Ⅱ-2. Nuclear Physics (Theory)

RIKEN Accel. Prog. Rep. 50 (2017)

Three-body model for IS spin-triplet neutron-proton pair in 102 Sb†Y. Tanimura∗1 and H. Sagawa∗2,∗3
As the progress of radio-isotope beam facilities allows to access nuclei near the N = Z line, the neutronproton pairing has been attracting more interest thanbefore. In general, a condition expected to maximize
the chance for valence nucleons to form T = 0 pairs isthat they lie in the orbitals on top of a N = Z closedshell core, and that both j> and j< orbitals with low
l are vacant in the valence space. In addition, a large
nuclear mass is favorable because the eﬀect of the spinorbit ﬁeld at the surface becomes relatively weak. In
the present study, we focus on the 102 Sb = 100 Sn+p+nsystem, the core of which, 100 Sn, is the largest N = Z
doubly-magic nucleus located immediately below theproton drip line. In this system, the valence nucleons can occupy d-wave states as in the 18 F nucleus, inwhich the strong eﬀect of the (S, T ) = (1, 0) couplingchannel is observed as an implementation of the good
SU(4) symmetry.1)
In the present study where we have 100 Sn as thecore, we take a self-consistent mean-ﬁeld Hamiltonian
for the single-particle part, H = hHF (p) + hHF (n) +Vres (p, n), where hHF is the single-particle HartreeFock Hamiltonian. For the residual interaction Vres , wetake density-dependent zero-range pairing interactions
which have both spin-singlet and spin-triplet channels.
We calculate the neutron single-particle energies inthe 100 Sn nucleus with three non-relativistic (SLy4,SkM∗ , and SIII) and three relativistic point-coupling(PC-F1, PC-PK1, and PC-LA) EDFs. In particular,
we found that, with the relativistic interactions, the1g7/2 level is nearly degenerate with the 2d5/2 level. In
contrast, with the Skyrme functionals except for SIII,
the 1g7/2 level is located well above the 2d5/2 state andclose to the 2d3/2 level. This diﬀerence may induce
a substantial eﬀect on the structure of the system aswell as the (T = 0, S = 1) pair coupling because it
prevents the valence nucleons from eﬃciently gaining
the pairing energy in (d)2 conﬁgurations. This neardegeneracy with the relativistic EDFs is due to thepseudo-spin symmetry which originates from the cancellation of large scalar and vector ﬁelds. Note thata γ ray of 172 keV between the ﬁrst-excited and theground states of 101 Sn has been measured in Refs.2,3)
and interpreted as a single-neutron transition between
the d5/2 and g7/2 levels.
We have applied a new three-body model based on
self-consistent HF ﬁelds to the 102 Sb = 100 Sn + p + nnucleus. The low-lying 0+ and 1+ states are discussed†∗1∗2∗3Fig. 1. (Color online) Gamow-Teller strength distributions
as a function of the excitation energy from the groundstate of 102 Sn. The ratio between IS and IV pairingstrength is taken as f = 1.5.

in terms of the relation between their excitation energies and the coupling between the two valence nucleonsin the T = 0 channel. The T = 1 interaction strength
is ﬁxed by the empirical neutron pairing gap, and the+T = 0 strength is estimated from the 1+1 and 01 energy
diﬀerences in known N = Z odd-odd nuclei.
We show in Fig. 1 the B(GT) distribution as afunction of the excitation energy with respect to the1020+Sn. A clear diﬀerence between non1 state ofrelativistic and relativistic cases is observed while thelow-lying 0+ and 1+ energy spectra are similar to eachother, i.e., the strength distribution is concentrated
at the ﬁrst peak for SLy4 and SkM*, whereas it isfragmented into the ﬁrst and second peaks for PCF1, PC-PK1, and PC-LA. SIII shows a characteristic
in between those of the two types of EDFs. By analyzing the compositions of wave functions, we observethat the enhanced occupation of the g7/2 orbital in therelativistic model breaks the (L, S, T ) = (0, 1, 0) coupling scheme of the two valence nucleons, and it resultsin the substantial diﬀerence in the low-lying GamowTeller strength distributions.
In conclusion, it is expect that the coupling in the(L, S, T ) = (0, 1, 0) channel is strongly suppressed in
the 100 Sn + p + n nucleus owing to the g7/2 orbital,
which is nearly degenerate with the d5/2 orbital. Theeﬀect appears clearly in the low-lying B(GT− ) distribution rather than in the energy diﬀerence between 1+1and 0+
1 states.
References

Condensed from the article in Phys. Rev. C93, 064319(2017)
Institut de Physique Nucléaire, Université Paris-Sud
RIKEN Nishina Center
Center for Mathematics and Physics, University of Aizu

1) Y. Tanimura, H. Sagawa, K. Hagino, Prog. Theor. Exp.
Phys. 2014, 053D02(2014).
2) D. Seweryniak et al., Phys. Rev. Lett. 99, 022504(2007).
3) I. G. Darby et al., Phys. Rev. Lett. 105, 162502(2010).

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