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NATURAL LINEWIDTH OF THE 93.3 keV
γ-TRANSITION IN 67Zn+
W. Potzel, A. Forster, G. Kalvius
To cite this version:
JOURNAL DE PHYSIQUE Colloque C6, supplement au no 12, Tome 37, Decembre 1976, page C6-691
NATURAL LINEWIDTH
OF
THE
93.3
keV
y-TRANSITION
IN
67Zn
+W. POTZEL, A. FORSTER and G. M. KALVIUS Physik Department, Technische Universitat Munchen, Munich Germany
R6sumB. - En utilisant un monocristal de (Ga)ZnO comme source et un monocristal de ZnO nature1 comme absorbant, on a observe pour la transition de 93,3 keV de 67Zn une largeur de raie de (0.36 f 0.04) pmls. AprBs correction de l'effet d'epaisseur des absorbants et dans la limite des erreurs, cette largeur est Bgale a la largeur de raie minimale deduite d'une duree de vie de 13,4 ps pour le niveau de 93,3 keV.
Abstract. - Using a (Ga)ZnO single crystal source in combination with a single crystal absorber of natural ZnO a resonance linewidth of (0.36 f 0.04) pm/s was observed for the 93.3 keV tran- sition in 67Zn. After correction for finite absorber thickness this width equals within the limit of error the minimum observable linewidth as deduced from a lifetime of 13.4 ps for the 93.3 keV state.
The 93 keV resonance in 67Zn has the highest relative energy resolution of the established Mossbauer isotopes. Spectra published thus far, however, show a resonant linewidth of more than 2.5 times the minimum value, derived from lifetime measurements of the 93.3 keV states. In this communication we report on experiments where the natural linewidth has been observed. The measurements were performed with (Ga)ZnO sources against ZnO absorbers.. The 67Ga (T,,, = 78 h) activity was obtained in situ by 11 MeV deuteron bombardment [1] of ZnO single crystals, containing the zinc isotopes in their natural abundances. The single crystals consisted of discs of 4 mm diameter and 0.35 mm thickness. The c-axis was oriented perpendicular to the faces. The direction of observation of the y-rays was parallel to the c-axis. After irradiation the sources were annealed in oxygen atmosphere at 1 000 K for about 12 hours and there- after slowly (50 K/h) cooled t o room temperature.
The ZnO absorbers were of two types :
a) ZnO powder enriched to 85.2
%
in 67Zn with a thickness of 963 mg 67Zn/cm2. The ZnO powder was sintered in oxygen atmosphere a t 1000 K for 24 hours and thereafter slowly cooled to room tem- perature.b) A stack of 9 single crystal discs of natural ZnO, each identical in physical size and orientation to the ones wed for the sources described above. Absorber thickness is 58 mg 67Zn/cm2.
The Doppler velocities were generated by a piezo- (*) Supported by the Bundesministerium fiir Forschung und
Technologie.
electric quartz drive, based on the spectrometer described by G. J. Perlow [2], but with some modifi- cations in design [3]. The y-rays were detected by a NaI-scintillation counter of 2 mm thickness. The data pulses were collected with the help of a compute- rized system [4]. Our spectrometer was calibrated using absorber a) and the known [5] quadrupole splitting in ZnO. Figure l a displays a typical spectrum for a velocity range of
+
12 pm/s. The intensity- 4 - 2 -2 - 1 0 1 2 3 4
VELOCITY [ ~ n ~ l s l
FIG. 1. - 67Zn Mossbauer spectra obtained with a single crystal source and (a) an enriched polycrystalline ZnO absorber, (b) a single crystal absorber of natural ZnO. Both source and
absorber were at 4.2 K.
C6-692 W. POTZEL, A. FORSTER AND G. M. KALVIUS
ratios of the four lines are in good agreement with theory [6]. Figure l b shows the spectrum of absorber b) for a velocity range of
+
4 pm/s. The width of the line is (0.36+
0.04) pm/s.After correction for absorber thickness [7] a linewidth of (0.33
+
0.04) p / s was deduced. This number should be compared with the minimal obser- vable width of 0.31 pmls as calculated using a value of 13.4 ps for the life time of the 93.3 keV state [8]. The absorption dip is (1.70+
0.04) x leading to a Debye-temperature of 8,, = (309 f 10) K forZnO. This value is in good agreement with those determined by other methods [6].
Our results indicate that the radiation damage produced in ZnO by the deuteron bombardment can be annealed completely by the procedure described above. No appreciable after effects exhibiting different charge states of the Zn ion due to the electron capture decay and Auger processes seem to be present at the time of the y-transition. All emitting Zn ions appear to be in the normal charge state and on undisturbed lattice sites.
References
[I] We wish to thank Dr. HUENGES, E., WARMT, R. and the cyclotron group in Munich for performing the irradia- tions.
[2] PERLOW, G. J., in Perspectives in Mossbauer Spectroscopy
S. G . Cohen and M. Pasternak, eds. (Plenum Press, New York) 1972, pp. 221-237.
[3] Details will be published elsewhere.
[4] FORSTER, A., HALDER, N., KALVIUS, G. M., POTZEL, W. and ASCH, L., J. Physique Colloq. 37 (1 976) C 6.
[5] PERLOW, G. J., POTZEL, W., XIASH, R. M. and DE WAARD, H.,
J. Physique CoNoq. C 6 (1974) C6-197.
[6] PERLOW, G. J., CAMPBELL, L. E., CONROY, L. E. and POT-
ZEL, W., Phys. Rev. B 7 (1973) 4044.
[7] HEBERLE, J. and FRANCO, S., Z. Naturforsch. 23a (1968) 1439 and 25a (1970) 134.
