Search for penetration effects in the internal conversion of transitions in <SUP>169</SUP>Tm and <SUP>171</SUP>Tm

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) &#947;-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--&#947; and &#947;-&#947; angular-correlation measurements using a single-gap electron spectrometer and NaI(Tl) and Ge(Li) &#947; spectrometers. A value of the penetration parameter &#947;=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 &#955;&#8804;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&#177;25 with respect to the singleparticle estimate