Ponente
Descripción
The isotopic chains close to the nuclei number $Z$=50 have motivated extensive experimental and theoretical efforts during the last decades. Their structure provide an excellent ground to study shell-evolution along the chain and to investigate the interplay between single-particle and collective degrees of freedom. The systematic study of excited structure of nuclei in the double magic $^{132}$Sn region, and specifically the measurement of excited-state lifetimes, provides key observables to get a deeper insight on nuclear structure.
A new experimental camping was carried out at the ISOLDE facility to study the $\beta$-decay of neutron-rich cadmium isotopes. High intensity Cd (Z=48) beams were produced after the fission of a thick UC$_{x}$ target, selectively ionized by the ISOLDE Resonance Ionization Laser Ion Source (RILIS) and separated in mass using the General Purpose Separator (GPS) ISOLDE mass separator. A temperature-controlled quartz transfer line was used to ensure purity of the cadmiun beams.
In this contribution results derived for the A=128 isobaric chain will be discussed [3-5]. Our experiment exploited the excellent spectroscopic capabilities provided by the ISOLDE Decay Station (IDS). The fast-timing configuration was employed, which includes 6 highly efficient clover-type HPGe detectors, altogether with two LaBr$_3$(Ce) and three ultrafast $\beta$-plastic detectors arranged in a close geometry. This configuration is well suited to measure lifetimes of excited states down to the 10 ps via ultra-fast timing methods [1,2].
The excited structure of $^{128}$In was populated via the $\beta$-decay of the $^{128}$Cd 0$^{+}$ ground state. In the case of $^{128}$Sn, the excited levels were selectively fed only by the $\beta$-decay of the precursor $^{128}$In (3)$^{+}$ ground state, excluding the contribution of others $\beta$-decaying states due to selection rules imposed by the parent $^{128}$Cd 0$^{+}$ state. In this contribution, we will inform on the the expanded level-schemes for both $^{128}$In and $^{128}$Sn. Additionally, we will report on the first direct measurements lifetimes below the nanosecond range in both nucleus. A discussion will be provided on the derived $B(XL)$ transition rates are discussed, and particularly on the lifetime of the first 4$^+$ stat in $^{128}$Sn and the derived $B(E2;4^+\to2^+)$.
