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Internal conversion coefficients were measured by observing with a well-type Nal(Tl) crystal the photon spectra emitted during the de-excitation from the first excited state to the ground state of Gdl54,D)y 160, Ybl70, Ybl71 and Prl41 following the respective beta decays of Eul54, Tbl60, Tm170, Tml71 and Cel41. 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 analyzed on a computer using a least-squares curve-fitting program. The photon detection efficiencies, necessary for the measurements, were calculated with a computer by performing numerical integrations. The following K-shell internal conversion coefficients were measured directly for first excited state to ground state transitions: 0.632 ± 0.016, for Gdl54; 1.48 ± 0.05, for Ybl70; 6.9:1: 1.0, for Ybl71 and 0. 375 ± 0. 009, for Prl41. The total internal conversion coefficients were measured for the first excited state to ground state transitions in Gdl54 and nyl60 and found to be 1. 20 ± 0. 02 and 4. 52± 0. 11, 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. The results for these 2+->0+ transitions in Gdl54 and Dyl60 and for this -t -forbidden Ml transition in Prl41 are in good agreement with theory. The ratio of the experimental result to the theoretical value is 1. 09 ± 0. 06 for this 2+-0+ transition in Ybl 70. The result for this Ml + E2 transition in Ybl71 implies a mixing ratio of E2/Ml = 0. 45 :±. 0. 09, assuming the theoretical internal conversion coefficients are correct.

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