Electron Capture ofYb169to Levels inTm169

The decay of ${\mathrm{Yb}}^{169}$ by electron capture has been studied with permanent magnet spectrographs and scintillation counter techniques. Multipolarities of all transitions (including mixing) have been deduced. A level scheme is proposed. Two metastable levels of 4×${10}^{-7\mathrm{}}$ and 4.5×${10}^{-8\mathrm{}}$ second have been found, in addition to the well-known 6.4×${10}^{-7\mathrm{}}$ sec level. These metastable levels are all depopulated by $D+Q$mixtures in which the dipole radiation is greatly retarded (by factors of ${10}^6$ to ${10}^8$) and the quadrupole radiation is retarded by factors of ${10}^2$ to ${10}^3$ as compared to the single-particle estimates. For certain transitions the corrections to the $M1\mathrm{}$ internal conversion coefficients (necessary because of finite nuclear size) have been obtained for the $K$, $L_{\mathrm{I}}$ and $L_{\mathrm{II}}$ shells. The screening correction for the $K-LL$ Auger lines has been obtained for this nucleus ($Z=69\mathrm{}$).