Physics Letters B 785 (2018) 615–620
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Physics Letters B
www.elsevier.com/locate/physletb
Neutron-hole states in
131
Sn and spin-orbit splitting in neutron-rich
nuclei
R. Orlandi
a,b,c,d,∗
, S.D. Pain
e
, S. Ahn
f
, A. Jungclaus
b
, K.T. Schmitt
f
, D.W. Bardayan
e
,
W.N. Catford
g
, R. Chapman
c,d
, K.A. Chipps
h,e
, J.A. Cizewski
i
, C.G. Gross
e
, M.E. Howard
i
,
K.L. Jones
f
, R.L. Kozub
j
, B. Manning
i
, M. Matos
k
, K. Nishio
a
, P.D. O’ Malley
i
, W.A. Peters
l
,
S.T. Pittman
e
, A. Ratkiewicz
i
, C. Shand
g,i
, J.F. Smith
c,d
, M.S. Smith
e
, T. Fukui
m,n
,
J.A. Tostevin
g,o
, Y. Utsuno
a
a
Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki, 319-1195, Japan
b
Instituto de Estructura de la Materia (IEM), CSIC, Madrid, E-28006, Spain
c
School of Engineering and Computing, University of the West of Scotland, Paisley, PA1 2BE, UK
d
The Scottish Universities Physics Alliance (SUPA), UK
e
Physics Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
f
Department of Physics and Astronomy, University of Tennessee, Knoxville, TN 37996, USA
g
Department of Physics, University of Surrey, Guildford, GU2 7XH, UK
h
Physics Department, Colorado School of Mines, Golden, CO 80401, USA
i
Department of Physics and Astronomy, Rutgers University, New Brunswick, NJ 08903, USA
j
Department of Physics, Tennessee Technological University, Cookeville, TN 38505, USA
k
Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803, USA
l
Oak Ridge Associated Universities, Oak Ridge, TN 37831, USA
m
Nuclear Data Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan
n
Istituto Nazionale di Fisica Nucleare, Complesso Universitario di Monte S. Angelo, Via Cintia, I-80126 Napoli, Italy
o
Department of Physics, Tokyo Institute of Technology, Meguro, Tokyo, 152-8551, Japan
a r t i c l e i n f o a b s t r a c t
Article history:
Received
23 May 2018
Received
in revised form 13 July 2018
Accepted
3 August 2018
Available
online 7 August 2018
Editor: D.F.
Geesaman
Keywords:
Nuclear
structure
Spin-orbit
interaction
Transfer
reactions
Doubly-magic
nuclei
Shell
model
In atomic nuclei, the spin-orbit interaction originates from the coupling of the orbital motion of a
nucleon with its intrinsic spin. Recent experimental and theoretical works have suggested a weakening
of the spin-orbit interaction in neutron-rich nuclei far from stability. To study this phenomenon, we
have investigated the spin-orbit energy splittings of single-hole and single-particle valence neutron
orbits of
132
Sn. The spectroscopic strength of single-hole states in
131
Sn was determined from the
measured differential cross sections of the tritons from the neutron-removing
132
Sn(d, t)
131
Sn reaction,
which was studied in inverse kinematics at the Holifield Radioactive Ion Beam Facility at Oak Ridge
National Laboratory. The spectroscopic factors of the lowest 3/2
+
, 1/2
+
and 5/2
+
states were found
to be consistent with their maximal values of (2 j + 1), confirming the robust N = 82 shell closure at
132
Sn. We compared the spin-orbit splitting of neutron single-hole states in
131
Sn to those of single-
particle
states in
133
Sn determined in a recent measurement of the
132
Sn(d, p)
133
Sn reaction. We found a
significant reduction of the energy splitting of the weakly bound 3p orbits compared to the well-bound
2d orbits, and that all the observed energy splittings can be reproduced remarkably well by calculations
using a one-body spin-orbit interaction and a Woods–Saxon potential of standard radius and diffuseness.
The observed reduction of spin-orbit splitting can be explained by the extended radial wavefunctions of
the weakly bound orbits, without invoking a weakening of the spin-orbit strength.
© 2018 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license
(http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP
3
.
The spin-orbit (SO) interaction, which arises from the coupling
of the orbital motion of a particle with its intrinsic spin, affects the
*
Corresponding author at: Advanced Science Research Center, Japan Atomic En-
ergy
Agency, Tokai, Ibaraki, 319-1195, Japan.
E-mail
address: orlandi.riccardo@jaea.go.jp (R. Orlandi).
properties of a diverse number of systems, such as atomic elec-
trons [1],
carbon nanotubes [2]or quantum gases [3]. In nuclear
physics, the SO interaction is often described in the mean-field
approximation, as a one-body potential term proportional to the
derivative of the nuclear density [4]. In this model, the SO poten-
https://doi.org/10.1016/j.physletb.2018.08.005
0370-2693/
© 2018 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by
SCOAP
3
.