Speaker
Dr
Makito Oi
(Department of Physics, University of Surrey)
Description
Superdeformed states have been populated exclusively with the
fusion-evaporation reactions, which is suitable for a productin
of very high-spin states. This is possible through neutron evapolations
that do not take angular momentum away from the system.
However, as a consequence, such a high-spin states can be produced
only for neutron-deficient systems.
A $N=Z$ nucleus near the magic numbers, such as $^{40}$Ca,
has its ground state with a spherical shape.
The Fermi levels sit in the last orbit of the so-called sd-shell, and
most of the single-particle levels inside the sd-shell are filled.
Hence, any excited states of this nucleus need to cross the shell gap
beyond the sd-shell. But, once the gap is broken, substantial amounts
of single-particle orbitals are available in the fp-shell, enabling
strong collectivity. Consequently
and surprisingly, this double-magic nucleus shows a contrasting deformation
to the ground-state shape: neutron-richest superdeformation (so far)
with $\beta\simeq 0.6$ identified by Ideguchi et al. in 2001 [1].
Prior to the one in $^{40}$Ca,
a similar superdeformed structure was found in $^{36}$Ar [2].
A theoretical analysis based on the cranked Nilsson model predicts
quickly growing triaxial deformation of the superdeformed state
as the total angular momentum increases. The result was interpreted
as the band termination caused by the full alignments of the
the active valence orbitals. However, it is known that
the rotational alignment is strongly influenced
by the pairing correlation, which acts against
the Coriolis force. Therefore, it is important to check the pairing effect
to the band termination process.
Such an investigation is possible with
the Hartree-Fock-Bogoliubov method. Through
numerical calcluations the pairing effect is studied in terms of
how the band termination process is influenced.
In my talk, the details of my analysis will be presented.
[1] E. Ideguchi, et al., Phys. Rev. Lett. 87, 222501 (2001).
[2] C. E. Sevensson, et al., Phys. Rev. Lett. 85, 2693 (2000).
Primary author
Dr
Makito Oi
(Department of Physics, University of Surrey)
