Jump Frequencies of Cd Tracer Atoms in L12 Lanthanide Gallides

Jump frequencies of Cd tracer atoms were measured in three lanthanide gallides having the L12 structure: DyGa3, ErGa3 and LuGa3. 111In/Cd impurity probe atoms were observed to occupy the non-cubic Ga-sites through the nuclear quadrupole interaction using the method of perturbed angular correlation of gamma rays (PAC). Measurements at elevated temperatures exhibited nuclear relaxation (damping) of quadrupolar perturbation functions attributed to diffusional jumps of the probes among orientationally inequivalent Ga-sites. Accurate values of jump frequencies were determined from fits of the measured perturbation functions using a model of stochastically fluctuating electric-field gradients, as in previous work [e.g., Matthew O. Zacate, Aurélie Favrot and Gary S. Collins: Physical Review Letters Vol. 92 (2004) p. 225901]. Arrhenius plots of jump frequencies for the three systems exhibited jump-frequency activation enthalpies in the range 0.86-1.05 eV and prefactors of about 2 THz. The activation enthalpy for ErGa3, 0.86(2) eV is compared with those for ErAl3, 1.40(4) eV, and ErIn3, 1.34(5) eV.

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Motion of Cadmium Tracer Atoms in Al11R3 Phases (R=La,Ce,Pr)

Defect and Diffusion Forum ◽

10.4028/www.scientific.net/ddf.289-292.755 ◽

2009 ◽

Vol 289-292 ◽

pp. 755-761 ◽

Cited By ~ 4

Author(s):

Stephanie Lage ◽

Gary S. Collins

Keyword(s):

Gamma Rays ◽

Time Domain ◽

Perturbed Angular Correlation ◽

Nuclear Quadrupole Interaction ◽

Electric Field Gradients ◽

Jump Frequency ◽

Field Gradients ◽

The Mean ◽

Nuclear Quadrupole ◽

Jump Frequencies

Jump frequencies of Cd tracer atoms were measured in three phases having the orthorhombic Al11R3 structure, with R= La, Ce, or Pr. The structure has four inequivalent Al-sites and two inequivalent R-sites. 111In/Cd tracer atoms were observed to occupy several sites via the nuclear quadrupole interaction using perturbed angular correlation of gamma rays (PAC). Time-domain PAC spectra became damped as the temperature increased, which is attributed to nuclear relaxation caused by diffusional jumps of Cd tracer atoms leading to changes in orientations and/or magnitudes of electric field gradients (EFG’s). Maximum relaxations were observed near 770 K. A method is proposed for estimating the mean jump frequency at that temperature, giving a mean jump frequency w averaged over all sites of about 100 MHz. At still higher temperatures, damping decreased due to motional averaging, and the quadrupole perturbations evolved into unique signals having lower frequencies and corresponding in each phase to the averages of EFG tensors of all sites visited by the Cd tracer atoms. For Al11La3, the jump frequency at 1073 K was estimated to be 1.9 GHz. Such jump frequencies imply unusually high diffusivities in these phases.

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Diffusion in LanCoIn3n+2 Phases Studied by Perturbed Angular Correlation

Defect and Diffusion Forum ◽

10.4028/www.scientific.net/ddf.323-325.453 ◽

2012 ◽

Vol 323-325 ◽

pp. 453-458 ◽

Cited By ~ 2

Author(s):

Randal Newhouse ◽

Gary S. Collins

Keyword(s):

