Comments on anomalous muonium in germanium and silicon

Since Graf et al. (ibid., vol.6, p.176, 1979) observed anisotropic muonium in germanium, the dissymmetry between Si and Ge has been partially removed. The main discrepancy with respect to the silicon remains in the low field spectrum, where, while Si frequencies are easily detected down to 20 G, Ge transitions disappear below 2 kG. The authors explore the role of the nuclear superhyperfine interactions with respect to this problem, and see whether the fraction of nuclei having a non-zero spin may be considered responsible for such a behaviour by broadening the linewidths of the mu /sup +/SR signals. In order to calculate the broadening of a MuSR line due to these superhyperfine interactions, the authors have studied a simplified model for the Mu* atom in which only one nuclear spin is introduced, with an average HF energy. This should represent the actual situation with more than one nuclear spin present with different HF constants. (5 refs).