Ⅱ-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 49 (2016)

Measurement of alpha elastic scattering on 15 O
A. Kim,∗1,∗2 D. H. Kim,∗1 G. W. Kim,∗1 S. Y. Park,∗1 E. K. Lee,∗1 K. I. Hahn,∗1 K. Y. Chae,∗2 S. W. Hong,∗2S. M. Cha,∗2 M. S. Gwak,∗2 E. J. Lee,∗2 J. H. Lee,∗2 J. Y. Moon,∗3 S. H. Choi,∗4 S. H. Bae,∗4 H. Yamaguchi,∗5S. Hayakawa,∗5 Y. Sakaguchi,∗5 K. Abe,∗5 N. Imai,∗5 N. Kitamura,∗5 O. Beliuskina,∗5 Y. Wakabayashi,∗6S. Kubono,∗6 V. Panin,∗6 N. Iwasa,∗7 K. Daid,∗8 and A. A. Chen∗9The γ rays emitted from novae are dominated bye+ -e− annihilation, of which main source is believed tobe the β + decay of 18 F. The amount of 18 F produced
in nova depends signiﬁcantly on the reaction rates of18F(p, α)15 O and 18 F(p, γ)19 Ne and the former one isknown as the most important destructive reaction.1)
This reaction rate is thought to be dominated by two
resonances, 3/2− and 3/2+ , which are located at Ex =6.74 MeV and 7.07 MeV in 19 Ne, respectively. In particular, the interference term between the strong 3/2+state at 7.07 MeV and the other 3/2+ states aroundthe proton threshold (6.41 MeV) is known to aﬀect thereaction rate signiﬁcantly in the astrophysically important energy region.2) However, the 3/2+ states at Ex= 6.42 and 6.45 MeV are still controversial while the3/2− state at 665 keV above the proton threshold wasobserved clearly.2–6) Therefore, to conﬁrm the energies
and J π assignments of these resonances, the study of19
Ne using 15 O + α would be very useful because alpha threshold energy(3.53 MeV) is much lower thanthe proton threshold energy(6.41 MeV).
A measurement of alpha elastic scattering on 15 O
was performed using the thick target method, which
can provide a continuous excitation function in inverse
kinematics because energy loss occurs steadily throughthick gas cell ﬁlled with 4 He. The primary beam, 15 N
(7.0 MeV/u, 0.6 pµA), was transported from the AVF
cyclotron of the RIKEN Accelerator Research Facility
to the low-energy RI beam separator, called CRIB at
the Center for Nuclear Study, University of Tokyo7)
and impinged on a hydrogen gas target with a thicknessof 1.09 mg/cm2 . The primary target was cooled to 90
K by liquid nitrogen in order to prevent the target
window from breaking due to heat.8)
The secondary beam, 15 O, was obtained by the15p( N,n)15 O reaction. The 15 O beam was selectively
puriﬁed by a Wien ﬁlter system so that the beam purity was 99.9% at the focal plane (F3) of CRIB as
shown in Fig. 1.
The ﬁnal intensity of 15 O beam was 6 × 105 counts/s∗1∗2∗3∗4∗5∗6∗7∗8∗9Fig. 1. Secondary beam distribution in F3 after Wien filter.

at the target. The F3 chamber was ﬁlled with the helium gas of 600 Torr, which was maintained at roomtemperature. For detecting the recoiling alpha particles, two sets of the ∆E-E telescope at 0◦ and 15◦
were installed in the F3 chamber, which was locatedat a distance of 200 mm from the entrance window ofthe chamber. The eﬀective target thickness was 2.63
mg/cm2 . The thicknesses of two detectors are 20 µm
and 480 µm, respectively. The energy of the 15 O beam
was well-deﬁned with 36.0±0.5 MeV after the entrance
window (Mylar 20 µm-thick) of the F3 chamber, whichmeans the measured energy was Ex =3.53-11.13 MeV
in 19 Ne. For subtraction of the background, we performed the measurement of 15 O + Ar using Ar gas
target. The data are being currently analyzed.
References
1) M. Hernanz et al., Astrophys. J. 526, L97 (1999).
2) C. E. Beer et al., Phys. Rev. C 83, 042801(R) (2011).
3) D. W. Bardayan et al., Phys. Rev. Lett. 89, 262501(2002).
4) A. St. J. Murphy et al., Phys. Rev. C 79, 058801 (2009).
5) K. Y. Chae et al., Phys. Rev. C 74, 012801(R) (2006).
6) A. M. Laird et al., Phys. Rev. Lett. 110, 032502 (2013).
7) Y. Yanagisawa et al., RIKEN Accel. Prog. Rep. 30, 183(2001).
8) H. Yamaguchi et al., Nucl. Instrum. Methods Phys. Res.
Sect. A 589, 150 (2008).

Department of Physics, Ewha Womans University
Department of Physics, SungKyunKwan University
RISP, Institute of Basic Science
Department of Physics and Astronomy, Seoul National University
Center for Nuclear Study, University of Tokyo
RIKEN Nishina Center
Department of Physics, University of Tohoku
School of Physics and Astronomy, University of Edinburgh
Department of Physics and Astronomy, McMaster University- 65 -