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For example, for the field of 3350 G shown above, spin resonance occurs near 9388.2 MHz for an electron compared to only about 14.3 MHz for .
The larger the difference the larger the intensity detected by the detector tuned to 100 k Hz (note this can be negative or even 0).
When no bones and teeth can be found in prehistoric sites, ESR dating on quartz extracted from sediments has been used to date sites whose ages range over the entire Quaternary period.
The lower spectrum is the first derivative of the absorption spectrum.Combined ESR and U-series dating of fossil herbivore teeth are the only means of dating layers from which such ancient remains have been recovered in western Europe.Good examples are the sites of Atapuerca Gran Dolina, Spain and Visogliano, Italy which have been dated using tooth enamel.By detecting the peak to peak amplitude the first derivative of the absorption is measured.
By using phase sensitive detection only signals with the same modulation (100 k Hz) are detected. Note field modulation is unique to continuous wave EPR measurements and spectra resulting from pulsed experiments are presented as absorption profiles.Furthermore, EPR spectra can be generated by either varying the photon frequency incident on a sample while holding the magnetic field constant or doing the reverse.