Comparison of continuous wave, spin echo, and rapid scan EPR of irradiated fused quartz

Abstract

The E′ defect in irradiated fused quartz has spin lattice relaxation times (T1) about 100 to 300 μs and spin-spin relaxation times (T2) up to about 200 μs, depending on the concentration of defects and other species in the sample. These long relaxation times make it difficult to record an unsaturated continuous wave (CW) electron paramagnetic resonance (EPR) signal that is free of passage effects. Signals measured at X-band (~9.5 GHz) by three EPR methods: conventional slow-scan field modulated EPR, rapid scan EPR, and pulsed EPR, were compared. To acquire spectra with comparable signal-to-noise, both pulsed and rapid scan EPR require less time than conventional CW EPR. Rapid scan spectroscopy does not require the high power amplifiers that are needed for pulsed EPR. The pulsed spectra, and rapid scan spectra obtained by deconvolution of the experimental data, are free of passage effects.

Rapid-scan EPR of immobilized nitroxides

“…The region in which signal amplitude increases linearly with B 1 extends to higher B 1 for the rapid-scan experiments than for CW, which permits use of higher microwave power without saturating the signal. This phenomenon has been observed previously in rapid scans of the E' center in irradiated fused quartz [4], nitroxides in fluid solution [2], amorphous hydrogenated silicon [5], N@C 60 diluted in C 60 [5], and the neutral single substitutional nitrogen centers (N S 0 ) in diamond [5]. In a rapid scan experiment the spin system is on resonance for a time that is shorter than in conventional CW, so higher B 1 can be used without saturation.…”

“…Deconvolution of the rapid-scan signal gives the absorption spectrum. Rapid-scan EPR has been shown to yield improved signal-to-noise ( S/N ) per unit time relative to continuous wave (CW) EPR for rapidly-tumbling nitroxides in fluid solution [2], spin-trapped superoxide [3], the E' center in irradiated fused quartz [4], amorphous hydrogenated silicon [5], N@C 60 diluted in C 60 [5], and the neutral single substitutional nitrogen centers (N S 0 ) in diamond [5]. With the exception of the piece-wise acquisition of the Hyde lab [6], the widest rapid-scan spectra reported so far were the 55 G scans of spin-trapped superoxide at X-band [3].…”

Rapid scan electron paramagnetic resonance at 1.0 GHz of defect centers in γ-irradiated organic solids

“…Sensitivity and signal-to-noise ( S/N ) are major challenges in low frequency EPR experiments (Rinard et al, 2011). Rapid-scan EPR at X-band (~ 9.5 GHz) has been shown to yield improved S/N per unit time relative to CW EPR by a factor of 2 for rapidly-tumbling nitroxides in fluid solution (Mitchell et al, 2012), by factors of 6 to 30 for immobilized nitroxides (Yu et al, 2014), by factors of 10 to 40 for spin-trapped superoxide (Mitchell et al, 2013a), by a factor of 8 for the E′ center in irradiated fused quartz (Mitchell et al, 2011), by more than a factor of 250 for amorphous hydrogenated silicon (Mitchell et al, 2013b), by a factor of 25 for N@C 60 diluted in C 60 (Mitchell et al, 2013b), and by more than a factor of 140 for the neutral single substitutional nitrogen centers (N S 0 ) in diamond (Mitchell et al, 2013b). At 250 MHz rapid scan improves S/N relative to CW by about a factor of 10 for EPR imaging (Biller et al, 2015; Biller et al, 2014).…”

X-Band Rapid-Scan Electron Paramagnetic Resonance of Radiation-Induced Defects in Tooth Enamel

“…Deconvolution of the rapid-scan signal gives the absorption spectrum. Rapid-scan EPR has been shown to yield improved S/N per unit time relative to CW EPR for rapidly tumbling nitroxides in fluid solution (6), immobilized nitroxides (7), spin-trapped superoxide (8), the E′ center in irradiated fused quartz (9), amorphous hydrogenated silicon (10), N@C 60 diluted in C 60 (10) and the neutral single substitutional nitrogen centers (N S 0 ) in diamond (10). The improved S/N for rapid-scan relative to CW spectra comes from three factors: 1.…”