Ⅱ-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 56 (2023)
RIKEN
Accel. Prog. Rep. 56 (2023)

26

Si + α resonant scattering measurement to study 26 Si(α, p)29 P
reaction rate

M. J. Kim,∗1 K. Y. Chae,∗1 K. Okawa,∗2 S. Hayakawa,∗2 S. Adachi,∗3 S. M. Cha,∗4 T. Chillery,∗2 N. N. Duy,∗1T. Furuno,∗3 G. M. Gu,∗1 S. Hanai,∗2 N. Imai,∗2 D. Kahl,∗5 T. Kawabata,∗3,∗6 C. H. Kim,∗1 D. Kim,∗4S. H. Kim,∗1 S. Kubono,∗6 M. S. Kwag,∗1 J. Li,∗2 N. R. Ma,∗2 S. Michimasa,∗2 K. Sakanashi,∗3 H. Shimizu,∗2O. Sirbu,∗5 N. K. Uyen,∗1 H. Yamaguchi,∗2 R. Yokoyama,∗2 and Q. Zhang∗2An X-ray burst can be characterized by a sudden
and intense release of X-ray radiation from a compact
stellar object such as a neutron star. A total energy
release of approximately 1039–40 ergs can be achieved
per burst in just a few seconds. It is believed thatthe proton-rich nuclei up to the Sn-Sb-Te region canbe synthesized during the burst. To better understandthe X-ray bursts, studying the 26 Si(α, p)29 P reaction
is essential since 26 Si is considered to be one of thewaiting points in the nucleosynthesis.
A sensitivity study, which identiﬁes the importantnuclear reaction rates that aﬀect the X-ray light curves
or ash composition, suggests that the 26 Si(α, p)29 P is
one of the impactful reactions to the light curve of
the X-ray burst.1) Despite its importance, the study of26Si(α, p)29 P is less understood experimentally. Thus
we have performed a 26 Si + α experiment to measure the 26 Si(α, p)29 P reaction directly and the resonant scattering to investigate resonances in 30 S, which
can be populated in the 26 Si(α, p)29 P reaction as intermediate states. The result on the 26 Si + α resonant
scattering is described in this report.
The 26 Si + α resonant scattering was measured
at the Center for Nuclear Study Radioactive Ion
Beam Separator (CRIB)2) of the University of Tokyo.
The radioactive 26 Si beam was produced at E =2.14 MeV/nucleon through the 3 He(24 Mg, n)26 Si reaction by impinging 24 Mg at E = 7.56 MeV/nucleon ona cryogenic 3 He gas target.3) The 26 Si beam was separated and puriﬁed by combining the magnetic analysis
and velocity selection with a double achromatic system
and a Wien ﬁlter. Two PPACs were located at the upstream of the reaction target for the event-by-event
monitoring of beam position and time-of-ﬂight. The
typical 26 Si beam intensity was 2.8 × 104 pps, and thebeam purity was ∼16%. The 26 Si beam was impinged
on the 4 He gas target with a pressure of 250 Torr. Thereaction target was kept at room temperature. The
thick target method is adopted for the experiment toscan a wide excitation energy range in 30 S.
The light charged particles were measured by silicon detector telescopes. Using four layers of silicon∗1∗2∗3∗4∗5∗6detectors (∆E1, ∆E2, E1, and E2 layer), each speciesof charged particles could be easily identiﬁed. The∆E1 and ∆E2 detectors are segmented into 16 strips
providing the horizontal and vertical position information, respectively. The E1 and E2 detectors are
pad type silicon detectors. The scattering angle wasobtained based on the position information. To obtain the excitation function of 26 Si(α, α)26 Si reaction,
the α energies were converted to the center-of-massenergy by considering the kinematics of the reaction
and the energy loss of particles in the gas target. Figure 1 shows the excitation function obtained at θC.M.
= 174◦ . Fitting the experimental excitation function
with the theoretical R-matrix calculations, we will extract resonance parameters of levels in the 30 S, such as
excitation energy, spin, parity, and α partial width, toconstrain the 26 Si(α, p)29 P reaction rate.
250d/dc.m.[mb/sr]

200150100500234567Center of mass energy [MeV]

8Fig. 1. Excitation function of 26 Si + α elastic scattering atθc.m. = 174◦

References
1) R. H. Cyburt et al., Astrophys. J. 55, 830 (2016).
2) Y. Yanagisawa et al., Nucl. Instrum. Methods Phys.
Res. A, 539, 74 (2005).
3) H. Yamaguchi et al., Nucl. Instrum. Methods Phys. Res.
A 589, 150 (2008).

Department of Physics, Sungkyunkwan University
Center for Nuclear Study, University of Tokyo
Department of Physics, Osaka University
Center for Exotic Nuclear Studies, Institute for Basic Science (IBS)
Extreme Light Infrastructure Nuclear Physics (ELI-NP)
RIKEN Nishina Center- 28 -