Ⅱ-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 53

Intermediate-energy Coulomb excitation of 102 Sn

Being presumably the heaviest, particle-bound, doubly magic N = Z nucleus, 100 Sn oﬀers a fundamental
testing ground for nuclear theories. Experimental signatures of shell structure can be provided by the 2+
1energies as well as by the reduced transition probabil+ities, B(E2; 0+gs → 21 ). In the Sn isotopes between
the N = 50 and N = 82 shell closures, the 2+
1 energies are well established and show an almost constant value,1) as expected in the generalized seniority
scheme. Within the same framework, the B(E2)↑ values should resemble an inverted parabola peaking at
mid-shell. However, measurements in the most protonrich Sn isotopes,2–4) have shown a clear deviation fromthe expected behavior.
Diﬀerent calculations based on the large-scale shellmodel as well as on the relativistic quasi-particle
random-phase approximation have been performed inorder to give an account of the measured B(E2)↑ values.5) Although the calculations tend to agree on theneutron-rich side of the chain, signiﬁcant diﬀerences
are observed on the proton-rich side. This is particularly true for 102 Sn, where the diﬀerence between thepredictions amounts to almost a factor of 3, making
this isotope a good candidate for the investigation of
the eﬀects driving the nuclear structure in the vicinity of 100 Sn. In order to elucidate the nuclear structure underlying the measured B(E2)↑ values, the ﬁrst
Coulomb excitation measurement of 102 Sn was performed at the RIBF.6)
A 345 MeV/nucleon beam of 124 Xe with an average intensity of 120 pnA was fragmented on a 5 mm
thick Be target at the entrance of the BigRIPS separator7) to produce 102 Sn. Within the same experimental setting, 100 Cd was also transmitted. The isotopesof interest were identiﬁed on an event-by-event basis using the Bρ-∆E-Bρ technique. Figure 1a) shows
the particle identiﬁcation obtained in BigRIPS, where102
Sn and 100 Cd are clearly visible. A 0.5 mm Au
target placed at F8 was used to induce Coulomb ex-Atomic number

M. L. Cortés,∗1,∗2 F. Browne,∗2 P. Doornenbal,∗2 S. Chen,∗3 A. Corsi,∗4 T. Koiwai,∗5,∗2 J. Lee,∗3H. Sakurai,∗2,∗5 K. Wimmer,∗5 A. Algora,∗6 D. Brugnara,∗1 J. Cederkäll,∗7 J. Gerl,∗8 M. Gorska,∗8G. Haefner,∗9 K. Kokubun,∗5 P. Koseoglou,∗10 S. Kubono,∗2 P. Li,∗3 P. Liang,∗3 J. Liu,∗3 Z. Liu,∗11T. Lokotko,∗3 J. Park,∗7 L. G. Sarmiento,∗7 R. Taniuchi,∗12 W. Xian,∗3 and I. Zanon∗15150102

49 102Sn

Sn48
47

100
100

Cd
Cd100
100
Cd

Cd46a)

45b)

2.04 2.06 2.08 2.10 2.12 2.14
Mass-to-Charge ratio

2.04 2.06 2.08 2.10 2.12 2.14
Mass-to-Charge ratio

Fig. 1. Particle identification in a) BigRIPS, and b) Zerodegree. In both cases 102 Sn and 100 Cd are clearly identified.

citation. In addition, measurements with a 3 mm C
target were performed to obtain the nuclear contribution to the cross section. Outgoing fragments wereidentiﬁed using the ZeroDegree spectrometer, as shownin Fig. 1b). The target was surrounded by the higheﬃciency DALI2+ γ-detector array, composed of 226
NaI(Tl) detectors.8,9) The average beam intensities before the secondary target were 90 pps and 4200 pps for102
Sn and 100 Cd, respectively, with an energy around
177 MeV/nucleon.
As part of the experiment, the incoming beam wasimplanted into a plastic target at F7 for 1 h, and dataon the γ rays emitted following the decay of the isomerwere collected using a HPGe detector. By combining
the information on the number of ions implanted andthe total γ rays observed, the isomeric ratio of thebeam can be obtained. This quantity is fundamental
for the correct determination of the cross section fromthe Coulomb excitation measurement. Finalization ofthe outgoing particle identiﬁcation and further analysis
on the in-beam γ-ray spectra of 102 Sn and 100 Cd isongoing.
References∗1

INFN-Laboratori Nazionali di Legnaro
RIKEN Nishina Center∗3 Department of Physics, The University of Hong Kong
∗4 IRFU, CEA, Université Paris-Saclay∗5 Department of Physics, The University of Tokyo∗6 IFIC Valencia∗7 Department of Physics, Lund University∗8 GSI Helmholtzzentrum für Schwerionenforschung∗9 Université Paris-Saclay, CNRS/IN2P3, IJCLab∗10 Institut für Kernphysik, Technische Universität Darmstadt∗11 Institute of Modern Physics, Chinese Academy of Sciences∗12 Department of physics, University of York1) http://www.nndc.bnl.gov/ensdf/ .
2) G. Guastalla et al., Phys. Rev. Lett. 110, 172501 (2013).
3) V. M. Bader et al., Phys. Rev. C 88, 051301(R) (2013).
4) P. Doornenbal et al., Phys. Rev. C 90, 061302(R) (2014).
5) T. Togashi et al., Phys. Rev. Lett. 121, 062501 (2018).
6) M. L. Cortés, Experiment NP1612-RIBF153R1.
7) T. Kubo, et al., Prog. Theor. Exp. Phys. 2012 (2012).
8) S. Takeuchi et al., Nucl. Instrum. Methods Phys. Res.
A 763, 596 (2014).
9) I. Murray et al., RIKEN Accel. Prog. Rep. 51, 158 (2017).

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