Ⅰ. HIGHLIGHTS OF THE YEARRIKEN Accel. Prog. Rep. 48 (2015)

1p3/2 Proton-Hole State in 132 Sn and Shell Structure Along N=82†
J. Taprogge,∗1,∗2,∗3 A. Jungclaus,∗1 H. Grawe,∗4 S. Nishimura,∗2 P. Doornenbal,∗2 G. Lorusso,∗2G.S. Simpson,∗5 P.-A. Söderström,∗2 T. Sumikama,∗6 Z.Y. Xu,∗7 H. Sakurai,∗2,∗7 H.Watanabe,∗2 on behalf of
the RIBF-85 and RIBF-60&62R1 collaborations
The nucleus 132 Sn is of particular interest for nuclear structure investigations since it is the only heavy
neutron-rich doubly-magic nucleus far away from thevalley of stability which is accessible for experimental studies. While 132 Sn as well as the neighboring
Sn (Z=50) and Sb (Z=51) isotopes have been studied in detail in the past, the experimental information
for nuclei in the region below 132 Sn is scarce. Important knowledge, e.g. with respect to the energies of theproton single-hole states in 132 Sn, is still missing.
In an experiment performed in December 2012 aspart of the EURICA campaign at the RadioactiveIsotope Beam Factory (RIBF), the neutron-rich nuclei 131,132 Cd were produced by the in-ﬂight ﬁssion ofa 238 U beam and implanted into the active stopper
WAS3ABi. The γ rays emitted following the β decay of 131 Cd and after β-delayed neutron emission of132
Cd were detected with the EURICA array comprising 84 germanium crystals. A single γ ray with anenergy of 988 keV was observed in the decays of both131
Cd and 132 Cd. It was placed to populate the known(1/2− ) β-decaying isomer in 131 In at an excitation energy of Ex = 365(8) keV thus deﬁning a second excitedstate at 1353 keV. This newly identiﬁed state is preliminary assigned to have spin and parity of 3/2− andto correspond to the previously unknown 1p3/2 proton
single-hole state with respect to the 132 Sn core. A fullaccount of the arguments which lead to this assignmentis presented in Ref. 2) .
Using the newly established 1p3/2 proton singlehole energy, shell-model calculations have been performed to calculate the energies of the ﬁrst excited
2+ states and the proton gaps ∆2p [deﬁned here as∆2p = M (Z + 2, N ) + M (Z − 2, N ) − 2M (Z, N ), withM (Z, N ) the mass of a nucleus with Z protons andN neutrons] for the N =82 isotones below 132 Sn asshown in Fig. 1. For comparison, Fig. 1 also shows theresults of similar SM calculations performed for theN =50 isotones below 100 Sn, in that case in comparison with available experimental information. Whilefor the N =50 isotonic chain typical signatures of subshell closures are observed at Z=38 and 403,4) , they†∗1
∗2
∗3
∗4
∗5
∗6
∗7N = 50N = 82c)

E(2+) [MeV]a)2
1+0.5 MeV
+1.0 MeV+1.5 MeV

experimental data
shell-model this work
shell-model Ref. 3)
30

3438424634384246 50d)

30

34

38

4246 50 30 34
Proton number Z

38424630∆2p [MeV]

450b)

3
2
150

Fig. 1. a) and c): Energies of the ﬁrst excited 2+ states,
E(2+ ), and b) and d): proton gaps, ∆2p , in the even
N =50 and N =82 isotones, respectively. The black lines(solid, dashed, and dotted) in c) and d) show the resultsof SM calculations assuming an increase of the 1p splitting by 0.5, 1.0, and 1.5 MeV, respectively.

disappear for the N =82 isotones below 132 Sn. The
disappearance of the proton sub-shell closures has its
origin in the small energy gap between the 1p1/2 andthe next single-particle orbital (SPO), independent of
the character of the latter. Figs. 1 c) and d) show
the reappearance of the sub-shell gap when increasing
the energy separation between the 1p1/2 orbit and thenext SPO.
Without the existence of pronounced proton subshell closures the N =82 isotones 120 Sr and 122 Zr should
behave as mid-shell nuclei and consequently enhanced
cross-shell excitations are expected to lead to a reduction of the N =82 shell gap in that region. Such areduction would have a signiﬁcant impact on r-process
calculations and it is therefore concluded that preference should be given to mass models which indeed predict a reduction of the N =82 gap, such as the HFB245)
approach.
References
1) J. Dobaczewski et. al., Phys. Rev. Lett. 72, 981 (1994).
2) J. Taprogge et. al., Phys. Rev. Lett. 112, 132501 (2014).
3) A. F. Lisetskiy et. al., Phys. Rev. C 70, 044314 (2004).
4) T. Fastermann et. al. Prog. Part. Nucl. Phys. 69, 85(2013).
5) S. Goriely et. al., Phys. Rev. C 88, 024308 (2013).

Condensed from the article in Phys. Rev. Lett., Vol. 112,132501 (2014)
Instituto de Estructura de la Materia, CSICRIKEN Nishina Center
Departamento de Fı́sica Teórica, Uni. Autónoma de Madrid
GSI Helmholtzzentrum für Schwerionenforschung GmbH
LPSC, UJF, CNRS, INPG, Grenoble
Department of Physics, Tohoku University
Department of Physics, University of Tokyo-1-

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