Speaker
Description
The neutron-rich $^{144-146}$Ba isotopes have been studied recently in terms
of their experimental B(E3) values [1,2]. Although featuring large uncertainties,
the results were found to be significantly larger than any theoretical calculation.
Similar questions exist for the slightly lighter isotope $^{140}$Ba, which is particularly
interesting since it is located at the onset of octupole correlations. The lifetimes
of the lower lying states are completely unknown, with the sole exception of the first
2$^+$ state [3].
In this work, we report on the outcome of a short test run, attempting to populate
the states of interest by the $^{138}$Ba($^{18}$O,$^{16}$O)$^{140}$Ba reaction. The experiment was carried
out at IFIN-HH using a specially manufactured natBa target sandwiched between two Au layers.
This was considered imperative due to barium’s quick oxidation. Four energies
(61,63,65,67 MeV) below the Coulomb barrier have been tested. The subsequent γ-decay
was measured using the Bucharest ROSPHERE array, consisting of 15 Ge detectors and
10 LaBr$_3$(Ce) scintillators.
The preliminary results from the test run report on the level population strengths and
the limits in lifetime measurements. A new run has been approved to complete the measurements
of the lifetimes in the ground state band of $^{140}$Ba, which are expected to provide
new information on the structural effects in neutron-rich barium isotopes, especially
regarding quadrupole and octupole degrees of freedom. The findings are also expected
to act as stringent tests to theoretical modeling in this mass regime.
[1] B. Bucher et al., PRL 116, 112503 (2016)
[2] B. Bucher et al., PRL 118, 152504 (2017)
[3] C. Bauer et al., PRC 86, 034310 (2012)
