Precise test of internal-conversion theory: Transitions measured in five nuclei spanning 50≤Z≤78

• Five internal conversion coefficients (ICCs) have been measured to better than ±2%.
• Transitions were selected to be sensitive to the assumptions used in ICC calculations.
• Results establish that the atomic vacancy must be accounted for in ICC calculations.

In a research program aimed at testing calculated internal-conversion coefficients (ICCs), we have made precise measurements of αK values for transitions in five nuclei, 197Pt, 193Ir, 137Ba, 134Cs and 119Sn, which span a wide range of A and Z values. In all cases, the results strongly favor calculations in which the final-state electron wave function has been computed using a potential that includes the atomic vacancy created by the internal-conversion process.