Measurements of conversion coefficients for transitions in 154Gd, 160Dy, 170Yb, 171Yb and 141Pr

Abstract

Internal conversion coefficients were measured by observing with a well-type NaI(Tl) crystal the photon spectra emitted during the de-excitation from the first excited state to the ground state of 154Gd, 160Dy, 170Yb, 171Yb and 141Pr. The results were obtained by analysis of either the singles spectra, or spectra obtained by coincidence-sum techniques, or both. For the coincidence work gating was done either with high-energy gamma rays or with beta particles. The spectra from the Yb isotopes were analysed on a computer using a least-squares, curve-fitting program. The photon detection efficiencies were calculated with a computer by performing numerical integrations. The K-shell internal conversion coefficients directly measured were 0.632±0.016 for 154 Gd, 1.47±0.05 for 170 Yb, 6.9±1.0 for 171 Yb and 0.375±0.009 for 141 Pr . The total internal conversion coefficients directly measured were 1.20±0.02 for 154 Gd and 4.52±0.11 for 160 Dy , which yield respective K-shell internal conversion coefficients of 0.637±0.016 and 1.54±0.06 when multiplied by K to total ratios. In order to eliminate interpolation errors from the internal conversion coefficient tables, theoretical values were obtained with computer calculations (point nucleus, no screening) normalized, by use of an effective nuclear charge, to the tables of Rose and Sliv and Band. The results for the transitions in 154Gd, 160Dy and 141Pr are in good agreement with theory. The ratio of the experimental result to the theoretical value is 1.06±0.05 for the transition in 170Yb. The result for the transition in 171Yb implies a mixing ratio of E2/M1 = 0.45±0.08, assuming the theoretical internal conversion coefficients are correct.