RIKEN Accel. Prog. Rep. 48 (2015)

Ⅰ. HIGHLIGHTS OF THE YEAR

Isomer decay spectroscopy of 164 Sm and 166 Gd: mid-shell collectivity
around N=100†
Z. Patel,∗1,∗2 P.-A. Söderström,∗1 Zs. Podolyák,∗2 P. H. Regan,∗2,∗3 P. M. Walker∗2 H. Watanabe∗1,∗4E. Ideguchi∗5 G. S. Simpson∗6 H. L. Liu∗7 S. Nishimura,∗1 Q. Wu,∗8 F. R. Xu,∗8 H. Sakurai,∗1The RIBF-86 Collaboration and the EURICA Collaboration
t1/2 = 600(140) ns

The deformation of nuclei around A = 160 may
influence the elemental abundances in the rare earth
element peak. Macroscopic-microscopic calculations
show a deformation maximum close to N = 104 andZ = 66 (170 Dy)1) . However, these calculations seem tobe contradicted by recent experimental data2,3) . We
utilise the existence of K isomers in this deformed region, to reveal the low-lying excited states in A ≈ 160
nuclei that can provide insight into their deformation.
Neutron-rich Z = 62, 64 isotopes were produced byin-flight fission of a 345 A·MeV 238 U beam with anaverage beam intensity of 10 pnA incident on a 9 Be
target at the RIBF. The secondary RI beam containing the nuclei of interest is passed through BigRIPS
and the ZeroDegree spectrometers that separate andidentify the beam species on an ion by ion basis, using
TOF, Bρ and ∆E. The ions of interest were implanted
in a stopper and the γ rays emitted following isomeric
decay were detected using EURICA (Euroball-RIKEN
Cluster Array): 84 HPGe crystals arranged in a 4π
configuration around the stopper.

(37)

1119

137

(5 )
(4 )
(3 )

(5 )
669
(6 )

1009

1280

energy surface calculations4) with total energy minimised in (β2 , β4 , β6 ) deformation space and γ = 0 sug−+gest a 6− state with a 2-neutron ν 52 [512] ⊗ ν 72 [633]configuration is isomeric in both 166 Gd and 164 Sm.
A key feature of our results are the first 2+ and 4+energies. The systematics of E(2+ ) and E(4+ → 2+ )are shown in Fig. 3. The observed 2+ and 4+ energiesof 166 Gd and 164 Sm are the lowest in their isotopic
chains and of the N = 102 isotones, suggesting they
are the most deformed N = 102 nuclei observed in thisregion to date. Our new points in the systematics also
highlight the increase of E(2+ ) and E(4+ → 2+ ) at
N = 100. This behaviour supports the appearance ofa recently predicted deformed shell gap at N = 1005)
that will influence r-process abundance calculations.

(6 )

100
78

1170

1088
1249

1188

120(6 )

(2 )
0249
100

161
70Fig. 1. Level scheme of 166 Gd obtained in this work.

∗1
∗2
∗3
∗4
∗5
∗6
∗7
∗890
80

6092

SmGdDyErYb240

70

The decay from isomeric states in 166 Gd and 164 Sm(N = 102) has been detected for the first time. The
half-lives of the isomeric states have been measured tobe 950(60) ns and 600(140) ns for 166 Gd and 164 Sm respectively. Their level schemes, seen in Figs. 1 and 2,
were deduced from γ-γ coincidence analysis. Potential†260

SmGdDyEr
Yb

110

E(2+) keV

(4 )

156

Fig. 2. Level scheme of 164 Sm obtained in this work.

939
1224

242

(4 )
(2 )
0183
178

911

E(4+ → 2+) keV

t1/2 = 950(60) ns146(5 )(4 ) 105

(6 )

349

220200180160949698N10010210410614092949698

100 102 104 106

NFig. 3. Systematics of E(2+ ) and E(4+ → 2+ ) for Sm, Gd,Dy, Er and Yb isotopes. All data points from ENDSDF
and this work.

References

Condensed from the article in Phys. Rev. Lett. 113, 262502(2014)RIKEN Nishina Center
Department of Physics, University of Surrey
Radioactivity Group, National Physics Laboratory
Department of Physics, Beihang University
RCNP, Osaka University
LPSC, UJF, CHRS, INPG, Grenoble
Department of Applied Physics, Xi’an Jiaotong University
School of Physics, Peking University1) P. Moller et al., Atomic and Nuclear Data Tables 59,185 (1995).
2) E. F. Jones et al., Journal of Physics G 30, L43 (2004).
3) P.-A. Söderström et al., Phys. Rev. C 81, 034310 (2010).
4) F. Xu, et al., Phys. Lett. B 435, 257 (1998).
5) S. K. Ghorui, et al., Phys. Rev. C 85, 064327 (2012).

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