II-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Spectroscopy of 99 Cd and 101 In from β decays of 99 In and 101 Sn†
J. Park,∗1 R. Krücken,∗2 D. Lubos,∗3 R. Gernhäuser,∗3 M. Lewitowicz,∗4 S. Nishimura,∗5 and H. Sakurai∗6 , for
the EURICA Collaboration

†
∗1
∗2
∗3
∗4
∗5
∗6(9/2+) T1/2 = 3.11(6) s(Park 2019)
β+/EC

0Experimental knowledge in the doubly magic 100 Sn
region, relevant for tests of nuclear shell models (SM),proton-neutron interactions in N ≈ Z ≈ 50 nuclei
and the end of the rapid proton-capture process (rpprocess) in nuclear astrophysics, has been expanded
through a β-decay spectroscopy campaign at RIBF.1)
The literature on β decays of 99 In and 101 Sn has been
either nonexistent or contentious due to low statistics,
but subsequent analyses of the β-delayed γ-ray spectroscopy data from the RIBF9 experiment revealed
new states in 99 Cd and addressed the ambiguity concerning the level scheme of 101 In.
Using WAS3ABi2) and EURICA3) detectors whichwere deployed at the end of the ZeroDegree spectrometer, decay events following 99 In and 101 Sn ion implantations were correlated. 30 new γ rays belonging to99
Cd were observed, and a subset of γ rays previously
assigned to 101 In has been conﬁrmed in this measurement. Two new high-energy γ rays were assigned to101
In in this work. The available γ-γ coincidence data
was analyzed to build on the level scheme of 99 Cd,
as shown in Fig. 1. Alternatively, the experimental
energies and intensities of the γ rays were comparedwith the SM calculations based on the SR88MHJM4)
interaction, in a model space of π(2p1/2 , 1g9/2 ) andν(1g7/2 , 2d5/2 , 2d3/2 , 3s1/2 , 1h11/2 ) orbitals above the88
Sr core. The eﬀect of varying eﬀective charges andtheoretical transition energies on the branching ratiosof γ rays was assessed. Tentative assignments of new
excited states were made for both 99 Cd and 101 In,
where a good agreement was found within theoreticaluncertainties. No signiﬁcant inconsistencies in the intensities of γ rays were found between the experimentand theory in a γ-ray energy range of 0–2500 keV.
β-delayed proton emission events from the decay of101
Sn were recorded and incorporated in the γ-ray intensity analysis. The competition between branchingratios of protons versus γ rays from high-energy statesin 101 In was evaluated using a semi-empirical theory
on proton emission.5) The two competing hypotheses
concerning the ground-state spin of 101 Sn, being either
the 5/2+ based on the 2d5/2 single-neutron conﬁguration or the 7/2+ based on the 1g7/2 conﬁguration,
were examined by comparing the experimental γ-ray99In(9/2+)

2227
2057 (17/2+)
1975
226
1831 (13/2+)1781
1675
1607

(9/2+)

1234

2487

1077
883

(1/2+)

883
1077

441

9/2+

2664

9/2+

2376

9/2+

17/2+ 1930
1915
13/2+ 1835

9/2+
5/2+
11/2+

1543
1537

5/2++
7/2

1242

1104

3/2+

886

1/2+

557

7/2+

9/2+

(7/2+)

441

1224

783

(9/2+) 2037
(5/2+) 1769
(11/2+)(7/2+)(3/2+)

1607(9/2+)

1340
1534
1786
1987

607

2428

1224

2956

(9/2+)

2928(5/2+)

099

Cd EXP5/2+099

Cd SMFig. 1. Experimental level scheme of 99 Cd, compared to SM
calculations. Only the states revealed by the β decayof 99 In are shown. The blue arrows indicate new γ rays
observed in this work.

intensities and the integrated β-delayed proton emission branching ratio to theoretical values. Due to theimprecise knowledge of the proton separation energyof 101 In and low experimental γ-ray statistics, there
was insuﬃcient circumstantial evidence for an unambiguous spin assignment of the ground state of 101 Sn.
Determining the single-particle energies of the N = 51
isotones, 99 Cd and 101 Sn, would result in an enhanced
systematic review of the N = 50 shell evolution in theproton-rich nuclei close to 100 Sn.
References

1) J. Park et al., Phys. Rev. C 99, 034313 (2019).
2) S. Nishimura, Prog. Theor. Exp. Phys. 2012, 03C006(2012).
3) P. -A. Söderström et al., Nucl. Instrum. Methods Phys.
Res. B 317, 649 (2013).
4) D. T. Yordanov et al., Phys. Rev. C 98, 011303(R)(2018).
5) D. S. Delion, R. J. Liotta, R. Wyss, Phys. Rep. 424,113 (2006).

Condensed from the article in Phys. Rev. C. 102, 014304(2020)
Center for Exotic Nuclear Studies, Institute for Basic Science
TRIUMF
Physik Department, Technische Universität München
Grand Accélérateur National d’Ions Lourds (GANIL)RIKEN Nishina Center
Department of Physics, University of Tokyo- 23 -1