Ⅰ. HIGHLIGHTS OF THE YEARRIKEN Accel. Prog. Rep. 50 (2017)

A directly measurable parameter quantifying the halo nature of
one-neutron halo nuclei†
S. Watanabe,∗1 M. Yahiro,∗2 M. Toyokawa,∗2 and T. Matsumoto∗2

σabs (a) − σabs (c),H=σabs (n)and at about 0.21 for a d-wave non-halo nucleus 17 C.
As a result, the ﬁve lines are well separated into threegroups of s-wave halo, p-wave halo and d-wave nonhalo in the vicinity of Sn = 0. If s-wave halo nuclei
with very small separation energy (Sn  0.01 MeV) are
newly discovered, they should be on or near the line.
This may be also true for p-wave halo nuclei. Therefore, if σR (n), σR (c) and σR (a) are newly measured at
the same incident energy per nucleon, one can derive
H and see the halo nature of the nuclei without model
calculation. H is thus a good indicator quantifying thehalo nature of one-neutron halo nuclei.

 

After the discovery of a halo nucleus 11 Li1) , total reaction cross sections (σR ) and/or interaction cross sections (σI ) were further measured to identify new halonuclei2) . For example, it was established that 11 Be and15,19
C are one-neutron halo nuclei, and 6 He, 11 Li, 14 Be,
and 22 C are two-neutron halo nuclei with Borromeanstructures. Nowadays, the measurements reach the pf shell region, i.e., the vicinity of the neutron-drip linefor Ne and Mg isotopes3,4) ; 31 Ne and 37 Mg are considered to be one-neutron halo nuclei6,7) . Thus, the sudden enhancement of measured σR is a good experimental probe of halo nuclei. However, the relation between
σR and the separation energies of the halo nuclei are
not well understood particularly in the weak-binding
limit.
In this report, we focus on the scattering of oneneutron halo nuclei (a) on a target (T) at high incident
energies (Ein  240 MeV/nucleon) where projectilebreakup eﬀects are expected to be small. At the highincident energies, we can identify σR and σI as absorption cross sections σabs . We also assume that oneneutron halo nuclei (a) are well described by the core+ neutron (c + n) two-body model, and the scatteringof a on T is well explained by the c + n + T three-bodymodel. We now propose the parameter∗1∗2 



(1)
Fig. 1. Behavior of H as a function of Sn . The horizontal
axis is in the logarithmic scale. The theoretical results
are shown by the solid (dotted) line for 11 Be (19 C), thedashed (dot-dashed) line for 31 Ne (37 Mg), the dot-dotdashed line for 17 C, and the dot-dashed line for 15 C.
See Ref.5) for the experimental data.

where σabs (x) is the absorption cross section of x on thesame T at the same incident energy per nucleon. Theparameter H represents an enhancement of σabs (a)from σabs (c) relative to σabs (n), and varies in a range of0 ≤ H ≤ 1. The halo structure is most developed when
H = 1 and least developed when H = 05) . Therefore,
H is expected to quantify the degree of halo nature
regardless of scattering conditions such as Ein or T.
Figure 1 shows the behavior of H as a function of theone-neutron separation energy Sn . Experimental data
is listed in Ref.5) . The results of the present model5) ,which is based on the spherical Woods-Saxon potential
and the Glauber model, are consistent with the empirical values for all halo nuclei 11 Be, 19 C, 31 Ne and 37 Mg
within 1σ error bars. H is then extrapolated to the
Sn = 0 limit as shown by the lines. Only for s-wave
halo nuclei 11 Be and 19 C, the lines reach H = 1 in theSn = 0 limit. On the other hand, the lines saturate
at about 0.55 for p-wave halo nuclei 31 Ne and 37 Mg,†

References
1) I. Tanihata et al., Phys. Rev. Lett. 55, 2676 (1985);
Phys. Lett. B 206, 592 (1988).
2) A. Ozawa et al., Nucl. Phys. A 691, 599 (2001).
3) M. Takechi et al., Phys. Lett. B 707, 357 (2012).
4) M. Takechi et al., Phys. Rev. C 90, 061305(R) (2014).
5) M. Yahiro et al., Phys. Rev. C 93, 064609 (2016).
6) K. Minomo et al., Phys. Rev. Lett. 108, 052503 (2012).
7) S. Watanabe et al., Phys. Rev. C 89, 044610 (2014).

Condensed from the article in Phys. Rev. C 93, 064609(2016)RIKEN Nishina Center
Department of Physics, Kyushu University- 13 -