Physics and Astronomy Colloquium
		    Tuesday, March 26, 2002
	4:10 p.m., Room 118 Physics-Astronomy Building
		Refreshments served at 3:45 p.m.

     (An informal meeting for all students will be held from 
     3:15-3:45 outside Room 224 PA -- All students welcomed)

	Superdeformation in Nuclei: Order Embedded in Chaos

			 Teng Lek Khoo
		 Argonne National Laboratory

In nuclei, shell structure can lead to the creation of an excited
minimum, or false vacuum, characterized by large deformation (~2:1 axis
ratio).  Within this secondary minimum, there exist ordered states, with
good quantum numbers, even though they are embedded in a dense sea of
chaotic, highly excited states from the primary minimum. As the hot,
chaotic compound nucleus cools, a small fraction of gamma cascades
populates the superdeformed well, flowing through excited rotational
bands, which may be ergodic.  Trapped cascades reach the "ground" band
of the minimum, where cold ordered rotation gives rise to equi-spaced
sharp lines.  Tunneling out of the superdeformed well precipitates a
sudden decay out of the minimum, which is mediated by weak coupling
between ordered superdeformed and chaotic normal-deformed states.  The
decay spectrum has a statistical shape similar to that of
neutron-capture gamma rays.  Finally, the nucleus settles to the ground
state through gamma decays, which are governed by selection rules
imposed by conserved quantum numbers.  Hence, the "life" of  a
superdeformed nucleus reflects an unusual double cycle of chaos-to-order
transition.