Spin-spin relaxation times of the E1′ center in quartz with and without irradiation: implications for the formation process of the oxygen vacancies in nature

The pulsed ESR technique was employed in the present study to obtain the spin-spin relaxation times of the E1′ center (an unpaired electron at an oxygen vacancy) in natural quartz with and without irradiation. The relaxation times of the heat treated E1′ center in natural unirradiated quartz of a granite and of uranium ore were 3.5-7.1μs. Electron and gamma ray irradiated quartz showed the relaxation times of 7.1-15.7μs while He ion implanted quartz showed 1.0-2.0μs, much less than the other samples. The intensity of the E1′ center increased in stepwise heating up to 300∘C before decreasing above that temperature except for He implanted sample which showed monotonic decrease on heating. The present experimental results showed that the characteristics of the E1′ center created by high linear energy transfer (LET) radiation is different from that by low LET radiation, suggesting that, in nature, the oxygen vacancies are created by low LET radiation, i.e. external beta and gamma rays, rather than by alpha particles and alpha recoil nuclei.