Ⅱ-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 53

Measurement of 25 Al+p resonant elastic scattering relevant to theastrophysical reaction 22 Mg(α, p)25 AlJ. Hu,∗1 H. Yamaguchi,∗2 S. W. Xu,∗1 N. T. Zhang,∗1 S. B. Ma,∗1 L. H. Ru,∗1 E. Q. Liu,∗1 T. Liu,∗1S. Hayakawa,∗2 L. Yang,∗2 H. Shimizu,∗2 D. Kahl,∗3 C. B. Hamill,∗3 A. Murphy,∗3 J. Su,∗4 X. Fang,∗5 K. Chae,∗6M. Kwag,∗6 S. Cha,∗6 N. N. Duy,∗6 N. K. Uyen,∗6 D. Kim,∗6 G. Pizzone,∗7 M. L. Cognata,∗7 S. Cherubini,∗7S. Romano,∗7 A. Tumino,∗7 J. Liang,∗8 A. Psaltis,∗8 M. Sferrazza,∗8 D. H. Kim,∗9 and S. Kubono∗10
Type-I X-ray bursts are the most frequently observed thermonuclear explosions in nature.1) They occur on the surface of accreting neutron stars in lowmass X-ray binary systems. The investigation of Xray bursts can help us understand the properties of aneutron star and the underlying physics.
The bursts are driven by the tripe-α reaction, theαp-process, and the rp-process. After breakout fromthe hot CNO cycle, the nucleosynthesis path is characterized by the αp-process.2) The αp-process is a sequence of α- and proton-induced reactions that transport nuclear material from the CNO cycle toward theregion of heavier proton-rich nuclei.
The X-ray light curve is the main direct observableof X-ray bursts and could be aﬀected signiﬁcantly by
the αp-process. According to a recent sensitivity study
by Cyburt,3) the 22 Mg(α, p)25 Al reaction is thought tobe the most sensitive one during the αp-process andmay have a prominent impact on the burst light curve.
However, with scarce experimental information on thisreaction, the reaction rate in the calculations of X-raybursts is estimated based on statistical models.
A measurement of 25 Al+p resonant elastic scattering has been performed to experimentally examine the22Mg(α, p)25 Al reaction rates. The experiment wasperformed using the CNS radioactive ion beam separator (CRIB),4) installed by the Center for Nuclear Study(CNS), University of Tokyo, in the RIKEN Accelerator
Research Facility. A primary beam of 24 Mg8+ was accelerated up to 8.0 MeV/nucleon by the AVF cyclotron
with an average intensity of 1 eµA. The primary beam
bombarded a liquid-nitrogen-cooled D2 gas target toproduce a secondary 25 Al beam via the 24 Mg(d, n)25 Al
reaction in inverse kinematics. The 25 Al beam wasseparated by the CRIB separator. The 25 Al beam,with an average energy of 5.68 MeV/nucleon and anaverage intensity of 2.0 × 105 pps, was then delivered to the F3 experimental chamber, where it bom-50 cm

26 cm

23 cm

MCP (CH 2) nPPAC25Al23°targetpFig. 1. Schematic diagram (top view) of the experimental
setup at the F3 chamber.

barded a 13.95-mg/cm2 -thick (CH2 )n target and a
18.02-mg/cm2 -thick C target in which the beam wasstopped. The C target was used to evaluate the background contributions. After passing through a Wienﬁlter, the 25 Al beam purity can be up to 80%.
The setup at the F3 experimental chamber is shownin Fig. 1. A parallel-plate avalanche counter (PPAC)
and a micro channel plate (MCP) were used for measuring the time and position information of the beamparticles. The beam particles were identiﬁed in anevent-by-event mode using the abscissa of MCP and
the time of ﬂight between MCP and the RF signal
provided by the cyclotron.
The recoiling light particles from the 25 Al+p reaction were measured using three sets of Si telescopes ataverage angles of θlab ≈ 0◦ , 20◦ , and 23◦ , respectively.
Each telescope consisted of a 65-µm-thick double-sidestrip (16 × 16 strips) silicon detector and two 1500µm-thick pad detectors. The recoiling particles wereclearly identiﬁed using the ∆E-E method. An array often NaI(Tl) detectors was mounted directly above thetarget and used to detect the γ rays from the decayof the excited states in 25 Al. The data analysis is inprogress.
References

1) W. H. G. Lewin, J. V. Paradijs, R. E. Taam, Space
Science Reviews 62, 223 (1993).
2) R. K. Wallace, S. E. Woosley, Astrophys. J. Suppl. 45,389 (1981).
3) R. H. Cyburt et al., Astrophys. J. Suppl. 830, 55 (2016).
4) Y. Yanagisawa et al., Nucl. Instrum. Methods Phys.
Res. A 539, 74 (2005).

∗1Institute of Modern Physics, Chinese Academy of Sciences
Center for Nuclear Study, University of Tokyo∗3 School of Physics & Astronomy, University of Edinburgh∗4 College of Nuclear Science and Technology, Beijing NormalUniversity∗5 School of Physics, Sun Yet-sen University∗6 Department of Physics, Sungkyunkwan University∗7 INFN-LNS, Laboratori Nazionali del Sud∗8 Department of Physics & Astronomy, McMaster University∗9 Department of Physics, Ewha Womans University∗10 RIKEN Nishina Center∗2- 55 -