β-delayed proton decay of a high-spin isomer inA94g

Abstract

The decay of the ͑7 + ͒ and ͑21 + ͒ isomers of the N = Z isotope 94 Ag was studied at the GSI on-line mass separator by measuring ␤-delayed protons, ␥ rays, proton-␥ and proton-␥-␥ coincidences as well as the ␤-strength distribution. We have observed high-spin (up to 39/ 2) states in 93 Rh populated by proton emission following the ␤ decay of the 94 Ag isomers. The major part of the population is related to the ␤ decay of the known ͑7 + ͒ isomer whose half-life is 0.61͑2͒ s. The assignment of the high-spin ͑21 + ͒ isomer in 94 Ag with a half-life of 0.39͑4͒ s has been confirmed. The excitation energy and ␤-decay energy of the ͑21 + ͒ isomer were measured to be at least 5.4 and 17.7 MeV, respectively. At this excitation energy, the ͑21 + ͒ isomer is expected to be unbound to direct one-proton, two-proton, or ␣ decays. The remarkably long half-life of the ͑21 + ͒ isomer with the highest spin and excitation energy ever observed for ␤-decaying nuclei makes a new textbook example of a nuclear high-spin trap. The branching ratios for ␤-delayed proton emission are about 20% and 27% for the decays of the ͑7 + ͒ and ͑21 + ͒ isomers, respectively. The properties of the experimentally identified 93 Rh levels are discussed in comparison to shell-model predictions.

Structure of upper-g9/2-shell nuclei and shape effect in theAg94

“…Because of the recent experimental successes, the highspin I π = 21 + and low-spin 7 + isomers in the odd-odd N = Z nucleus 94 Ag have become a discussion focus [8,9,10,11]. In this nucleus, the high-spin 21 + isomer has a high excitation energy of 6.7 (5) MeV with a notably long half-life of 0.39(4) s, and is open to β, one-proton, and two-proton decays [12,13].…”

“…In this nucleus, the high-spin 21 + isomer has a high excitation energy of 6.7 (5) MeV with a notably long half-life of 0.39(4) s, and is open to β, one-proton, and two-proton decays [12,13]. Although the shell model calculations with the empirical effective interaction in the restricted (1p 1/2 , 0g 9/2 ) model space could reproduce the energy levels and high-spin isomers in 95 Ag, 95 Pd, and 94 Pd, it failed to predict the isomerism of 21 + state in 94 Ag [9,10]. On the other hand, it has been shown that the large-scale shell model calculations with the extended model space (0g 9/2 , 1d 5/2 , 0g 7/2 , 1d 3/2 , 2s 1/2 ) can obtain a 21 + -19 + level inversion, which suggests that the core excitations across the 100 Sn shell-closure play a crucial role in generating the 21 + isomer with such a long halflife [9].…”

Properties of γ -decaying isomers and isomeric ratios in the Sn100 region

“…Among the relevant topics are the robustness of the N = Z = 50 shell closures in 100 Sn and the superallowed Gamow-Teller decay [1]; the limit of bound N = Z heavy nuclei and the location of the proton dripline; the role of T = 0 proton-neutron (pn) interactions in contrast isomers in 94 Ag, 96 Cd, and 98 In [3,[13][14][15][16][17][18][19]; and core-excited isomers in 96 Ag and 98 Cd [20][21][22]. This is by no means an exhaustive list.…”

β-delayed proton emission in the100Sn region

“…[1][2][3][4][5][6]). The influence of the high-spin g 9/2 single-particle orbital on the valence nucleon or hole structure and the proton-neutron interactions enhanced in N ≈ Z nuclei [7], lead to a broad range of spin and seniority effects including isomers [8], which can be sensitive probes of nuclear structure.…”