Superconducting Penetration Depth Measurements in Aluminium at 175 Mc/s

A method is described for finding changes in the penetration depth from changes in the resonant frequency of a helix having a core of the superconductor. Some results have been obtained for pure and impure aluminium samples. At the lowest temperatures that could be reached, there was no significant deviation from a linear variation of the penetration depth λ with z = (1 - t 4 ) -1/2 . The value of d λ/ dz in the range 1.1 ⩽ z ⩽ 1.7 was found to be 5.3 × 10 -6 cm.