ELECTRON-SPIN RELAXATION-TIMES OF IRRADIATED ALANINE

Crystalline alanine samples were irradiated with Co-60 gamma-rays with doses of 2.7, 11, 60, or 100 kGy. The radicals produced per 100 eV of radiation (G) was dose dependent and systematically higher for L-alanine than for DL-alanine. The value of the electron spin-lattice relaxation time (T(l)) for the room temperature persistent radical is ca. 20 to 50 mus. at X-band (ca. 9.1 GHz) - the longer values were observed near the center of the spectrum. At X-band the electron spin phase memory time T(m) is 100 to 200 ns, depending on radiation dose. For a given dose, T(l) and T(m) are longer for DL-alanine than for L-alanine. The CW EPR linewidth is not relaxation determined and the CW EPR signal is easily saturated. Hence, caution must be exercised when EPR is used for quantitative radiation dosimetry. Relaxation times are shorter at S-band than at X-band.