Date of Award

Spring 1992

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Physics

Program/Concentration

Applied Physics

Committee Director

Gilbert R. Hoy

Committee Member

Desmond Cook

Committee Member

Gary Copeland

Committee Member

Mark Havey

Committee Member

Linda Vahala

Abstract

The 88-keV first-excited nuclear state in 109Ag has a mean lifetime of 57.1 sec and a corresponding natural linewidth of 1.15 x 10-17 eV which is nearly six orders of magnitude narrower than the width for the 93-keV 13.2-μsec state in 67Zn. The 93-keV transition in 67Zn has the narrowest linewidth for which the Mossbauer effect has been observed. The 88-keV transition in 109Ag is obviously a very difficult case for the observation of the Mossbauer effect and provides a stringent test for exploring the practical limits of inhomogeneous line broadening in real single crystals.

In the past, two attempts have produced evidence for the occurrence of the Mossbauer effect in 109Ag. However, more detailed, corroborating results are needed to substantiate such positive results.

This dissertation reports the results of a series of self-absorption experiments using 109Cd-doped single-crystal samples of natural silver to observe the Mossbauer effect in 109Ag. In addition to measuring the temperature dependence of the 88-keV gamma rays emanating from the samples, the changes in the accompanying x rays were also monitored to account for problems associated with the temperature dependence of the solid angle subtended by the detector. The data were analyzed by a parametric model simulating the experiments.

The results of these self-absorption experiments in the vertical geometry indicated a clear, positive Mossbauer effect. The measured effective cross section was only two orders of magnitude smaller than the theoretical value of maximum resonance cross section (4.56x10-20 cm2). Such a large effective cross section implies an effective linewidth (neglecting the effect of the gravitational redshift and the ambient magnetic field) approximately 50 times the natural linewidth. This is a surprisingly small amount of broadening which is currently not understood.

DOI

10.25777/ywz8-8r88

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