Measurement of the lifetimes of excited states in neutron-rich Ce isotopes
Neutron-rich cerium isotopes are located in the region of the nuclear chart some neutrons and protons above the doubly-magic ${}^{132}$Sn, where a variety of shape phenomena are expected. Among them, the evolution of the quadrupole collectivity going away from the shell closures, or the octup...
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| Format: | Others |
| Language: | en |
| Published: |
2018
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| Online Access: | http://tuprints.ulb.tu-darmstadt.de/7818/13/Dissertation_Guillermo_Fernandez_Martinez.pdf Fernández Martínez, Guillermo <http://tuprints.ulb.tu-darmstadt.de/view/person/Fern=E1ndez_Mart=EDnez=3AGuillermo=3A=3A.html> : Measurement of the lifetimes of excited states in neutron-rich Ce isotopes. Technische Universität, Darmstadt [Ph.D. Thesis], (2018) |
| Summary: | Neutron-rich cerium isotopes are located in the region of the nuclear chart
some neutrons and protons above the doubly-magic ${}^{132}$Sn, where
a variety of shape phenomena are expected. Among them, the evolution
of the quadrupole collectivity going away from the shell closures, or
the octupole deformation in the vicinity of $Z=56$ and $N=88$ stand out.
The goal of the present work is, hence, the study of the structural evolution
of neutron-rich cerium isotopes, through the knowledge of the reduced
transition strengths between their low-lying excited states. These
values have been derived from the direct measurement of the lifetimes of
excited states.
The fast-timing experimental campaign was carried out at the
Argonne National Laboratory, where a large variety of nuclei was produced
in the spontaneous fission of ${}^{252}$Cf. In order to ensure the
selection of the cerium isotopes of interest, one hemisphere of the
Gammasphere array, consisting of 51 high-resolution HPGe detectors,
was used. Additionally, 25 ultra-fast LaBr$_3$(Ce) detectors from the NuSTAR-FATIMA
collaboration allowed to measure the
lifetimes of the excited states of these selected isotopes
by means of the Generalised Centroid Difference Method. The use of such a large
combined array of HPGe and LaBr$_3$(Ce) detectors
is unprecedented in a fast-timing experiment.
Several lifetimes of low-lying excited states in the even-even
${}^{146-150}$Ce isotopes have been obtained, four of them for the first time.
The observed trend of the reduced transition strengths along the isotopic
chain, together with the systematics of the excitation energies confirm
the increasing collectivity towards more prolate shapes.
These experimental results have been compared to new theoretical calculations
obtained within the Symmetry Conserving Configuration Mixing and Shell Model
approaches. Both theoretical predictions seem to properly reproduce the
experimental results. |
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