The L-subshell conversion line intensity ratios of five pure M1 transitions have been measured with the Chalk River iron-free, π√2 β-spectrometer at momentum resolutions ranging from ≈ 0.04% to 0.19%. The transition energies in keV and the LI/LII and LI/LIII ratios for the cases studied are 144Pr, 80.12, 12.2 ± 0.3, 59.6 ± 3.0; 144Pr, 133.53, 13.4 ± 0.2, 64.3 ± 1.7; 166Ho, 82.45, 11.4 ± 0.2, 72.3 ± 1.1; 210Bi, 46.503, 9.67 ± 0.13, 115 ± 3; 212Bi, 238.6, 9.36 ± 0.13, 133.5 ± 6. The results have been compared with theoretical ratios deduced from the tabulations of Rose, Sliv and Band, Pauli, and Hager and Seltzer. These comparisons reveal significant discrepancies between the theoretical ratios of Rose and experiment for these M1 transitions. The theoretical ratios of Sliv and Band, Pauli, and Hager and Seltzer agree well among themselves and with experiment. The experimental ratios are found to be in best agreement with the theoretical ratios of Sliv and Band and of Pauli which take account of the contribution of the dynamic nuclear penetration effect to the internal conversion coefficient, but the experimental accuracies, which range from 2-4%, are not sufficient to allow an unqualified conclusion concerning the validity of this small correction. The L-subshell conversion ratios of the 59.03 keV, pure M3 (3- → 0-) transtion in 144Pr were also measured (see appendix) and found to be LI/LII = 6.43 ± 0.32 andLI/LIII = 0.662 ± 0.008. These ratios are in agreement with theory. © 1969.
