Precise tests of internal-conversion theory

Using the 165.9-keV M1 transition in 139La as a calibrant, we have determined the K-shell internal conversion coefficients (ICCs) for the 127.5-keV E3 transition in 134Cs and the 661.7-keV M4 transition in 137Ba to 0.6% precision. Unlike previous less-precise measurements of these ICCs, which differed significantly from calculated values, our results agree well with calculations that include the atomic K-shell vacancy and disagree with those that exclude it. These results, which are consistent with what we also found for 193Ir, confirm our earlier conclusions but for different energies, multipolarities and atomic numbers.