Abstract
The level structures of the very neutron-rich nuclei 128Pd82 and 126Pd80 have been investigated for the first time. A new isomer with a half-life of 5.8(8) μs in 128Pd is proposed to have a spin and parity of 8+ and is associated with a maximally aligned configuration arising from the g9/2Pd proton subshell with seniority υ = 2. The level sequence below the 8+ isomer is similar to that in the N = 82 isotone 130Cd, but the electric quadrupole transition that depopulates the 8+ isomer is more hindered in 128Pd than in 130Cd, as expected in the seniority scheme for a semi-magic, spherical nucleus. For 126Pd, three new isomers with Jπ = (5-), (7-), and (10+) have been identified with half-lives of 0.33(4) μs, 0.44(3) μs, and 23.0(8) ms, respectively. The smaller energy difference between the 10+ and 7- isomers in 126Pd than in the heavier N = 80 isotones can be interpreted as being ascribed to the monopole shift of the h11/2 neutron orbit. The nature of the N = 82 shell closure scrutinized with these characteristic isomers is discussed.
Highlights
The concept of magicity is of supreme importance for many-body fermionic systems in a confined space
The stability of atomic nuclei, which consist of a number of sub-atomic particles called protons and neutrons, is much influenced by a shell structure and its resulting magic numbers; nuclei with specific numbers of nucleons (2, 8, 20, 28, 50, 82 both for protons and for neutrons, and 126 for neutrons) near the β-stability line necessitate relatively high energies to remove one or two nucleons compared to the neighboring isotopes
For the last few decades, the study of exotic nuclei using radioactive isotope (RI) beams revealed that the aforementioned magic numbers are not necessarily universal and are subjected to a change in some regions of light-mass nuclei with highly unbalanced ratios of protons and neutrons [1, 2]
Summary
The concept of magicity is of supreme importance for many-body fermionic systems in a confined space. The nature of the N = 82 shell closure will be discussed in terms of the seniority isomerism in the N = 82 isotones, as well as the effect of the monopole interaction between the g9/2 proton and h11/2 neutron subshells.
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