Search for Penetration Effects in the Internal Conversion of Transitions in ${}_{}{}^{169}{}_{}{}^{}\mathrm{Tm}$ and ${}_{}{}^{171}{}_{}{}^{}\mathrm{Tm}$

The $K$- and $L$-subshell internal-conversion coefficients of the transitions in ${}_{}{}^{169}{}_{}{}^{}\mathrm{Tm}$ populated in the decay of ${}_{}{}^{169}{}_{}{}^{}\mathrm{Yb}$ have been measured using a double-focusing electron spectrometer and a Ge(Li) $\gamma$-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 ${}_{}{}^{169}{}_{}{}^{}\mathrm{Tm}$ and the 308.2- and 295.6-keV transitions in ${}_{}{}^{171}{}_{}{}^{}\mathrm{Tm}$ have been determined from $e^{-}-\gamma$ and $\gamma -\gamma$ angular-correlation measurements using a single-gap electron spectrometer and NaI(Tl) and Ge(Li) $\gamma$ spectrometers. A value of the penetration parameter $\lambda =6-9\mathrm{}$ for the 198.0-keV transition in ${}_{}{}^{169}{}_{}{}^{}\mathrm{Tm}$ 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 $\lambda \le 7$ from the present measurements. The conversion coefficients and particle parameters of the other transitions in ${}_{}{}^{169}{}_{}{}^{}\mathrm{Tm}$ and ${}_{}{}^{171}{}_{}{}^{}\mathrm{Tm}$ measured in the present work agree within experimental errors with the theoretical values with no penetration effect. The $M3\mathrm{}$ transition from the 316.2-keV level to the ground state in ${}_{}{}^{169}{}_{}{}^{}\mathrm{Tm}$ has been found to be retarded by a factor of 90 ± 25 with respect to the singleparticle estimate.