The ground states of /sup 176-86/Pt: an example of a shell model intruder state configuration

The systematics of excited states in the neutron-deficient even-mass Pt isotopes are shown to provide evidence that a strongly deformed configuration is present in the ground states of these isotopes. This configuration is proposed to be due to ( pi h/sub 9/2/)/sup 2/, based on proton intruder state systematics and the importance of valence neutrons and protons in producing deformation. It is suggested that this phenomenon is unprecedented and, for the present, unique to the neutron-deficient even-mass Pt isotopes. A simple test of this picture using the blocking effect of an h/sub 9/2/ proton coupled to the /sup 186/Pt core, as observed in /sup 187/Au, is discussed. The consequences of this intruder state structure in the neutron-deficient Pt isotopes on other observable quantities in this region are considered. (29 refs).