A solid state paramagnetic resonance spectrometer

A spectrometer is described for use in the frequency range 9000 to 10 000 Mc/s and at the fixed temperatures of boiling refrigerants and a small range below obtained by pumping on the liquid. The lowest temperature available is the triple point of hydrogen (14°K). A high sensitivity is achieved by modulating the magnetic field at 115 kc/s. The sensitivity is such that 10 13 atoms of 56 Co have been detected at 20°K with a signal/noise ratio of 3: 1; it is estimated that 2 × 10 -11 moles of the free radical diphenyltrinitro phenyl hydrazyl (DPPH) would be detectable at 290°K.