  
Vol 45 (3-4) ◽  
pp. 393-400 ◽  
Author(s):  
D. Brinkmann
Keyword(s):  
Pressure Dependence ◽  
Oxygen Deficiency ◽  
Relaxation Times ◽  
Electric Field Gradients ◽  
Field Gradients ◽  
Temperature And Pressure ◽  
University Of Zurich ◽  
The University ◽  
Knight Shifts

Abstract The paper reviews some copper NQR studies in the superconductors YBa2Cu3Ox and YBa2Cu4O8 performed at the University of Zürich. The following topics are discussed: the temperature and pressure dependence of the NQR frequencies; relation between linewidths and oxygen deficiency; the determination of the electric field gradients (EFG) and Knight shifts at the copper sites; discussion of some calculations of the EFG tensors; measurements of the various relaxation times in all phases. The results obtained in both structures are compared; possible interpretations are discussed.

Thermal Defects in B2 Iron Aluminide

1998 ◽  
Vol 552 ◽  
Author(s):  
Gary S. Collins ◽  
Luke S.-J Peng ◽  
Mingzhong Wei
Keyword(s):  
Quadrupole Interaction ◽  
Gamma Rays ◽  
High Frequency ◽  
Perturbed Angular Correlation ◽  
Formation Enthalpy ◽  
Electric Field Gradients ◽  
Quadrupole Interactions ◽  
Field Gradients ◽  
Fractional Concentration ◽  
Charge Calculations

ABSTRACTThermal defects in B2 FeAl samples with compositions between 49.5 and 54.7 at.% Fe were investigated using perturbed angular correlation of gamma rays (PAC). Vacancies on the Fe-sublattice were detected through quadrupole interactions induced at adjacent 111In/Cd probe atoms on the Al-sublattice. Five high-frequency quadrupole-interaction signals were detected (greater than 50 Mrad/s) that are attributed to complexes involving 1, 2, 3, 4 and (with less certainty) 5 Fe-vacancies in the first neighbor shells of the probes. These attributions are based on (1) a comparison between measured quadrupole interaction parameters and point-charge calculations of electric-field gradients for possible vacancy-probe complexes; and (2) numerical simulation of the evolution of site fractions of probes in the complexes at lower temperatures. Measurements were made at temperatures up to 950 C. Assuming that the equilibrium high-temperature is the triple defect (2 Fe-vacancies and one Fe-antisite atom), measurements over the range 600–900 °C yield a formation enthalpy of 1.1(1) eV for the triple defect. Below about 600 °C, Fe-vacancies are quenched-in with a fractional concentration of the order of 1 at.% close to stoichiometry. However, quenched-in vacancies continue to jump over short distances and trap next to the impurity probes atoms in day-long measurements down to 200 °C. Simulations of site fractions below 700 °C were used to determine binding enthalpies of vacancies with probe complexes. Binding enthalpies obtained for the first four vacancies were 0.23, 0.23, 0.15 and 0.18 eV. Simulations in the range 200–700 °C suggest a negative value for the formation entropy. The negative value indicates either that triple defects stiffen the B2 lattice or that repulsive defectdefect interactions become important at the high defect concentrations in FeAl.

Environmental considerations

2017 ◽  
Author(s):  
A. G. Wright
Keyword(s):  
Magnetic Fields ◽  
Collection Efficiency ◽  
Liquid Argon ◽  
Harsh Environments ◽  
Oil Well ◽  
High Permeability ◽  
Electric Field Gradients ◽  
Field Gradients ◽  
High Shock ◽  
Power Spectral

Magnetic fields, with a magnitude comparable with that of the earth (10−4 tesla), affect trajectories of electrons and hence gain and collection efficiency. The inclusion of a high-permeability shield usually offers sufficient protection. Photomultiplier (PMT) performance is affected by electric field gradients generated by the proximity of a metal housing. The design criteria of such housings are discussed. Strong magnetic fields of the order of a tesla require special devices. Operation in harsh environments such as those encountered in oil well logging requires performance at high temperature (200 °C) and in situations of high shock and vibration expressed in terms of power spectral density. Rugged PMTs can meet all these requirements. Applications at cryogenic temperatures, such as liquid argon, can also be met with special PMTs.

Effects of non-axial electric field gradients on the ferromagnetic state of amorphous rare-earth alloys

1980 ◽  
Vol 58 (5) ◽  
pp. 629-632 ◽  
Author(s):  
H. Hernandez ◽  
R. Ferrer ◽  
M. J. Zuckermann
Keyword(s):  
Rare Earth ◽  
Electric Field ◽  
Ferromagnetic State ◽  
Rare Earth Alloys ◽  
Electric Field Gradients ◽  
Axial Electric Field ◽  
Ferromagnetic Alloys ◽  
Field Gradients ◽  
Ordered State

We discuss the influence of non-axial electric field gradients on the ordered state of amorphous ferromagnetic alloys containing rare-earth atoms.

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