RIKEN Accel. Prog. Rep. 50 (2017)

Ⅰ. HIGHLIGHTS OF THE YEARFirst direct measurement of the 11 C(α, p)14 N stellar reaction by anextended thick-target method†
S. Hayakawa,∗1 S. Kubono,∗1,∗2,∗3 D. Kahl,∗4 H. Yamaguchi,∗1 D. N. Binh,∗5 T. Hashimoto,∗6Y. Wakabayashi,∗2 J. J. He,∗3 N. Iwasa,∗2,∗7 S. Kato,∗8 T. Komatsubara,∗2 Y. K. Kwon,∗6 and T. Teranishi∗9The 11 C(α, p)14 N reaction is one of the important αinduced reactions competing with β-limited hydrogenburning processes in high-temperature explosive stars.
1,2)
We directly measured its reaction cross sections forthe (α, p0 ), (α, p1 ) and (α, p2 ) transitions to derive thetotal reaction rate at relevant stellar temperatures byan extended thick-target method featuring the time ofﬂight of the recoil proton corresponding to each transition. This report is a condensed version of our article.3)
The measurement was performed in inverse kinematics with 11 C beams at 10.12 MeV and 16.86 MeV produced at CRIB (Center for Nuclear Study RadioactiveIon Beam separator8) ). The experimental setup consisted of two beam-tracking monitors (PPAC: parallelplate avalanche counter and MCP: microchannel plate
detector), a 4 He gas target, and ΔE-E positionsensitive silicon detectors at three diﬀerent angles. We
carefully designed the target length (140 mm) andpressure (400 Torr). Such an extended gas target enables us to diﬀerentiate the transitions to the groundstate and the excited states of 14 N in time of ﬂight(TOF) between the ﬁrst PPAC and the silicon telescopes. The observed TOF vs. recoil proton energy
had several loci with a typical TOF diﬀerence of 5 ns sothat the diﬀerent excited-state transitions were identiﬁed and extracted. The present (α, p1 ) and (α, p2 )cross sections are about one order of magnitude smaller
than the (α, p0 ) one, and those of the Hauser-Feshbach
calculation4) appear to be larger than the present experimental data.
Figure 1 shows the absolute 11 C(α, p)14 N reaction
rates of the present data and the currently available
data4–6) (upper) and their ratios to the CF885) data
(lower). The hatched regions in the lower panel indicate the errors of the present rates. In the νp-processtemperature range (T9 = 1.5–3)2) , the present (α, p0 )reaction rate is enhanced from the CF88 rate by about
40% at most, mainly due to the resonances around
0.9 MeV and 1.35 MeV, which were not taken into account in the previous compilation works.5,6) The con†
∗1
∗2
∗3
∗4
∗5
∗6
∗7
∗8
∗9Fig. 1. Absolute 11 C(α, p)14 N reaction rates of the present
data and the currently available data4–6) (upper) andtheir ratios to the CF885) data (lower). The uncertainties of the present (α, p0 ) rate and total rate are drawn
as hatches attached in the bottom panel.

tribution from the (α, p1 ) and (α, p2 ) reaction rate tothe total reaction rate is about 20% of the (α, p0 ) at
most. The new total reaction rate lies between theprevious (α, p0 ) rate5) and the total Hauser-Feshbachrate,4) which supports the validity of relevant explosive hydrogen-burning process scenarios such as theνp-process that proceeds via the 11 C(α, p)14 N reactionin addition to the triple-α process.
References

Condensed from the article in Phys. Rev. C 93, 065802 (2016)
Center for Nuclear Study, University of Tokyo
RIKEN Nishina Center
Institute of Modern Physics, Chinese Academy of Science
School of Physics and Astronomy, University of Edinburgh
Institute of Physics, Vietnamese Academy for Science andTechnology
Rare Isotope Science Project, Institute for Basic Science
Department of Physics, Tohoku University
Department of Physics, Yamagata University
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