Ⅱ-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 47 (2014)

Measurement of alpha elastic scattering on 15 O
A. Kim,∗1 K. Y. Chae,∗1 M. S. Gwak,∗1 S. M. Cha,∗1 S. H. Choi,∗2 Y. H. Kim,∗2 H. W. Chae,∗2 K. I. Hahn,∗3
D. H. Kim,∗3 G. W. Kim,∗3 S. Y. Han,∗3 P. S. Lee,∗4 J. Y. Moon,∗5 H. Yamaguchi,∗6 D. Kahl,∗6 and T. Nakao∗6
The measurement of alpha elastic scattering on 15 O
for studying the resonance states of 19 Ne was performed by using the CRIB (CNS Radioactive Ion Beamseparator) at the Center for Nuclear Study, Universityof Tokyo. Alpha-cluster structures have been an interesting subjects of study. Several investigations ofalpha-cluster structures have been conducted on 4N
nuclei such as 8 Be, 12 C, 16 O, and 20 Ne.1–3) In the caseof 19 Ne, because the system of nuclei can be regarded
as 20 Ne plus one hole, weakly coupled states of thealpha and hole have been studied theoretically in the
low-excitation energy region, but limited experimental
data are available, till date. Therefore, experimental
study of alpha elastic scattering on 15 O is very crucial
for understanding how alpha clustering is manifested
in proton-rich nuclei. Unknown alpha-cluster statesof 19 Ne from 1− and 3− members (Kπ = 0− clusterband of 20 Ne) as well as 4+ and 6+ members (Kπ =0+ cluster band of 20 Ne) can be identiﬁed by performing alpha elastic scattering on 15 O. Because the studyof alpha cluster states of 19 Ne has been carried out
theoretically, this experimental result can be used toconﬁrm the alpha-cluster structure of Z>N nuclei ofNe isotopes.4,5)
Moreover, astrophysically, the 18 F(p, α)15 O reaction
is very important because the amount of 18 F produced
in a nova depends sensitively on the reaction ratesof 18 F(p, α)15 O and 18 F(p, γ)19 Ne.6) To date, experimental studies using 18 F beams as well as theoreticalworks have been reported competitively. However, resonance parameters of relevant states above the proton
threshold at Ex = 6.411 MeV have not been conﬁrmed
and remain controversial.7–9) Therefore, if the resonance properties of 19 Ne using 15 O(α, p)18 F are studied, which is a time reverse reaction of 18 F(p, α)15 O, wecan expect better results because the 15 O + α threshold energy is only 3.53 MeV(Ex of 19 Ne).
In this study, the 15 O(α, α)15 O reaction was measured in the energy range Ec.m. = 1.5 − 7.1 MeV,
which corresponds to Ex = 5.0 − 10.6 MeV of 19 Ne.
The primary beam, 15 N (7.0 MeV/u, 0.6 pµA), wastransported from the AVF cyclotron and impinged
on a hydrogen gas target with a thickness of 1.09
mg/cm2 . The secondary beam, 15 O, was obtained bythe p(15 N,n)15 O reaction. Fig. 1 shows beam identiﬁcation for 15 O and other contaminations on the F2
∗1
∗2
∗3
∗4
∗5
∗6Fig. 1. Secondary beam identification on the F2 focalplane.

focal plane. The main contamination of the secondary
beam was 15 N, the primary beam. 15 O beams of 6×105
counts/s were collected at the F3 chamber which contains He gas and a Si telescope and the beams were 96% pure after passing through a Wien ﬁlter. The energy of the 15 O beam was 34 MeV after the entrance
window (Mylar 25 µm-thick) of the F3 chamber.
For inducing alpha elastic scattering, we ﬁlled He gas
directly in the F3 chamber without a special gas cell.
We installed the one-set telescope of consisting two Silayers (20 µm-thick and 480 µm-thick, respectively)
at zero degrees; it was located at a distance of 200
mm from the entrance window of the chamber and thepressure of 4 He gas was 760 Torr at room temperature,
which is equivalent to that for an eﬀective thickness of
3.33 mg/cm2 . The data are currently being analyzed.
References
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2) H. Horiuch et al.: Suppl. Prog. Theor. Phys. 192, 1(2012)3) M. Freer : Rep. Prog. Phys. 70, 2149 (2007)
4) F. Nemoto and H. Bando: Prog. Theor. Phys. 47,1210(1972)
5) T. Sakuda and F. Nemoto: Prog. Theor. Phys. 62, 1274
(1979)
6) M. Hernanz et al.: Astrophys. J. 526, L97 (1999)
7) D. W. Bardayan et al.: Phys. Rev. C 70, 015804 (2004)
8) H. Fortune et al.: Phys. Rev. C 73, 024302 (2006)
9) A. St. J. Murphy et al.: Phys. Rev. C 79, 058801 (2009)

Department of Physics, Sung-Kyun-Kwan University
Department of Physics, Seoul National University
Department of Physics, Ewha Womans University
Department of Physics, Chung-Ang University
RISP, Institute for Basic Science
Center for Nuclear Science, University of Tokyo- 25 -