Precise determination of Mössbauer lineshape parameters including interference

Using 100 Ci¹⁸³Ta and 5 Ci¹⁸²Ta 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 of¹⁸³W and the 100.1 keV transition of¹⁸²W. Using an analytic representation of the convolution integral and utilizing asymptotic analyses of the lineshape, we find, for both transmission and microfoil internal conversion (MICE) experiments, accurate values of all ME parameters including width, position, cross section, and interference. This new approach allows deconvolution of source and absorber spectra and gives a simple analytic expression for both as well as their Fourier transforms. The line widths for the 46.5, 99.1, and 100.1 keV transitions are 3.10(10), 0.369(18), and 0.195(12) cm/s, respectively. The interference parameters are -0.00257(9), -0.0093(12), and -0.0107(12) in the same respective order. The agreement between transmission and MICE /1,2/ measurements for the above lineshape parameters is within the experimental errors. We believe these measurements are the first having sufficient precision to allow a quantitative comparison with dispersion theory /3,4/ and they indicate interference parameters 10 to 20% smaller than predicted. Our measured line widths are less than earlier reported values. This is because our analysis of the true lineshape and the study of line asymptotics permits a quantitative determination of the isomer lifetimes rather than the usual lower bound found in earlier ME experiments.