Ⅱ-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 53

First attempt at in-beam γ-ray spectroscopy of 100 Sn
S. Chen,∗1 J. Lee,∗1 A. Corsi,∗2 K. Wimmer,∗3 P. Doornenbal,∗4 F. Browne,∗4 M. L. Cortés,∗5 T. Koiwai,∗3,∗4
H. Sakurai,∗3,∗4 A. Algora,∗6 D. Brugnara,∗5,∗7 J. Cederkäll,∗8 J. Gerl,∗9 M. Górska,∗9 G. Haefner,∗10K. Kokubun,∗3 P. Koseoglou,∗11,∗9 S. Kubono,∗4 P. Li,∗1 P. Liang,∗1 J. Liu,∗1 Z. Liu,∗12 T. Lokotko,∗1 J. Park,∗8L. G. Sarmiento,∗8 R. Taniuchi,∗4,∗13 W. Xian,∗1 and I. Zanon∗5ZeroDegree PID

BigRIPS PID

5252
105

101

51

Sn 102Sn100

105

Sn51

104
104

103

4950
103

Z

50

Z

The study of the heaviest self-conjugate exotic doubly magic nucleus 100 Sn and the single-particle natureof its neighboring nuclei are of great importance to thefundamental understanding of nuclear structure andthe astrophysical rp-process path. Owing to the low
production rate, no spectroscopic information, except
β-decay, has been measured for 100 Sn so far. As one ofthe ﬁrst observables for nuclear structure, we aim at
the measurement of the ﬁrst 2+ state of 100 Sn, whichindicates the strength of the N = Z = 50 shell closures. A proposal was made to populate the excitedstates from neutron-removal reations of heavier Sn isotopes to perform an in-beam γ-ray spectroscopy measurement.1) In order to properly estimate the beamtime required, the production cross sections for 100 Sn
through secondary fragmentation reactions need to beknown. We performed an experiment with a beamtime of 4 days to measure the production cross sections of 100 Sn produced in neutron-removal reations
from 101, 102 Sn.
A 124 Xe primary beam at 345 MeV/nucleon was provided by SRC with an average intensity of ∼140 pnA.
The beam impinged on a 5-mm-thick 9 Be target to produce radioactive beams containing neutron-deﬁcient
Sn isotopes with the BigRIPS separator. It was tuned
to center on 101 Sn nuclei while accepting 102 Sn simultaneously. Average beam intensities in front of the secondary targets were 2 pps and 27.5 pps for 101, 102 Sn.
A 5-mm-thick CH2 target and a 3-mm-thick C target were used to induce the 1n- and 2n-removal reactions of 101, 102 Sn on C and H. The beam particles and reaction products were identiﬁed with theBigRIPS and ZeroDegree spectrometers, respectively,via the measurements of Bρ, ∆E, and ToF on an
event-by-event basis. The beam energies were measured to be ∼173 MeV/nucleon in BigRIPS and only
∼98 MeV/nucleon in ZeroDegree. The DALI2+ higheﬃciency γ-detection array2) was employed to detect4910210248

48
10104747
1.96 1.98 2 2.02 2.04 2.06 2.08 2.111.96 1.98 2 2.02 2.04 2.06 2.08 2.1

A/Q

1A/Q

Fig. 1. BigRIPS particle identification (left) and ZeroDegree particle identification (right). The isotopes
101, 102
Sn are selected in BigRIPS, while 100 Sn is selected in ZeroDegree.
Table 1. Number of identified events and rates.
5 mm CH2−1n: 101 Sn→ 100 Sn50+ 53 (1.3/h)−2n: 102 Sn→ 100 Sn50+ 42 (1.0/h)

3 mm C40 (1.0/h)
30 (0.8/h)

the γ rays emitted in ﬂight from reaction products inthe vicinity of 100 Sn.
The particle identiﬁcation plots of BigRIPS and ZeroDegree are shown in Fig. 1. Data were accumulated
for 41 h on a CH2 target and 38 h on a C target.
The total numbers and counting rates of fully stripped100
Sn produced by 1n- and 2n-removal reactions are
summarized in Table 1.
The cross sections on the C target were determinedfrom the number of incident projectiles, the number ofreaction products identiﬁed in ZeroDegree, the atom
number in the target, as well as the ZeroDegree transmission and acceptance measured in the same setting.
The cross sections on H were determined using thedata with the CH2 target, subtracting the contribution measured on the C target, after normalization. Tomaximize the statistics, hydrogen-like charge states of100
Sn in the ZeroDegree were considered to be usedin 1n-removal reactions. Preliminary values for crosssections have been obtained. Several new γ transitions
were also observed in this region. Detailed analyses forcross sections and γ spectroscopy are ongoing.

∗1Department of Physics, The University of Hong Kong
IRFU, CEA, Université Paris-Saclay∗3 Department of Physics, University of Tokyo∗4 RIKEN Nishina Center∗5 INFN-LNL∗6 IFIC Valencia∗7 University of Padova∗8 Department of Physics, Lund University∗9 GSI Helmholtzzentrum Darmstadt∗10 Universté Paris-Saclay, CNRS/IN2P3, IJCLab∗11 Institut für Kernphysik, Technische Universität Darmstadt∗12 Institute of Modern Physics, Chinese Academy of Sciences∗13 Department of Physics, University of York
∗2References

1) J. Lee, A. Corsi, K. Wimmer, RIKEN Proposal (2016).
2) S. Takeuchi et al., Nucl. Instrum. Methods Phys. Res.
A 763, 596 (2014).

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