Angular Correlation ◽

Perturbed Angular Correlation ◽

Diffusion Mechanism ◽

The Other ◽

Electric Field Gradients ◽

Jump Frequency ◽

Quadrupole Relaxation ◽

Field Gradients ◽

Jump Frequencies ◽

Nuclear Quadrupole Relaxation

Jump frequencies of 111In/Cd tracer atoms were measured for a series of layered phases LanCoIn3n+2 using the technique of perturbed angular correlation of gamma rays (PAC). The frequencies were determined by analysis of nuclear quadrupole relaxation produced by fluctuating electric field gradients. Samples were synthesized having nominal values n= 1, 2, 3, 5 and , with n= corresponding to the L12 phase LaIn3. The phases form heuristically from LaIn3 by replacing every (n+1)th (100) mixed plane of La and In atoms with a plane of Co-atoms. For the n=1 phase, LaCoIn5, jump frequencies were too small to detect. Two signals were observed, one for indium atoms next to the Co-planes and the other for more distant indium atoms. No relaxation was observed for atoms next to the Co-planes, indicating that there is no diffusion across the Co-planes. With increasing n, jump rates for the other In-atoms increased toward values observed for LaIn3. Jump frequency activation enthalpies for n= 3 and 5 were observed to be the same as for n=, suggesting the same diffusion mechanism. However, the jump-frequency prefactors were found to be smaller for small n, which is attributed to reductions in the connectivity of the diffusion sublattice. We conclude that diffusion in the layered phases is remarkably similar to diffusion in LaIn3 once the reduced connectivity is taken into account.

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Diffusion in Intermetallic Compounds Studied Using Nuclear Quadrupole Relaxation

Defect and Diffusion Forum ◽

10.4028/www.scientific.net/ddf.237-240.195 ◽

2005 ◽

Vol 237-240 ◽

pp. 195-200 ◽

Cited By ~ 14

Author(s):

Gary S. Collins ◽

A. Favrot ◽

L. Kang ◽

D. Solodovnikov ◽

Matthew O. Zacate

Keyword(s):

Intermetallic Compounds ◽

Gamma Rays ◽

Perturbed Angular Correlation ◽

Nuclear Quadrupole Interaction ◽

Jump Frequency ◽

Quadrupole Relaxation ◽

Boundary Composition ◽

Nuclear Quadrupole ◽

Jump Frequencies ◽

Nuclear Quadrupole Relaxation

The jump frequency of Cd tracer atoms was measured as a function of temperature in seven rare-earth tri-indide intermetallic compounds having the L12, or Cu3Au, structure. The frequency, proportional to the diffusivity, was detected by relaxation of nuclear quadrupole interaction at Cd nuclei caused by reorientation of the electric field gradient in each diffusive jump. Measurements were made using perturbed angular correlation of gamma rays, sensitive to jump frequencies in the range 1-1000 MHz. Results are as follows. (1) Jump frequencies measured in LaIn3 and CeIn3 were observed to be 10-100 times greater at the more In-rich boundary composition than the less In-rich boundary composition, even though the phases appear as line compounds in phase diagrams. (2) Arrhenius plots of the jump frequency were fitted to activation enthalpies that increase from 0.535 to 1.80 eV across the series of phases LaIn3, CeIn3, PrIn3, and NdIn3.

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Nuclear Quadrupole Interaction at 187W(β-)187Re in Tungsten Compounds

Zeitschrift für Naturforschung A ◽

10.1515/zna-1998-6-712 ◽

1998 ◽

Vol 53 (6-7) ◽

pp. 323-339

Author(s):

Pit Schmidt ◽

Torsten Soldner ◽

Wolfgang Tröger ◽

Xinbo Ni ◽

Tilman Butz ◽

...

Keyword(s):

Experimental Data ◽

Quadrupole Interaction ◽

Asymmetry Parameter ◽

Perturbed Angular Correlation ◽

Nuclear Quadrupole Interaction ◽

Electric Field Gradients ◽

Field Gradients ◽

Time Differential ◽

Nuclear Quadrupole ◽

Good Agreement

.6(The nuclear quadrupole interaction at 187W(β-)187 Re was determined by time differential perturbed angular correlation in WC, WS2, WSe2, WSi2, and CaWO4 to be (at 300 K): vQ = 335.9(2), 1094.9(1), 10311), 1131,5( 1), and 1085.9( 1) MHz, respectively. The asymmetry parameter ƞwas zero in all cases. For WSe2 and CaWO4 the temperature dependence of the nculear quadrupole interaction was determined between 300 K and about 900 K. Ab initio calculations of electric field gradients, using the WIEN95-code, were carried out for WC, WS2, WSe2, and WSi2 at W-sites and Re-impurities, and for CaWO4 at W-sites. Good agreement with experimental data was found.

