Magnetic Field Penetration in Superconducting Lead

The magnetic susceptibility of small superconducting lead spheres (radius ∼${10}^{-3\mathrm{}}$ cm) has been determined by a self-inductance method. On the basis of relations derived from the London theory for reducing the data, the penetration depth, $\lambda$, is calculated for three different lead samples at 4.22°K. Results indicate that $\lambda$ is 1.3±0.3×${10}^{-5\mathrm{}}$ cm at this temperature. In addition, it is found that, within experimental error, $\lambda$ is not a function of the size of the sphere. It is noted that there is need for using smaller sized particles and accounting for the interaction effects if future colloid investigations designed to test the London theory are to be successful.