Lifetime of the first excited 2+ state in 172W and 178W

The lifetime of the first excited 2+ state in 172W and 178W has been measured in fast timing experiments using the Cologne Double Orange Spectrometer for conversion electron spectroscopy. The values of the isotopes 170–178W are compared to calculations in the Interacting Boson Model (IBM) employing the consistent Q formalism. An analysis of the B(E2) value systematics in the rare earth nuclei around mass A=170 using the NpNn-scheme shows signatures of a structural change in the tungsten isotopes which is not reflected in the energy systematics.