Speaker
Prof.
Yoshitaka Fujita
(Research Center for Nuclear Physics (Toyonaka), Osaka Univeristy)
Description
Isospin symmetry is based on the almost identical `behavior' of
proton and neutron in terms of the strong interaction.
However, due to isospin breaking interactions, including
electro-magnetic interaction, slight asymmetry is associated with
the nuclear structure of mirror nuclei.
We have been studying Tz=\pm 1-->0, Tz=\pm 3/2-->\pm 1/2, and
Tz=\pm 2-->\pm 1 mirror Gamow-Teller (GT) transitions as a tool to
study the nuclear structure of relevant nuclei in connection with
isospin symmetry and isospin selection rules.
The Tz=+1-->0, +3/2-->+1/2, and +2-->+1 GT- transitions have been
studied by high-resolution (about 30 keV) \beta- like (3He,t)
reactions performed at RCNP, Osaka, while mirror GT+ transitions,
in particular for lower Z, pf-shell nuclei, by the \beta+ decays
of proton rich unstable nuclei performed at GANIL, Caen and GSI,
Darmstadt.
Note that the production rate of the negative Tz nuclei in the
Z > 30 region is the largest at BigRIPS @RIKEN.
Since these nuclei are situated on the path of rapid-proton (rp)
process, decay study of them are also of astro-physical interest.
Eurica setup in combination with BigRIPS was used to study the
GT transitions (and also Fermi transitions) by the \beta decay of
Tz= -1, -3/2, and -2 nuclei in the higher Z, pf-shell region
(Z=30 - 36). The initial 345 MeV/nucleon 78Kr beam with an
intensity up to 300 pnA on the Be target was used for the
production of fragments.
It is expected that these near-drip-line nuclei decay with various
decay modes due to large decay Q-values. They can be delayed-
\gamma, delayed-proton, and even delayed-\gamma-proton.
Therefore, measurements of particle decay as well as gamma decay
are important.
Produced unstable nuclei were implanted in active stopper, i.e.,
WAS3ABi setup, for the measurement of \beta rays and delayed-
protons. The setup consists of three 1mm thick double-sided Si
strip detectors (DSSSD) with each of them having an active area
of 60 x 40 mm2 segmented into 60 vertical by 40 horizontal strips.
The WAS3ABi setup was surrounded by the EURICA setup consisting
of 12 HPGe CLUSTER-detectors of Euroball type for the efficient
measurement of \gamma rays.
Owing to the large productive power of unstable nuclei at BigRIPS,
we could observe Tz=-1 nuclei 58Zn, 60Ga, 62Ge, 64As, 66Se, and
70Kr, Tz=-3/2 nuclei 57Zn, 61Ge, 65Se, and 69Kr, Tz=-2 nuclei
60Ge and 64Se. It is decided that all of them will analyzed
inside our collaboration.
After performing particle identifications, we started to have
precise half-life values. For some of the nuclei, the error-bars
have reduced by one-order-of-magnitude due to the good statistics.
Reconstruction of \gamma-decay scheme has also started recently.
