Ⅱ-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 50 (2017)

New measurement of the 34 Si(p, p) reaction
N. Kitamura,∗1 N. Imai,∗1 S. Shimoura,∗1 K. Wimmer,∗2∗3 S. Michimasa,∗1 S. Ota,∗1 O. Beliuskina,∗1P. Schrock,∗1 M. Kobayashi,∗1 Y. Kiyokawa,∗1 Y. Yamaguchi,∗1 S. Masuoka,∗1 H. Ueno,∗3 K. Yoneda,∗3Y. Ichikawa,∗3 T. Teranishi,∗4 N. Shimizu,∗1 and Y. Utsuno∗5
The evolution of shell structure as a function ofthe proton and neutron number has been observed
throughout the nuclear chart. Although this evolution
is visualized as shifts in the single-particle energies, themechanism that changes the single-particle structuresin the vicinity of the so-called island of inversion has
not yet been fully revealed.
The most straightforward way to explore the singleparticle structure is (d, p) one-neutron transfer reactions. In inverse kinematics, (d, p) experiments suffer from low statistics and/or poor resolution because
there are two conﬂicting requirements; on the one
hand, the thickness of the target needs to be limited
to minimize the energy straggling, and on the otherhand, thick targets increase the luminosity. The equivalent spectroscopic information is obtained by meansof isobaric analog resonances (IARs) through proton
resonant elastic scattering because IARs have the same
conﬁguration as the parent states except for the isospin
part. This method is powerful, especially for investigations using RI beams in combination with the thicktarget inverse kinematics, and its eﬀectiveness has been
proven1,2) .
This method has already been applied to the 35 Si nucleus located just outside the island of inversion. Six
IARs were observed by measuring the proton elastic
scattering on 34 Si3) and spectroscopic information was
deduced for each resonance by R-matrix analysis4) .
More recently, a measurement of the 34 Si(d, p) reaction was reported by Burgunder et al.5) , and the resulting spectroscopic factors are in disagreement with
the IAR results. This motivated us to perform a newmeasurement with a modiﬁed experimental setup.
The experiment was performed at the RIKEN Projectile fragment Separator (RIPS) facility. To gain
more statistics than in the previous measurement, theprimary beam species was changed from 40 Ar to 48 Ca.
The primary beam at an energy of 63 MeV/nucleon impinged on a 1.25-mm beryllium production target. Asecondary 34 Si beam was produced with a typical purity of 30 % and an intensity of 40 kpps. Note that theepax 2.15 parameterization6) overpredicted the intensity by an order of magnitude. The beam particles wereidentiﬁed event-by-event by the TOF-ΔE method.
The beam was slowed down to 6 MeV/nucleon using
∗1
∗2
∗3
∗4
∗5Fig. 1. Measured cross sections for 34 Si(p, p) (circles). The
background contribution is assumed to be constant.
The solid line is the R-matrix calculation from the original measurement3) . A calculation assuming the 1/2+state in 35 Si at 1.7 MeV is also shown (dotted).

a carbon rotatable degrader and irradiated a proton
target. The protons were detected downstream of thetarget in a stack of silicon detectors, 0.1, 1.0, 1.5, and
1.5 mm thick. In order to increase the excitation energy window, the conﬁguration was optimized with respect to the original experiment.
The experimental excitation function is shown inFig. 1, together with the R-matrix calculation. Although the statistics were very limited, the R-matrix
curve reproduced our present result except for the strucuture around 4.5 MeV. In our previous measurement,
a detector dead-layer could be present around this region, which potentially caused the distortion of theresonances. A peak at 4.7 MeV has been observed forthe ﬁrst time in this experiment, and this could correspond to the IAR of a 1/2+ state in 35 Si at 1.7 MeV,
considering its shape. The energy is in good agreement with the 1688-keV 1/2+ state that was recentlyobserved by an experiment of the one-neutron knockout from 36 Si7) .
References
1) G. V. Rogachev et al., Phys. Rev. C 67, 041603(R)(2003).
2) N. Imai et al., Phys. Rev. C 90, 011302 (2014).
3) N. Imai et al., Phys. Rev. C 85, 034313 (2012).
4) W. J. Thompson et al., Phys. Rev. 173, 975 (1968).
5) G. Burgunder et al., Phys. Rev. Lett. 112, 042502(2014).
6) K. Sümmerer and B. Blank, Phys. Rev. C 61, 034607(2000).
7) S. R. Stroberg et al., Phys. Rev. C 90 034301 (2014).

Center for Nuclear Study, University of Tokyo
Department of Physics, Univeristy of Tokyo
RIKEN Nishina Center
Department of Physics, Kyushu University
Advanced Science Research Center, Japan Atomic Energy
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