Loss of collectivity at high spin in 172W and a three-band interpretation of first yrast upbends.

A measurement of lifetimes in /sup 172/W by the Doppler-shift recoil-distance technique indicates a reduction of the transition quadrupole moments by about 15% for spins > or =12. This can be understood if the rotation-induced structure change is due not only to i-italic/sub 13/2/ neutrons, which is the standard theory for this region of nuclei, but also to h-italic/sub 9/2/ protons. The resulting three-band interpretation of the ''upbend'' in the yrast level sequence is supported by energy-level systematics suggesting that it is valid for a wide range of nuclei in this region.