16+Spin-Gap Isomer inCd96

Abstract

A -decaying high-spin isomer in 96 Cd, with a half-life T 1=2 ¼ 0:29 þ0:11 À0:10 s, has been established in a stopped beam rare isotope spectroscopic investigations at GSI (RISING) experiment. The nuclei were produced using the fragmentation of a primary beam of 124 Xe on a 9 Be target. From the half-life and the observed decays in the daughter nucleus, 96 Ag, we conclude that the -decaying state is the long predicted 16 þ ''spin-gap'' isomer. Shell-model calculations, using the Gross-Frenkel interaction and the ðp 1=2 ; g 9=2 Þ model space, show that the isoscalar component of the neutron-proton interaction is essential to explain the origin of the isomer. Core excitations across the N ¼ Z ¼ 50 gaps and the Gamow-Teller strength, BðGTÞ distributions have been studied via large-scale shell-model calculations using the ðg; d; sÞ model space to compare with the experimental BðGTÞ value obtained from the half-life of the isomer. DOI: 10.1103/PhysRevLett.107.172502 PACS numbers: 21.60.Cs, 23.20.Lv, 23.35.+g, 26.20.Àf The nuclear landscape around the heaviest known bound doubly magic self-conjugate nucleus 100 Sn, which resides far from the valley of stability, exhibits a rich variety of nuclear structure phenomena [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. A feature of great interest in this region is the presence of isomeric states, especially those which may undergo particle decay. Indeed, early work by Peker et al. was paramount in motivating studies of such states based on three or four particle/hole configurations in nuclei. This included the 16 þ isomeric state in 96 Cd, which was suggested to result from a four-hole configuration relative to a 100 Sn core that may decay via proton radioactivity [1].A particularly interesting issue in this region is the role played by the neutron-proton, np, interaction in leading to the existence of the isomers. The isovector (T ¼ 1) component of the interaction between like-nucleons is known to dominate in all non-self-conjugate nuclei while the T ¼ 1 np interaction has been shown to have a major influence on the N ¼ Z line below mass 80 due to the large overlap of the proton and neutron wave functions [16]. Although calculations suggest an important influence of the isoscalar (T ¼ 0) np interaction on the structure of medium-heavy N ¼ Z nuclei, its role has been less clear and often debated [17][18][19][20]. Very recent experimental work has claimed the first indications for the crucial role of this interaction at low spins in 92 Pd, that are supported by shell-model (SM) calculations [2]. In order to establish or dispute the expected strong influence of the T ¼ 0 np interaction for self-conjugate nuclei close to 100 Sn, it is of paramount importance to obtain further evidence for its effects.Long standing SM calculations for the self-conjugate nucleus 96 Cd predict the presence of a 16 þ state at an energy lower than that of the first 12 þ and 14 þ states [10]. This situation arises from the strong influence of the T ¼ 0 np interaction and results in ''spin-...

New and comprehensive β - and βp -decay spectroscopy results in the vicinity of Sn100

“…22. The delayed γ rays belonged to the decay cascade of the (15 + ) isomer in 96 Ag [18], populated by the GT decay of the 16 + isomer 96m Cd [5]. Several prompt γ rays were observed for the first time at 489, 843, 3178, and 3691 keV, in addition to the previously known 421-keV transition.…”

“…These nuclei are bound against proton emission by only a few MeV, and experimentally observable quantities such as excitation energies (E x ), Gamow-Teller (GT) decay strengths B GT , and electromagnetic (EM) transition strengths are used to assess quantitatively the robustness of the 100 Sn core. Previous experiments on these nuclei have yielded insightful and/or controversial results [2][3][4][5], highlighted by the GT decay of 100 Sn with the smallest log f t value of all known β decays [6]. In the context of nuclear astrophysics, experimental half-lives (T 1/2 ) and β-delayed proton branching ratios (b β p ) are needed for reaction flow calculations of the rapid-proton (r p) capture process of nucleosynthesis via type I x-ray bursts and steadystate burning [7][8][9].…”

“…Various types of shell model (SM) calculations have been performed to describe the nuclear properties of isotopes near the N = Z = 50 double shell closure: empirical shell models (ESMs) [11][12][13][14][15] in the proton (π ) and neutron (ν) model space of p 1/2 and g 9/2 orbitals above the 76 Sr core; and largescale shell model (LSSM) calculations involving higher-lying orbitals above the 100 Sn core [5,6,[16][17][18]. They have been adopted and tuned to reproduce the energies and EM transition strengths of core-excited states in this region [18][19][20][21][22].…”

Recoil-βtagging study of theN=Znucleus66As

“…This may lead to enhanced np pairing correlations in the isoscalar T = 0 channel. However, for medium-mass N = Z nuclei there is no clear evidence of the strong T = 0, np correlations until the A ∼ 90 mass region is reached [1][2][3].…”

β decays of the heaviest N=Z−1 nuclei and proton instability of In97

“…The heaviest N = Z doubly magic 100 Sn and atomic nuclei in its vicinity have been actively investigated both theoretically and experimentally [1], because several important topics in nuclear structure and astrophysics converge in this region of the chart of nuclides. Significant efforts have been made to address questions concerning the robustness of the N = Z = 50 shells and evolution of single-particle energies [2][3][4][5][6][7][8], the effect of proton-neutron (pn) isoscalar/isovector interactions in heavy N ∼ Z nuclei [9,10], and the location of the proton drip line. The most notable results were reported along the N = Z line [11][12][13], where the production rates of such exotic radioactive isotopes were at the lowest allowed limit.…”