Search for penetration effects in the internal conversion of transitions in ¹⁶⁹Tm and ¹⁷¹Tm

Abstract

The K- and L-subshell internal-conversion coefficients of the transitions in ¹⁶⁹Tm populated in the decay of ¹⁶⁹Yb have been measured using a double-focusing electron spectrometer and a Ge(Li) γ-ray spectrometer, with special reference to the retarded transitions, in order to look for any nuclear-structure effects. The particle parameters of the K conversion electrons of the 198.0-, 177.2-, and 130.5-keV transitions in ¹⁶⁹Tm and the 308.2- and 295.6-keV transitions in ¹⁷¹Tm have been determined from e^--γ and γ-γ angular-correlation measurements using a single-gap electron spectrometer and NaI(Tl) and Ge(Li) γ spectrometers. A value of the penetration parameter γ=6-9 for the 198.0-keV transition in ¹⁶⁹Tm has been deduced from the conversion coefficients and the particle parameter. The upper limit of the penetration parameter for the 177.2-keV transition is λ≤7 from the present measurements. The conversion coefficients and particle parameters of the other transitions in ¹⁶⁹Tm and ¹⁷¹Tm measured in the present work agree within experimental errors with the theoretical values with no penetration effect. The M3 transition from the 316.2-keV level to the ground state in ¹⁶⁹Tm has been found to be retarded by a factor of 90±25 with respect to the singleparticle estimate.