Ⅱ-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 48 (2015)

Decay spectroscopy of neutron-rich rare-earth isotopes

Dy
Dy

174
174

Dy
Dy

172
172

170
170

66
66
64
64
62
62
2.54
2.54

2.56
2.56

2.58
2.58

2.6
2.6

2.62
2.62

2.64
2.64

2.66 A/q
2.66
A/qFig. 1. Combined particle identification obtained during
the two settings in the experiments.

8 → 8+

60

6+→ 4+

4+→ 2+
2 → 0+

20+30

x-rays40

8+→ 6+-50

100050∗1RIKEN Nishina Center∗2 Department of Physics, University of Surrey∗3 National Physical Laboratory, Teddington∗4 IRCNPC, Beihang University∗5 School of Physics and Nuclear Energy Engineering, BeihangUniversity∗6 Hong Kong University∗7 INR, Hungarian Academy of Sciences∗8 Department of Physics, Chung-Ang University∗9 Department of Physics, Tohoku University∗10 Hanoi University of Science∗11 School of Physics, Peking University∗12 Department of Physics, Osaka University∗13 Department of Physics, Almajmaah University∗14 School of Computing, Engineering and Mathematics, University of Brighton∗15 Department of Physics, Sungkyunkwan University∗16 School of Physics and Astronomy, University of Edinburgh∗17 RCNP, Osaka University∗18 GSI, Darmstadt∗19 Nuclear Engineering Division, Argonne National Laboratory∗20 Department of Nuclear Physics, Australian National University∗21 Hoseo University∗22 IFIN-HH, Bucharest∗23 School of Physics, University College Dublin∗24 Department of Physics, University of Tokyo∗25 INFN-LNL, Legnaro

HoHo6868

Counts

The region in the nuclear chart between 50 < Z < 82
and 82 < N < 126 is the largest region between traditional nuclear shells and, thus, ideal to study theevolution of collectivity and K isomerism originatingfrom the high-j orbitals around mid-shell. Neglecting any potential sub-shell closures, the nucleus withthe largest number of valence particles in this region is170
Dy with proton number Z = 66 and neutron number N = 104. Accordingly it should be one of the mostcollective of all nuclei with A < 208, in its ground state.
From the high degree of axial symmetry and large deformation we expect several long lived, pure K isomers.
In particular, we expect a N = 104, K = 6+ isomer in170
Dy and a N = 106, K = 8− isomer in 172 Dy, similar
to the N = 102, K = 6− isomers in 166 Gd and 164 Sm
recently published1) .
A EURICA experiment was carried out in November
2014, where a 345 MeV/u 238 U beam impinged on aBe target and the fragments separated and identified
in the BigRIPS separator and the ZeroDegree spectrometer and implanted in the WAS3 ABi active stopper. The experiment was carried out with two settings,
13.5 hours centering on 170 Dy and 45 hours centering

ZZ

P.-A. Söderström,∗1 P.H. Regan,∗2,∗3 P. Walker,∗2 H. Watanabe,∗4,∗5 J.J. Liu,∗6 P. Doornenbal,∗1 Z. Korkulu,∗7P. Lee,∗8 G. Lorusso,∗1,∗3 S. Nishimura,∗1 T. Sumikama,∗9 P. Vi,∗10 J. Wu,∗1,∗11 A. Yagi,∗12 G.X. Zhang,∗5T. Alharbi,∗13 H. Baba,∗1 F. Browne,∗14 A.M. Bruce,∗14 R. Carroll,∗2 K.Y. Chae,∗15 Zs. Dombradi,∗7A. Estrade,∗16 N. Fukuda,∗1 C. Griffin,∗16 E. Ideguchi,∗17 N. Inabe,∗1 T. Isobe,∗1 H. Kanaoka,∗12I. Kojouharov,∗18 F.G. Kondev,∗19 T. Kubo,∗1 S. Kubono,∗1 N. Kurz,∗18 I. Kuti,∗7 S. Lalkovski,∗2 G. Lane,∗20E.J. Lee,∗21 G. Lotay,∗2 C.-B. Moon,∗21 I. Nishizuka,∗9 C.R. Nita,∗14,∗22 A. Odahara,∗12 Z. Patel,∗2Zs. Podolyák,∗2 O.J. Roberts,∗23 H. Sakurai,∗1,∗24 H. Schaffner,∗18 C.M. Shand,∗2 H. Suzuki,∗1 H. Takeda,∗1S. Terashima,∗5 Zs. Vajta,∗7 J.J. Valiente-Dòbon,∗25 Z.Y. Xu,∗6 and S. Yoshida∗12100

150200250300350400

450 500Eγ (keV)Fig. 2. Combined γγ-coincidence spectrum gated on thedecays from the 8− isomer in 174 Er.

on 172 Dy. The combined PID is shown in Fig. 1.
In Fig. 2, the decay of the known N = 106, K = 8−
isomer in 174 Er2) is shown. This shows the capabilities
to measure very long lived isomers by triggering onconversion electrons in the 4+ → 2+ and 2+ → 0+transitions, in this case populated by the β-decay of174
Ho. This is not only the heaviest nucleus that has
been measured in EURICA but, with a half life of 4.0 s,
it is also the longest lived isomer. Besides the 170 Dy,
172
Dy, and the previously known 174 Er isomers, theexperimental data set contains several new isomers, βdelayed γ-rays and new β-decay half-lives. All of theseare currently under analysis.
References
1) Z. Patel, et al.: Phys. Rev. Lett. 113, 262502 (2014).
2) G. D. Dracoulis, et al.: Phys. Rev. C 79, 061303 (2009).

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