Some Experimental Improvements in Conversion Electron Moessbauer Spectroscopy

Conversion Electron Mossbauer Spectroscopy (CEMS) is a useful tool for probing the properties of materials. Common tools used include Cylindrical Mirror Analyzer (CMA) electron energy analyzers and Channel Electron Multiplier (CEM) electron detectors. Unfortunately at electron energies like those encountered in CEMS the efficiency of the CEM can be as low as 10%. Since the count rates in CEMS can be very low, this efficiency is intolerable. Also, at present most CMA's for CEMS are large and expensive to construct. In this work a method was developed to improve the efficiency of the detector(CEM). Also a small, easy to construct CMA was built and studied. A third part of this work involved a study of Cosine Broadening, which as a result of geometry broadens the line width in a Mossbauer spectrum. To improve the detector efficiency a material with high secondary electron yield was used to coat the detector cone. To find such a material a method was developed to measure the relative secondary electron yields of materials using a scanning electron microscope. Based on this study a model was developed that predicted an efficiency that was 3.3 times higher when the cone was coated with MgO. Measurements of the efficiency improvements yielded factors of 3.22, 3.46, and 3.35. After the small CMA was constructed a study of line shape as a function of position on the spectrometer's inner cylinder was carried out by both Monte Carlo calculation and experiment. An interesting result is that the resolution of the spectrometer was found to be less than 2% along its entire useful length, not just in the region of focus. This resolution is more than adequate for most Mossbauer work. To study the effects of Cosine Broadening an exact expression for the broadened spectrum was used to computer generate spectra for various geometries. The Lorentzian parameters for these spectra were studied as a function of R/d, where R is the radius of the source and absorber and d is their separation. Also spectra were generated to study the parameter behavior as a function of line position. At three R/d values experimental spectra were obtained and good agreement with the simulated spectra was achieved. Also the effects of these improvements on future experiments and other suggestions for the future are discussed.