Ⅱ-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 51 (2018)

γ-decaying isomers and isomeric ratios in the 100 Sn region†
J. Park,∗1,∗2 R. Krücken,∗1,∗2 D. Lubos,∗3,∗4,∗5 R. Gernhäuser,∗3 M. Lewitowicz,∗6 and S. Nishimura,∗4for the EURICA Collaboration
The structure of the heaviest N = Z doubly magic
nucleus 100 Sn and the nuclei in its vicinity has been
investigated in depth both experimentally and theoretically.1) Isomeric states in these exotic isotopes contain valuable experimental information on some of theresearch topics in this region of nuclides, such as therobustness of the N = Z = 50 shells and the role ofthe proton-neutron interaction in N ∼ Z nuclei.
This report contains a summary of results from theEURICA Xe campaign in 2013 on the γ-decaying isomers in the 100 Sn region. Proton-rich isotopes in 100 Sn
region were produced from fragmentation reactions of124
Xe on a 9 Be target, and were separated and identiﬁed through BigRIPS and the ZeroDegree spectrometer at the RIBF. They were implanted in WAS3ABi,2)
and time-delayed γ rays emitted from the isomers ofthe implanted nuclei were detected with EURICA3) for
half-life (T1/2 ) measurements.
Several new results were found: the discovery ofa (4+ ) isomer in 92 Rh; the excitation energy of the(15+ ) isomer in 96 Ag, and the T1/2 of the (6+ ) isomerin 98 Cd. Figure 1 shows the electromagnetic transition strengths derived from half-life measurements ofγ-decaying isomers observed in this experiment, as wellas the theoretical values from diﬀerent shell model(SM) calculations. The SLGM interaction4) uses amodel space of proton and neutron (2p1/2 , 1g9/2 ) orbitals above the 76 Sr core. The other SM approaches
are described in the original article. Two sets of proton and neutron eﬀective charges (a) and (b) were employed to gauge and account for core polarization effects. A good agreement between experimental andtheoretical transition strengths was found in general.
However, the transition strengths were signiﬁcantly
lower than predicted in 92,93 Ru. On the other hand,experimental transition strengths of the core-excited(12+ ) isomer in 98 Cd exceeding SM predictions may
be related to the increased proton core polarizationin light, even-mass Sn isotopes.5) Further theoreticaleﬀorts are needed to address these discrepancies.
In addition, experimental isomeric ratios of both γdecaying and β-decaying isomers were determined andcompared with the abrasion-ablation model6,7) coupled to the sharp cutoﬀ model. A good agreement
†∗1
∗2
∗3
∗4
∗5
∗6Nucleus, J πi → J fπ, σ l88

Zr, 8+ → 6+ E 290

Experiment
SLGM (a)SLGM (b)Other (a)Other (b)Nb, (11−) → (9−) E 290

Mo, 8+ → 6+ E 2
Mo, 8+ → 6+ E 292
92
92

Tc, (4+) → (6+) E 2
Ru, (8+) → (6+) E 2

92

Rh, (4+) → (2+) E 2

93

Ru, (21/2+) → (17/2+) E 2
94
Pd, (19−) → (16+) E 3
94

Pd, 14+ → 12+ E 2

96

Pd, (8+) → (6+) E 2
Ag, (19+) → (15+) E 4

9696

Ag, (19+) → (17+) E 2

96

Ag, (15+) → (13+) E 2
98
Ag, (4+) → (6+) E 298

Cd, (12+) → (8+) E 4
Cd, (12+) → (10+) E 29898

Cd, (8+) → (6+) E 2

98

Cd, (6+) → (4+) E 2

10−1
110
Transition strength (W.u.)

Fig. 1. Experimental electromagnetic transition strengthsof isomers measured in this work and shell model calculations. See the text for details on the diﬀerent models.

between experimental and theoretical values was obtained for positive-parity isomers with J > 4.
No experimental signature of an isomer in 100 Sn wasfound, which was hypothesized from SM.8,9) With assumptions from SM calculations and the theoreticalisomeric ratio, limits on the γ-ray energy and T1/2 wereproposed on the isomer in 100 Sn.
References

Condensed from the article in Phys. Rev. C. 96, 044311(2017)
Department of Physics and Astronomy, University of British
Columbia
TRIUMF
Physik Department, Technische Universität München
RIKEN Nishina Center
Excellence Cluster Universe, Technische Universität München
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