Ⅱ-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 53

New and comprehensive β- and βp-decay spectroscopy results in thevicinity of 100 Sn†
J. Park,∗1 R. Krücken,∗2 D. Lubos,∗3 R. Gernhäuser,∗3 M. Lewitowicz,∗4 S. Nishimura,∗5 and H. Sakurai∗6 forthe EURICA Collaboration
15

†
∗1
∗2
∗3
∗4
∗5
∗6

QEC or Ex (MeV)

The doubly magic nucleus 100 Sn and other nuclei
with similar mass and atomic numbers possess various
nuclear structure and astrophysical properties of importance.1) It is one of the few regions in the nuclear
chart where experimental observables to be comparedto nuclear shell model (SM) and ab-initio theories werescarce, due to the low production cross section. However, a high radioactive isotope beam production rate
at RIBF enabled a decay spectroscopy experiment on
100
Sn and other N ≈ Z ≈ 50 nuclei, which featured
WAS3ABi2) and EURICA3) detectors for heavy ion
implantation, charged particle decay correlation and
γ-ray spectroscopy.
The database on β-decay and βp-decay half-lives(T1/2 ) and branching ratios (bβ , bβp ) of these protonrich nuclei was greatly expanded, with new or more
precise values. Several nuclei and isomers experienced
notable revisions on their T1/2 and bβp . β-decay endpoint measurements yielded ground-state to groundstate energy diﬀerences for 8 proton-rich nuclei, as
well as the excitation energies of 3 isomeric states (seeFig. 1). The results were consistent with AME2016,4)
mass models and SM calculations. Energy spectraof βp decays were produced with new, comparable orhigher statistics in relation to the available literature.
From EURICA data, 25 new γ rays were observed
and assigned to 10 new states in multiple nuclei, withguidance from empirical SM5) in the (p1/2 , g9/2 ) protonand neutron orbitals above the 76 Sr core. One example is the β-decay and βp decay of 98m In, where theﬁrst observation of βp-delayed γ rays from this isomer
could be assigned to excited states in 97 Cd (see Fig. 2).
As for 97 Cd itself, a new isomer with J π = (1/2− )was proposed based on a new β-delayed γ ray with
Eγ = 1245 keV, whose associated β-decay half-life was0.73(7) s.
A systematic evaluation of the assignment of new excited states to tentative spins and parities was carriedout by comparing the energies of the correspondingstates, between their experimental and theoretical values. The energy discrepancies were less than 300 keV
and/or 20% relative to the experimental excitation energy.

10EXP
DZ33
HB
KTUY05

5090

Rh

92

Pd

AME/NUBASE16
FRDM12
HFB27
SLGM
93

Pd

94

Ag 95Ag
Isotope

97m
96m

96

Cd

Cd

Cd

97

Cd98m

In98

In1290511

70763

Fig. 1. Ground-state to ground-state energy diﬀerencesand excitation energies of isomers deduced from β-decay
endpoint energy measurements. The reader is advised
to refer to the original article for references of the different mass models and SM calculations.

50291

40

1000200

400730201417

30602

Counts / 2 keV

60600
800
E (keV)

1000

1200

1400

Fig. 2. γ-ray spectrum with EURICA, correlated to theβp decay of 98m In. Except for the 511-keV annihilation
γ ray, the peaks labeled in black correspond to known
γ rays in 97 Cd. Those labeled in blue were assigned asde-excitation transitions from new excited states in thesame nucleus.

References
1) T. Faestermann, M. Górska, H. Grawe, Prog. Part.
Nucl. Phys. 69, 85 (2013).
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) M. Wang et al., Chin. Phys. C 41, 030003 (2017).
5) F. J. D. Serduke, R. D. Lawson, D. H. Gloeckner, Nucl.
Phys. A 256, 45 (1976).

Condensed from the article in Phys. Rev. C 99, 034313(2019)
Department of Physics, Lund University
TRIUMF
Physik Department, Technische Universität München
Grand Accélérateur National d’Ions Lourds (GANIL)RIKEN Nishina Center
Department of Physics, University of Tokyo- 31 -