Abstract
By taking electron-spin-resonance spectra at 300 Mc/s, rather than at the usual 10 000 Mc/s, the dielectric effect of any water that may be contained in a sample is greatly reduced, and much ‘wetter’ systems can therefore be studied without the necessity of using very small samples. Useful sensitivities are available at this frequency, and the instrument described has a sensitivity of 5 × 1015 spins of crystalline DPPH. The spectrometer can also be used with a suitable x- or gamma-radiation source to enable spectra to be taken during irradiation. Some examples of the growth and decay of free radicals in irradiated wet seeds are given to show the possibilities of the instrument.