Electron Spin Relaxation in Irradiated Solids

摘要

This investigation has four separate sections related to analysis of irradiatedmaterials using pulsed electron paramagnetic resonance (EPR) techniques. The first part documents the design and fabrication of versatile loop-gap resonators (LGR) made of copper-film (CuFlon (superscript R)) for use at various microwave frequencies. The LGRs are almost transparent to 100 KHz magnetic field modulation used in CW-EPR and allow 90% transmission of a 200 ns magnetic field pulse (2.5 mT) used in stepped field electron electron double resonance (STELDOR) experiments. The second part is a multifrequency investigation of the E' center of irradiated vitreous silica. The longitudinal relaxation time, T1, changed little between 1.1 and 9.1 GHz, but was systematically longer at 19.4 GHz. T1 was dependent upon orientation, with T1 values decreasing about 50% between the parallel and perpendicular orientations of the g-tensor with respect to the external magnetic field. The third part is a multifrequency CW and time domain EPR investigation of irradiated L-alanine which is used as a dosimeter for radiation. The time domain EPR analysis shows the presence of spectral diffusion. The fourth part is the development and use of ELDOR techniques to study the spectral diffusion in irradiated L-alanine and other irradiated organic solids. Pulsed STELDOR, and pulsed two-frequency ELDOR methods were developed and the details of the implementation is reported. The assignment of relaxation times that gave the best simulation of the experimental data was an electron relaxation time of 240 microsec, a nuclear relaxation time of 10-12 microsec, and a cross relaxation time of 0.6 microsec. The results showed the power of a multimethod analysis and simulation to assign relaxation times for samples exhibiting spectral diffusion.