Precise measurement of alpha(K) for the M4 transition from Ir-193(m): A test of internal-conversion theory

Abstract

The 10.5-day isomer in Ir-193 decays by a single 80.2-keV M4 transition directly to the ground state of that nucleus. We have measured the total intensity of K x rays relative to 80.2-keV gamma rays for this transition to be 98.7(6). With the K-shell fluorescent yield for iridium taken to be 0.958(4), this result yields alpha(K) = 103.0(8) for the K-shell internal conversion coefficient (ICC). The calculated alpha(K) for this transition is particularly sensitive to the treatment of the hole that is created by conversion in the atomic K shell. Recent ICC tables, which ignore the hole, yield alpha(K) = 92.0. We demonstrate that calculations incorporating the hole produce values between 99.6 and 103.3 depending on the approximation used. Our result strongly supports the need to include the hole.