Noise Sources in NMR Oscillators and Relaxation Phenomena in Optically Pumped Mercury Isotopes.

摘要

Two investigations are described:the effects of noise in NMR oscillators,and spin relaxation of optically pumped Hg nuclei. A suitable noise model was provided by white-noise forcing of an NMR oscillator based on linearized Bloch equations. Experimental confirmation at the microhertz level was obtained. Measurements of Hg vapor density in one fused silica cell indicated the existence of three Hg-wall binding states. Excited Hg atoms were required to stimulate interstate transitions. Maximum spin-relaxation times for 199Hg measured in glass and fused silica cells were,respectively, 40and 11min for 199Hg and 50and 100sec for 201Hg. In some fused silica cells evidence was found for a magnetic relaxation mechanism whose strength increased rapidly with temperature and may depend on the surface structure of the cell walls. By observing beats in free precession decay of 201Hg electric quadrupole splittings as small as 1mHz were measured. Cell-intrinsic quadrupole splittings as large as 6.5mHz for fused silica and 17mHz for glass were observed. The cell-intrinsic splitting approached zero as the cell-axis-magnetic-field angle approached 55deg. The relaxation rate on fused silica was enhanced after excited Hg atoms had been present in the cell. (Author)