Nuclear Seminar

Evidence of triaxial deformation in N=100 nuclei?

Dr. Daryl Hartley
Department of Physics, U.S. Naval Academy
Annapolis, Maryland

Monday, November 13, 2006   4:00 p.m.   NSH 124
(Refreshments served prior to seminar in NSH 124)

 

The verification of the nuclear wobbling motion in ¹⁶³Lu is perhaps the clearest experimental evidence of stable triaxial deformation in any nucleus.  Ultimate Cranker calculations suggested that the region of nuclei near Z = 72 and N = 94 was prone to this asymmetric shape if the nucleus could be excited into the second minimum.  Recently four strongly-deformed bands in ¹⁷⁴Hf (Z = 72, N = 102) were observed and similar Ultimate Cranker calculations suggested that such structures should be triaxial as well.  Indeed, a triaxial strongly deformed gap appears in the calculation at N =100 at large deformation (epsilon ~ 0.42).  Therefore, two experiments were performed in order to test this theory.  First, a search for linking transitions between the ¹⁷⁴Hf bands was performed which would help establish whether wobbling is occurring and thus confirm the asymmetric shape.  Although four new strongly-deformed bands were found in ¹⁷⁴Hf, there were no signs of these key linking transitions.  In addition, it became clear that the bands in ¹⁷⁴Hf were structurally different than those in ¹⁶³Lu that display wobbling.  A second experiment was then performed on ¹⁷¹Ta (Z = 73, N = 98), which is much more similar to ¹⁶³Lu than ¹⁷⁴Hf.  However, no wobbling was observed in this nucleus, and therefore we have not been able to conclusively prove that the region of triaxial strongly deformed bands extends out to the N = 100 nuclei.  The question has now arisen of whether wobbling will only be observed in Lu nuclei near N = 94, or can other nearby nuclei take on the unusual asymmetric shape.  These issues will be discussed and will open a dialogue for a possible explanation of the triaxial shapes in the rare-earth region.