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Diffusion in Binary and Pseudo-Binary L12 Indides, Stannides, Gallides and Aluminides of Rare-Earth Elements as Studied Using Perturbed Angular Correlation of 111In/Cd

Defect and Diffusion Forum ◽

10.4028/www.scientific.net/ddf.323-325.447 ◽

2012 ◽

Vol 323-325 ◽

pp. 447-452

Author(s):

Randal Newhouse ◽

Justine Minish ◽

Gary S. Collins

Keyword(s):

Rare Earth ◽

Angular Correlation ◽

Perturbed Angular Correlation ◽

Diffusion Mechanism ◽

Jump Frequency ◽

Quadrupole Relaxation ◽

System A ◽

Field Gradients ◽

Ordered Intermetallic ◽

Jump Frequencies

Diffusional jumps can produce fluctuating electric field gradients at nuclei of jumping atoms. Using perturbed angular correlation of gamma rays (PAC), jumps of probe atoms cause nuclear quadrupole relaxation that can be fitted to obtain the mean jump frequency. An overview is given of the application of this approach to highly ordered intermetallic compounds having the L12(Cu3Au) crystal structure. New results are then presented for jump frequencies of111In/Cd probe atoms in pseudo-binary L12compounds of the forms In3(La1-xPrx) and (In1-xSnx)3La. For the mixed rare-earth system, jump frequencies are found to scale with composition between jump frequencies of the end-member phases In3La and In3Pr. However, for the mixed sp-element system, a large decrease in jump frequency is observed as Sn atoms substitute for In-atoms. This difference in behavior appears to depend on whether atomic disorder is on the diffusion sublattice (In-Sn substitution), as opposed to a neighboring sublattice (La-Pr substitution), whether or not there is a difference in diffusion mechanism between end-member phases, and/or whether or not there is a valence difference between the mixing atoms. All three conditions apply for only (In1-xSnx)3La.

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A Comparative Time Differential Perturbed Angular Correlation Study of the Nuclear Quadrupole Interaction in HfF4·HF·2H2O Using 180mHf and 181Hf(β–)181Ta as Nuclear Probes: Is Ta an Innocent Spy?

Zeitschrift für Naturforschung A ◽

10.1515/zna-2009-1-215 ◽

2009 ◽

Vol 64 (1-2) ◽

pp. 103-111 ◽

Cited By ~ 3

Author(s):

Tilman Butz ◽

Satyendra K. Das ◽

Yurij Manzhur

Keyword(s):

