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THE QUADRUPOLE INTERATION IN ZINC METAL
W. Potzel, A. Forster, G. Kalvius
To cite this version:
W. Potzel, A. Forster, G. Kalvius. THE QUADRUPOLE INTERATION IN ZINC METAL. Journal
de Physique Colloques, 1979, 40 (C2), pp.C2-29-C2-30. �10.1051/jphyscol:1979208�. �jpa-00218466�
JOURNAL DE PHYSIQUE
Collogue CI, supplement au n° 3, Tome 40, mars 1979, page Cl-l'i
THE QUADRUPOLE INTERACTION IN ZINC METAL*
W. Potzel, A. Forster and G.M. Kalvius
Physik Department, Teehn-tsehe Universitat Uunohen, D-8046 Gavdhing, Germany
Résumé.- Des spectres Mossbauer du zinc métal ont été obtenus avec la transition 1/2-5/2 (93 keV) de
6 7Zn. On trouve que le gradient de champ électrique est de symétrie axiale avec une valeur de eq = +(3,02 + 0,05) 1 01 7 V/cm2.
Abstract.- Mossbauer experiments have been performed with the 93.3 keV 1/2-5/2 transition in 6 7Zn metal. The electric field gradient was found to be axially symmetric with a value of eq =
+(3.02 ± 0.05) 1 0J 7 V/cm2.
The 93.3 keV resonance in G 7Zn possesses an extreme sensivity for the measurement of hyperfine interactions. The nuclear Zeeman splitting can be observed in magnetic fields of -100 Oe /l/. The cen- ter shifts of the resonance patterns of various zinc chalcogenides /2,3/ which all contain the zinc atom in the +2 oxidation state are very large compared to the line width. The quadrupole interaction of the spin _-?. groundstate of 6 7Zn (the excited state has I = -L and thus shows no quadrupole splitting) has been thoroughly studied in ZnO /4/. Only incomplete data were available for zinc metal /5/. In this note we report on measurements to determine the electric
field gradient in zinc metal.
For a source we used 6 7Ga in Cu. The 6 7Ga (T , = 78h.) activity was obtained in situ by irra- diation of a copper foil with 35 MeV a-particles.
The foils were not annealed after irradiation. A single resonance line is emitted.
The absorber consisted of Zn metal powder, en- riched to 89.7% in 6 7Zn, which was annealed at 650 K in argon atmosphere for 12 h. and thereafter slowly (50 K/h.) cooled to room temperature. The absorber thickness was 1.4g67Zn/cm2.
To generate Doppler velocities in the range from ~lum/s to a few lOOum/s a piezoelectric quartz spectrometer /6/ was used, which produced a sinusoi- dal motion with a frequency of ~500 Hz. Data were collected in a modified time mode with a PDP8 compu- ter via a fast interface /7,8/, especially designed for high channel advance rates. The y-rays were de- tected by a Nal-scintillation counter of 2mm thick- ness. The spectrometer was calibrated using the known /4/ quadrupole splitting in ZnO.
This work has been supported by the Bundesministe- rium fur Forschung und Technologie and by the Kernforschungszentrum Karlsruhe.
Figure 1 displays a Mossbauer absorption spec- trum scanned to a maximum velocity of ±65)im/s. The computer fit gives the following results (only the statistical errors are given) :
- center shift S=(15.1 ± 0.2)um/s
- quadrupole interaction e2qQ = + (165 ± 3)ptn/s = (12.4 ± 0.2) MHz.
- average full width at half maximum W =(2.23±0.41) Um/s
- average absorption area A = (7.6 ±0.9) 10-1,'W.
Fig. 1 : Mossbauer spectrum at 4.2 K of a 67GaCu source and a polycrystalline 6 7Zn metal absorber.
Within the accuracy of our experiment the sepa- ration between the three resonance lines is 2:1, in- dicating that the asymmetry parameter ri=0. Using the known /9/ quadrupole moment of Q67(5/2)= 0.17b we find for the electric field gradient in Zn metal, eq = +(3.02 ± 0.05) 1017V/cm2. This value is in fair agreement with a recent theoretical calculation /10/, which gave eq = +(4.05 ± 0.60) 101 7 V/cm2.
Using the results of previous /ll, 12/ measu- rements of quadrupole interactions by perturbed angu- lar correlations and nuclear orientation one may de- rive the following quadrupole moments :
- for the spin-9/2 state in 6 7Zn : Q67(9/2) = +(0.68 ± 0.03)b
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1979208
c2-30 JOURNAL DE PHYSIQUE
-
for the spin-912 state in 6 9 ~ n : ~~'(912) =-(0.38
+
0.05)bThermodynamic and inelastic neutron scattering data 1131 give evidence for a strong anisotropy of the mean square displacement <x2> of the Zn atoms in hexagonal metal. This should lead to differences in the intensities of the hyperfine lines due to the Goldanskii-Karyagin effect /14/. Although the data of figure 1 give some indication of such a behaviour a definite conclusion cannot be drawn within the pre- sent limits of error /15/.
We have performed additional experiments using a 7 ~ a 3 source and an enriched 7 ~ n 0 absorber. The transmission spectrum shows a threeline pattern due to the quadrupole interaction in ZnO. Using the known / 161 Debye-temperature for znO(EIZnO = 309 K)
D
we deduce an effective Debye-temperature for zinc metal of El? 240 K. This value is considerably lower than the results derived from both, calorime- tric (ElZn D = 322 K) and elastic data
(o?
= 328 K)1171. This discrepancy could be due to lattice de- fects in our absorber of Zn metal powder. Zn atoms on (or close to) strongly distorted lattice sites will most likely produce a much larger and smeared out quadrupole pattern, which either escapes detec- tion within the velocity range of the present expe- riment or just contributes to the background inten- sity. For ' ~ n 3 we find an effective recoilfree fraction of -I%, which corresponds to a lower limit for the Debye-temperature of OD
>
260 K. This again is a much lower value than the Debye-temperature of the pure copper matrix (OCU = 343 K) / 181.D
References
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