Abstract
The electron spin resonance spectra of gamma‐irradiated single crystals of acetyl‐L‐glutamic acid have been measured at 9 and 23.4 kMc/sec for various orientations of the crystal in the external magnetic field. From the analysis of the hyperfine interaction constants, the free radical produced immediately after the irradiation of acetyl‐L‐glutamic acid is thought to be [Complex chemical formula] However, this radical transforms to another more stable one in the half‐life of three days. The structure of the stable free radical is inferred from the hyperfine structure of its electron spin resonance.