Critical currents due to flux pinning in cylinders of type I superconductor (Pb-Ag)

Some preliminary studies of flux pinning in cylinders of type I superconductors are reported (12 μ silver powder in lead). These show that when a magnetic field appreciably greater than $\text{1}\text{2}\text{H}{}_{\mathrm{c}}$ is applied perpendicular to the sample axis, the critical current densities are fairly small (e.g. 5.5 × 10⁶ Am^-2 at $\text{3}\text{4}\text{H}{}_{\mathrm{c}}$), but are of the same order that one might expect in a low κ type II superconductor with similar pinning, and that the critical current density is directly proportional to the density of pinning centres in the material, surface currents playing no important role.