Resonance Absorption of Gamma Rays in Normal and Superconducting Tin

A study of the resonant absorption of the 23.8-keV gamma rays in ${\mathrm{Sn}}^{119}$ has been made between 373 and 1.1°K by using the ${\mathrm{Sb}}^{119}$ $K$-capture parent. The source was prepared by bombarding natural Sn with 10-MeV deuterons in a cyclotron, and was thick enough to absorb resonantly a large portion of the recoilless photons emitted. By studying the self-absorption in this source between 373 and 60°K and taking into account the contributions to the intensity due to resonant scattering, an average value of the Debye temperature $\theta$ has been derived. In order to see if the phonon spectrum undergoes a change in passing from the superconducting to the normal phase, the counting rate was measured at several temperatures between 4.2 and 1.1°K, with and without a magnetic field strong enough to destroy the superconductivity of the source. Using the derived value of 140°K for $\theta$, it was concluded that the change in $\theta$ between the two phases could not be more than 0.76°K.