Abstract
Long-lived isomeric states in 97Ag and 101−109In were investigated with the FRS Ion Catcher at GSI. In the isotope 97Ag, a long-lived (1/2−) isomeric state was discovered, and its excitation energy was determined to be 618(38) keV. This is simultaneously the first discovery of a nuclear isomeric state by multiple-reflection time-of-flight mass spectrometry. The measured excitation energies were compared to large-scale shell-model calculations, which indicated the importance of core excitation around 100Sn. Furthermore, advanced mean-field calculations for the 97Ag nucleus and relevant neighboring nuclei were performed, which have contributed to a better understanding of the repetitive appearance of certain isomeric structures in neighboring nuclei, and which have supported the discovery of the isomeric state in 97Ag in a global shell-evolution scheme.
Highlights
The lifetimes of isomers are much longer than those of common excited states [1]
The FRS Ion Catcher consists of three main parts: (i) the gas-filled cryogenic stopping cell (CSC) [27,28,29,30], which executes the complete slowing-down of the exotic nuclei produced at relativistic energies, (ii) a radio frequency quadrupole (RFQ) beamline [30,31,32,33], which is used for mass-selective transport and differential pumping, and (iii) the MR-TOF-MS [23,34,35], which performs direct mass measurements
The ground and isomeric states were fitted with a so-called double hyper-EMG [44] with one exponential tail on both sides
Summary
The lifetimes of isomers are much longer than those of common excited states [1]. There are several reasons for this: the shape, the spin, or the spin orientation relative to a symmetry axis of the isomeric state. The first discovery of a nuclear isomeric state by multiple-reflection time-of-flight mass spectrometry is presented in this paper. The multiple-reflection time-of-flight mass spectrometer (MR-TOF-MS) of the FRS Ion Catcher [23] is, due to its unique combination of performance parameters, an ideal device for the search for new isomeric states [24]. It combines a high mass resolving power (m/ m > 600, 000), short measurement time (> 0.01 s), high accuracy (relative mass accuracy of < 10−7), and non-scanning operation. The MR-TOF-MS of the FRS Ion Catcher has a high discovery potential for isomeric states with half-lives as low as the ms region
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