Speaker
Description
Nuclei with a large N/Z ratio are of great interest to test nuclear models and provide information about single particle states far off stability. During the last two decades there has been a substantial effort directed to gathering information about the region around the neutron-rich $^{132}$Sn [1-3]. Lifetimes of excited states provide direct access to the reduced transition probabilities of $\gamma$ transitions, which play an important role in the investigation of nuclear structure and the nucleon-nucleon effective interaction. The information available for the tin isotopes around $^{132}$Sn is scarce.
The excited structure of $^{131}$Sn was investigated in detail at the ISOLDE facility at CERN. We profited from the selective ionization by the ISOLDE Resonance Ionization Laser Ion Source (RILIS) [4] to enhance the production of each particular isomer in $^{131}$In, and study its decay separately for the first time. This measurement took place at the new ISOLDE Decay Station (IDS), equipped with four highly efficient clover-type Ge detectors, along with a compact fast-timing setup consisting of two LaBr$_3$(Ce) detectors and a fast $\beta$-plastic detector [5-8].
In this contribution we will report on the first measurement of subnanosecond lifetimes in $^{131}$Sn. A noticeable short half-life was derived for the the $\nu 3s^{-1}_{1/2}$ single-hole state, indicating an enhanced l -forbidden M1 behaviour for the $\nu 3s^{-1}_{1/2} \to \nu 3d^{-1}_{3/2}$ transition [9-11]. The measured half-lives of high-energy states, provided valuable information on transition rates, supporting the interpretation of these levels as core-excited states. In the other hand, the unambiguous separation of the decay provided an unique opportunity to disentangle the decay scheme of each $^{131}$In isomer. The extended level-schemes, the position of the $\nu 1h^{-1}_{11/2}$ single-hole state [12], as well as the observed correlation between n/$\gamma$ competition above the neutron-separation energy and the parent populating indium state will be discussed. Additionally, a revision of $\beta$-decay properties, such as log ft of the first-forbidden single-particle transitions, half-lives and P$_n$ values for the three $^{131}$In $\beta$-decaying states will be addressed.
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[12] B. Fogelberg et al., Phys. Rev. C 70, 034312 (2004).
