Precise lineshape measurements using an analytic Mossbauer function

Ammar Djedid, Purdue University

Abstract

Using a microfoil conversion electron (MICE) detector capable of operation at low temperature, we have obtained effects of more than 600% for the 46.5 keV line and 17-20% for the 100.1 keV line in $\sp{182}$W, in very good agreement with our theoretical analysis (60). Using 100 Ci $\sp{183}$Ta and 5 Ci $\sp{182}$Ta sources, with LiF and NaCl crystal monochromating filters, we have measured the lineshape parameters for the 46.5 keV and 99.1 keV Mossbauer effect (ME) transitions of $\sp{183}$W and the 100.1 keV transitions of $\sp{182}$W. Using an analytical representation of the convolution integral and utilizing asymptotic analyses of the lineshape, we find, for both transmission and conversion electron (MICE) experiments, accurate values of all ME parameters. The line widths for the 46.5, 99.1, and 100.1 keV transitions are 3.10(4), 0.337(12), and 0.195(3) cm/s, respectively. The interference parameters are $-0.0025(1)$, $-0.0093(12)$, and $-0.0107(12)$ respectively. The agreement between transmission and (MICE) measurements for the above lineshape parameters is within experimental errors. These measurements are the first having sufficient precision to allow a quantitative comparison with dispersion theory (21,24), and they indicate interference parameters 10 to 20% smaller than predicted. Our analysis of the true lineshape and the study of the asymptotics permits a quantitative determination of the isomer lifetimes rather than the usual lower bound found in earlier ME experiments. Using the above analytic function and the ME transitions lines we have measured the recoil free fraction f(T) for metallic tungsten. We have found f(T) to vary from f(298K) = 0.38(2) to f(77K) = 0.74(4). Effective ME characteristics are determined from these recoilless fractions using a Debye model. A double resonance experiment was carried out using the 46.5 keV line. We obtained an improvement in the signal to background four times bigger than with a germanium detector. From the temperature dependence of the area we obtained a ME characteristic which is in agreement with the direct f(T) measurement. Using the exceptionally high signal-to-background ratio for the 46.5 keV line and a MICE detector we have measured the temperature dependence of the ME spectra. The deduced characteristic temperature agrees very well with the two previous measurements. (Abstract shortened with permission of author.)

Degree

Ph.D.

Advisors

Mullen, Purdue University.

Subject Area

Nuclear physics|Condensation

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