ESR Measurement and Irradiation at Variable Temperatures below 77°K

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An apparatus for irradiation and subsequent ESR measurements at variable temperatures below 77°K was constracted by combining an ESR spectrometer, and an X-ray irradiator, and a laboratory scale low temperature refrigerator operating at the temperature region between 77 and 4.2°K. A device for rotating the single crystal specimen was made to measure the angular dependence of the ESR spectra. The lowest specimen temperature achieved was estimated to be 6°K and the precision of the temperature control was less than ±0.5°K for a period of several hours. The apparatus makes it possible to irradiate samples and to measure ESR spectra at any temperature in the range between 77 and 6°K. Some applications for irradiation and ESR measurements at low temperatures are also described. An unstable radical which disappears at about 60°K was found in an irradiated single crystal of L-cystine dihydrochloride. Experimental evidence for the quantum tunnelling of the methyl group in polymethylmethacrylate radical was also found by the temperature dependence of the spectra observed at temperatures lower than 77°K.
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