THERMAL NUCLEATION OF THE NORMAL-STATE IN SUPERHEATED SUPERCONDUCTINGTIN GRAINS

Suspensions of superheated type-I superconducting Sn microspheres of 1 6-25 and 10-25 mu m diameters were irradiated at temperatures below 1 K and above 2 K by decay electrons from C-14 and S-35, respectively. M easurements of the radiation-induced gaps in the superheating transiti on curves indicate a full heating of the smallest grain volume of each suspension, contrary to a partial heating model based on the differen ce between quasiparticle relaxation and diffusion rates in Sn. The pho nons are in thermal equilibrium with the quasiparticles when the norma l state is nucleated.