Ⅱ-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 51 (2018)

Isomer-decay spectroscopy of 67 Fe and reaction-channel dependency
of isomeric ratios from interactions in the MINOS proton target
P.-A. Söderström,∗1,∗2,∗3 L. X. Chung,∗4 A. Gillibert,∗5,∗3 B. D. Linh,∗4 A. Obertelli,∗1,∗3,∗5 P. Doornenbal,∗3S. Nishimura,∗3 F. Browne,∗6,∗3 Z. Patel,∗7 C. Shand,∗7 J. Wu,∗3,∗8 G. Authelet,∗5 H. Baba,∗3 D. Calvet,∗5F. Château,∗5 A. Corsi,∗5,∗3 A. Delbart,∗5,∗3 Zs. Dombradi,∗9,∗3 S. Franchoo,∗10 J.-M. Gheller,∗5,∗3F. Giacoppo,∗11 A. Gottardo,∗10 K. Hadyńska-Klȩk,∗11 T. Isobe,∗3 I. Kojouharov,∗2 Z. Korkulu,∗9S. Koyama,∗3,∗12 Y. Kubota,∗3,∗13 N. Kurz,∗2 V. Lapoux,∗5,∗3 J. Lee,∗14 M. Lettmann,∗1 C. Louchart,∗1R. Lozeva,∗15 K. Matsui,∗3,∗12 M. Matsushita,∗13 T. Miyazaki,∗3,∗12 S. Momiyama,∗3,∗12 T. Motobayashi,∗3M. Niikura,∗12,∗3 L. Olivier,∗10 S. Ota,∗13 H. Otsu,∗3 C. Péron,∗5 A. Peyaud,∗5 N. Pietralla,∗1E. C. Pollacco,∗5,∗3 J.-Y. Roussé,∗5,∗3 E. Sahin,∗11 H. Sakurai,∗3,∗12 C. Santamaria,∗3,∗5 M. Sasano,∗3H. Schaﬀner,∗2 Y. Shiga,∗3,∗16 I. G. Stefan,∗10 D. Steppenbeck,∗13,∗3 T. Sumikama,∗17,∗3 D. Suzuki,∗10S. Takeuchi,∗3 R. Taniuchi,∗3,∗12 T. Uesaka,∗3 Zs. Vajta,∗9 H. Wang,∗3 V. Werner,∗1 K. Yoneda,∗3and Z. Y. Xu∗14
In this report, we discuss the properties of the isomeric state in 67 Fe. While the existence of this isomeris already well established, its nature is still unknown.
The data were obtained using the EURICA1,2) setup
during the SEASTAR campaign in 20143) by ﬁssioning
a 345 MeV/u 238 U beam on a 3 mm-thick beryllium
target. Knockout reactions occured in the liquid hydrogen target of MINOS,4) installed at the F8 focal
plane. At the ﬁnal focal plane the EURICA array wasused for measuring the energy and time between implantation and detection of the γ rays. In this experiment only six EURICA clusters were active. A total of∼ 3×107 67 Fe nuclei were implanted in a stopper in thecenter of EURICA. Approximately 96% of these implantation were from unreacted 67 Fe secondary beam,
the rest were reaction products in MINOS.
Using the BigRIPS and ZeroDegree information theimplanted nuclei could be separated into the main
reaction channels: 68 Co(p, 2p)67 Fe, 238 U ﬁssion, and68
Fe(p, pn)67 Fe with isomeric ratios of 56%, 36%, and28%, respectively. Thus, the isomeric ratio is highest
in the proton knock-out channel, but also signiﬁcantin the other channels. In the Fig. 1, the γ-ray spectra
are shown, normalized to the number of incoming ions.
One possible interpretation of the diﬀerent isomericratios is found in the diﬀerence in the states of theγFig. 1. Spectra of γ rays following isomeric decay separated
into the main reaction channels normalised to the respective number of incoming ions.

ternary beam. For 68 Co there are two long-lived statesthat can serve as eﬀective ground state conﬁgurationsof 1− and 7− based on πf7/2 ⊗ νg9/2 . Knocking out af7/2 proton could then leave a g9/2 neutron in an excited state, that in turn decays to the isomeric state.
With 68 Fe in a 0+ ground state, and no other knownlong lived conﬁgurations, the still relatively high isomeric ratio from neutron knockout can be explained
2by the breaking of a νg9/2
neutron-pair. In summary,such a picture would be consistent with a νg9/2 -based
isomer over a νp1/2 ground-state.

∗1

Institut für Kernphysik, Technische Universität Darmstadt
GSI, Darmstadt∗3 RIKEN Nishina Center∗4 INST, Hanoi∗5 CEA, Saclay∗6 School of Computing, Engineering and Mathematics, University of Brighton∗7 Department of Physics, University of Surrey∗8 School of Physics, Peking University∗9 MTA Atomki, Debrecen∗10 IPN Orsay, Orsay∗11 Department of Physics, University of Oslo
∗12 Department of Physics, University of Tokyo∗13 CNS, University of Tokyo∗14 Department of Physics, The University of Hong Kong
∗15 ICSNSM, IN2P3/CNRS, Université Paris-Saclay∗16 Department of Physics, Rikkyo University∗17 Department of Physics, Tohoku University∗2References
1) S. Nishimura, Prog. Theor. Exp. Phys. 2012, 03C006(2012).
2) P.-A. Söderström et al., Nucl. Instrum. Methods B 317,649 (2013).
3) P. Doornenbal et al., RIKEN Accel. Prog. Rep. 48 5(2015).
4) A. Obertelli et al., Eur. Phys. J. A 50, 8 (2014).

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