Speaker
Prof.
Tadashi Shimoda
(Department of Physics, Osaka University)
Description
Evolution of shell structures in a wide range of nuclear
chart is one of the most important subjects in nuclear
physics. In particular, breakdown of the $N=20$ shell
closure and onset of collectivity as increasing neutron
number in neutron-rich nuclei in the region of so-called
``island of inversion". In spite of intensive investigations
for many years, little is known on the spin-parity of
the levels in neutron-rich Mg isotopes. This situation has
been preventing quantitative understanding of their
structures.
\par
We have started systematic studies of neutron-rich Mg
isotopes by using an effective method to assign spin-parity
of their excited states. The essential is a use of
spin-polarized Na isotopes. The allowed $\beta$-decay asymmetry,
which strongly depends on the spins of the initial and final
states, determines unambiguously the spins of the daughter
states. The first application of this method was successfully
made for the $\beta$-delayed neutron-$\gamma$ spectroscopy
of polarized $^{11}$Li at the state-of-the-art ISOL-based
radioactive nuclear beam facility ISAC of TRIUMF, which
provides highly polarized alkali beams.
Detailed analyses enabled firm spin-parity assignments of
six levels in $^{11}$Be for the first time \cite{Hirayama05}.
\par
As the first step of the systematic studies on Mg isotopes,
$\beta$-delayed $\gamma$-decays from polarized $^{28}$Na
and $^{29}$Na have been observed in November 2007.
Preliminary analyses suggested that a new level and a revised
spin assignment for $^{28}$Mg and determined spin-parity of
two levels in $^{29}$Mg for the first time.
\par
The results will be presented and comparison with shell model
predictions will be discussed.
Primary author
Prof.
Tadashi Shimoda
(Department of Physics, Osaka University)
Co-authors
Anna Takashima
(Department of Physics, Osaka University)
Atsuko Odahara
(Department of Physics, Osaka University)
Hiroari Miyatake
(KEK)
Ken-ichiro Kura
(Department of Physics, Osaka University)
Kunihiko Tajiri
(Department of Physics, Osaka University)
Masaki Suga
(Department of Physics, Osaka University)
Masayuki Kazato
(Department of Physics, Osaka University)
Matthew Pearson
(TRIUMF)
Nobuaki Imai
(KEK)
Peter Jackson
(TRIUMF)
Phil Levy
(TRIUMF)
Tomokazu Suzuki
(Department of Physics, Osaka University)
Tomonori Fukuchi
(RIKEN)
Toshikazu Hori
(Department of Physics, Osaka University)
Toshiyuki Masue
(Department of Physics, Osaka University)
Yoshikazu Hirayama
(KEK)
