Research Group for Reactions Involving Heavy Nuclei
Group Leader: A. Andreyev
グループ名, Times
New Roman,point, boldH. Koura, I. Nishinaka, K. Hirose, H. Makii, R. Orlandi,
Members:
K. Nishio,
Y.14Utsuno,
GL、メンバー名, Times New Roman, 12points
R. Léguillon, J. Smallcombe, N. Tamura, R. Tatsuzawa

Shell structure of nuclei has substantial effects on theirmasses, decay modes and reactions. One of the research
objectives of the group is to study the evolution of shellstructure in exotic nuclei by measuring their decay properties,
which enables us to establish a universal shell model. Our groupis also pursuing fission studies for neutron and proton-richnuclei in the region from mercury to very-heavy elements
produced by heavy-ion induced reactions. For experiments, we
exploit the JAEA tandem facility and other facilities inside andoutside Japan.
Recently our group has published 2014 edition of the JAEA
chart of nuclides [1], which is widely used in the nuclear
physics and related communities over the world. In addition tothe known data, the chart includes extensive theoreticalpredictions for yet unobserved nuclei.
Single-neuron orbits near the doubly-magic nucleus 78Ni:
Spectroscopy of the N=49 isotope 79Zn
To understand the evolution of shell structure in exotic regionsof the nuclear chart, single-particle properties of doubly-magic
nuclei and their neighbours are essential to create theoreticalmodels of nucleus. In our recent work [2], neutron singleparticle states in the Z=30, N=49 isotope 79Zn have been
populated using the 78Zn(d,p)79Zn transfer reaction at REXISOLDE, CERN. A radioactive 78Zn beam accelerated to 2.9
MeV/u impinged on a 100 µg/cm2 deuterated polyethylene
target. The Miniball Ge array was used to measure γ rays incoincidence with proton ejectiles detected by the T-REX
segmented Si array. The first excited 5/2+ and 1/2+ states,
corresponding to neutrons occupying the lowest orbits above theN=50 shell gap, could be identified. The analysis of angular
distributions in fact provides evidence for a strong νd 5/2 andνs 1/2 single-particle strength in these states, which lie aroundE*~1 MeV. The new data were compared with state-of-the-art
shell-model calculations, which reproduce the measured energyof the 5/2+ state (in blue in Fig. 1) and also the evolution of the
N=50 gap (revealed by 2-neutron separation energies) in N=49
isotones. This agreement supports the picture of a large N=50
gap at 78Ni (~4.7 MeV), and of a robust magicity of 78Ni.

Fig. 1 Experimental (filled symbols) and calculated (empty symbols)
N=50 gap sizes (red) and energy of the first 5/2+ state in 79Zn(blue) and N=49 isotones (black).

Identifying the origin of exotic isomeric states in neutronrich sulfur isotopes
Neutron-rich sulfur isotopes are known to have several
isomeric states whose configulations have not been wellunderstood. The most exotic case among them is strongly
hindered E2 4+ 1 → 2+ 1 decay in 44S, since in most deformed
nuclei E2 transitions between low-lying yrast states (the loweststate for a given angular momentum) are much enhanced
compared to single-particle estimate. It should be noted that 44S
is known to have significant quadrupole collectivity in spite ofbeing an N=28 semimagic nucleus. In the study [3], we perform
a novel analysis of nuclear shell-model wave functions based on
the variation after angular-momentum projection (AM-VAP),
which allows to extract wave functions in the intrinsic frame. As
shown in Fig. 2, the strong E2 hindrance in 44S is reproduced by
the AM-VAP, as well as by the full shell-model calculation. In
particular, the AM-VAP analysis demonstrates that the 4+ 1 statein 44S is dominated by the K=4 wave function. This result israther unexpected because such so-called high-K isomers havebeen so far identified only in some medium-heavy- and heavymass regions (A>100) where K value becomes an approximately
good quantum number due to the development of axiallysymmetric deformation.

Fig. 2 Comparison of experimental energy levels and B(E2) values
in 44S with full shell-model calculations (Full Calc.) and AMVAP approach. The numbers next to the arrows denote the B(E2)values in e2fm4.

References[1] H. Koura et al., Chart of the Nuclides 2014, JAEA (2015).
[2] R. Orlandi et al., Phys. Lett. B. 740, 298 (2015).
[3] Y. Utsuno et al., Phys. Rev. Lett. 114, 032501 (2015).