Mössbauer-Effect Measurements of the Thermal Shift ofSn119inβ−Snbelow 90°K

The shift in the resonant absorption energy of the 23.9-keV transition of ${\mathrm{Sn}}^{119}$ was observed as the temperature of a $\beta$-tin Mössbauer absorber was varied between 90 and 3.6°K. The metallic ${\mathrm{Sn}}^{119m}$ source was kept at constant temperature. A continuously calibrated slope-detection method was employed. The standard deviations of the fractional energy shifts observed were about 0.8 parts in ${10}^{15}$, or 3% of the total thermal shift of approximately 26×${10}^{-15\mathrm{}}$ measured between 77 and 4°K. Earlier measurements of the thermal shift in metallic tin had a statistical accuracy of about 40% over 100°K, and were not extended below 77°K. Such observations were interpreted on the basis of the relativistic time-dilation effect. Because of the improved accuracy of the present measurements, it has been necessary to consider also the temperature variation of the isomer shift and of the quadrupole asymmetry of a preferentially aligned sample in assessing the agreement with theory. The recrystallization texture of the $27-\mu$ absorber foil was analyzed by x-ray methods. A search for a possible small shift in energy at the superconducting transition in tin was also made, using the same apparatus. Measurements were made by alternating the absorber temperature above and below the transition temperature every few minutes. The results indicated no change in the absorption energy within the limits of 0.8 parts in ${10}^{15}$, in accord with previous studies.