A signal-to-noise standard for pulsed EPR

A 2 mm diameter by 10 mm long cylinder of fused SiO2 (quartz) γ-irradiated to 1 kGy with 60Co contains about 2 × 1016 spins/cm3. It is proposed as a standard for monitoring signal-to-noise (S/N) performance of X-band pulsed EPR spectrometers. This sample yields S/N of about 25 on modern spin echo spectrometers, which permits measurement of both signal and noise under the same conditions with an 8-bit digitizer.