Electric Field ◽

Frequency Distribution ◽

Quadrupole Interaction ◽

Nuclear Quadrupole Interaction ◽

Electric Field Gradients ◽

Rapid Loss ◽

Field Gradients ◽

Small Admixture ◽

Time Differential ◽

Nuclear Quadrupole

We report on a comparative study of the nuclear quadrupole interaction of the nuclear probes 180mHf and 181Hf(β −)181Ta in HfF4・HF・2H2O using time differential perturbed angular correlations (TDPAC) at 300 K. For the first probe, assuming a Lorentzian frequency distribution, we obtained ωQ= 103(4) Mrad/s, an asymmetry parameter η = 0.68(3), a linewidth δ = 7.3(3.9)%, and full anisotropy within experimental accuracy. For the second probe, assuming a Lorentzian frequency distribution, we obtained three fractions: (1) with 56.5(7)%, ωQ= 126.64(4) Mrad/s and η = 0.9241(4) with a rather small distribution δ = 0.40(8)% which is attributed to HfF4・HF・2H2O; (2) with 4.6(4)%, ωQ = 161.7(3) Mrad/s and η = 0.761(4) assuming no line broadening which is tentatively attributed to a small admixture of Hf2OF6・H2O; (3) the remainder of 39.0(7)% accounts for a rapid loss of anisotropy and is modelled by a perturbation function with a sharp frequency multiplied by an exponential factor exp(−λ t) with λ = 0.55(2) ns−1. Whereas the small admixture of Hf2OF6・H2O escapes detection by the 180mHf probe, there is no rapid loss of roughly half the anisotropy as is the case with 181Hf(β −)181Ta. This loss could in principle be due to fluctuating electric field gradients originating from movements of nearest neighbour HF adducts and/or H2O molecules after nuclear transmutation to the foreign atom Ta which are absent for the isomeric probe. Alternatively, paramagnetic Ta ions could lead to fluctuating magnetic dipole fields which, when combined with fluctuating electric field gradients, could also lead to a rapid loss of anisotropy. In any case, Ta is not an “innocent spy” in this compound. Although 180mHf is not a convenient probe for conventional spectrometers, the use of fast digitizers and software coincidences would allow to use all γ -quanta in the stretched cascade which would greatly improve the efficiency of the spectrometer. 180mHf could also serve as a Pu analogue in toxicity studies.

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Diffusion and Equilibration of Site-Preferences Following Transmutation of Tracer Atoms

Diffusion Foundations ◽

10.4028/www.scientific.net/df.19.61 ◽

2018 ◽

Vol 19 ◽

pp. 61-79 ◽

Cited By ~ 1

Author(s):

Gary S. Collins

Keyword(s):

Diffusion Mechanism ◽

Nuclear Quadrupole Interaction ◽

Site Preference ◽

Jump Frequency ◽

Heavy Lanthanide ◽

Site Preferences ◽

Lanthanide Elements ◽

Light Lanthanides ◽

Diffusion Mechanisms ◽

Jump Frequencies

Using the method of perturbed angular correlation of gamma rays, diffusional jump-frequencies of probe atoms can be measured through relaxation of the nuclear quadrupole interaction. This was first shown in 2004 for jumps of tracer atoms that lead to reorientation of the local electric field-gradient, such as jumps on the connected a-sublattice in the L12 crystal structure. Studies on many such phases using the 111In/Cd PAC probe are reviewed in this paper. A major finding from a 2009 study of indides of rare-earth elements, In3R, was the apparent observation of two diffusional regimes: one dominant for heavy-lanthanide phases, R= Lu, Tm, Er, Dy, Tb, Gd, that was consistent with a simple model of vacancy diffusion on the In a-sublattice, and another for light-lanthanides, R= La, Ce, Pr, Nd, that had no obvious explanation but for which several alternative diffusion mechanisms were suggested. It is herein proposed that the latter regime arises not from a diffusion mechanism but from transfer of Cd-probes from In-sites where they originate to R-sites as a consequence of a change in site-preference of 111Cd-daughter atoms from In-sites to R-sites following transmutation of 111In. Support for this transfer mechanism comes from a study of site-preferences and jump-frequencies of 111In/Cd probes in Pd3R phases. Possible mechanisms for transfer are described, with the most likely mechanism identified as one in which Cd-probes on a-sites transfer to interstitial sites, diffuse interstitially, and then react with vacancies on b-sites. Implications of this proposal are discussed. For indides of heavy-lanthanide elements, the Cd-tracer remains on the In-sublattice and relaxation gives the diffusional jump-frequency.

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Thermal Defects in B2 Iron Aluminide

MRS Proceedings ◽

10.1557/proc-552-kk4.2.1 ◽

1998 ◽

Vol 552 ◽

Cited By ~ 5

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.

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Environmental considerations

10.1093/oso/9780199565092.003.0012 ◽

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.

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