Observation of CESR in high‐purity aluminium by a reflection spectrometer

The observation of CESR in a 6N aluminium sample using a reflection spectrometer operating at 21 GHz is reported. The main characteristics of the signal are a g‐factor close to 2 and a linewidth varying from 52 G at liquid He temperature to 190 G at 150 K. A minimum of 38 G is found near 20 K. The results are compared with the many body effect theory of Fredkin and Freedman. Good quantitative agreement is not found with the results of Lubzens et al. The results also indicate a g‐value variation in the phonon dominated regime.