Superconductivity of Tin Isotopes

MEASUREMENTS have been made of the superconducting transition temperatures and critical fields of nearly pure tin isotopes separated by the electromagnetic method; the mean atomic weights provisionally determined by mass spectrograph were 116.2 ± 0.2, 120.0 ± 0.2 and 123.6 ± 0.4. Samples of about 15 mgm. in the form of cylinders 1 cm. long cast in silica tubes were used, and transitions were studied (a) by observing the magnetic moment in a constant small magnetic field (2 gauss) as the temperature was lowered, and (b) by measuring magnetization curves at constant temperatures. The magnetic moments were measured by a ballistic method1, and to improve relative accuracy all three samples were studied together. The transitions were sharp (∼0.01° K. width), and the transition temperatures (Tc), defined as the temperatures (extrapolated to zero field) at which the ratio of magnetic moment to field had half its superconducting value, could be determined with a precision of order 0.001° K. relative to each other. The values of Tc expressed on the 1949 scale2 were: