Correlation between EPR and positron annihilation measurements on γ-irradiated acetyl methionine

The dose dependence of the relative EPR signal intensity and positron lifetime spectrum was measured for γ-irradiated acetyl methionine in the dose range from 0 to 30 Mrad. Angular correlation measurements were performed for the doses 0 and 30 Mrad. The result of the irradiation was the creation of EPR centers and inhibition of positronium formation. For one sample, irradiated with a dose of 30 Mrad, EPR and positron lifetime spectra were followed over a period of 50 days after the irradiation. The inhibiting effect and the EPR signal intensity decreased with time. No simple correlation could be established between the number of EPR centers and the positron annihilation data, but other possible explanations are discussed.