STRUCTURE AND ANNEALING OF (N,GAMMA)-INDUCED POINT-DEFECTS IN CAF2

Neutron activated20F nuclei (T1/2=11 s) in CaF2 serve for two purposes: first they produce well defined point defects by their (n, γ)-production mechanism, second, they act as probes to detect the properties of these defects in a β- and γ-ray detected nuclear magnetic resonance experiment. Below about 70 K an interstitial defect is observed due to a quadrupolar splitting of the20F-NMR line. The defect induced electric field gradient is oriented along the 〈111〉-axis of the crystal and causes a quadrupole coupling constant e2qQ/h=-2.0(1) MHz at the20F site. The defect anneals above 70 K with an Arrhenius like temperature dependence corresponding to an activation energy EM=0.17(4) eV. © 1978 Springer-Verlag.