A Counter with Selective Efficiency for Recording the Recoilless γ-Rays of Sn119

A detector which has selective efficiency for the 23.8-keV γ-rays emitted without recoil from Sn119 is proposed and tested. The principle of its operation is based on the recording of internal-conversion electrons emitted by resonance-excited nuclei in a tin compound which has been placed within a Geiger counter.