Ⅱ-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 52 (2019)

New measurement of 8 Li(α, n)11 B reactions
Y. Mizoi,∗1,∗2,∗3 H. Baba,∗3 A. Bracco,∗4,∗5 F. Camera,∗4,∗5 S. M. Cha,∗6 K. Y. Chae,∗6 S. Cherubini,∗3,∗7,∗8
H. S. Choi,∗9 N. N. Duy,∗6 T. Fukuda,∗3,∗10 S. Hayakawa,∗2 Y. Hirayama,∗11 N. Imai,∗2 H. Ishiyama,∗3A. Kim,∗12 D. H. Kim,∗6 N. Kitamura,∗2 S. Kubono,∗2,∗3 M. S. Kwag,∗6 S. Michimasa,∗2 M. Mihara,∗3,∗13H. Miyatake,∗11 S. Ota,∗2 R. G. Pizzone,∗7 H. Shimizu,∗2,∗3 N. K. Uyen,∗6 R. Wakabayashi,∗3,∗13Y. X. Watanabe,∗11 O. Wieland,∗4 H. Yamaguchi,∗2 L. Yang,∗2 N. Zhang,∗2,∗14 and Z. C. Zhang∗14
Cross section (mb)

The 8 Li(α, n)11 B reaction is considered to be thekey reaction in the inhomogeneous Big Bang and typeII supernova nucleosyntheses, and we have been providing cross-section data1–7) on this reaction for morethan two decades. The previous results1–7) are summarized in Fig. 1, in which the Gamow-peak widths
are also drawn. The energy regions of T9 = 1 and 2
are important for the Big Bang and supernova nucleosyntheses, respectively.
As shown in Fig. 1, the cross-sections obtained by
the previous experiments have large diﬀerences around
Ecm = 1.0 MeV. The previous experiments were performed by two diﬀerent methods: inclusive and exclusive. The former detected either 11 B1,2) or neutron4,6)
and the latter3,5,7) detected both 11 B and neutron bymeasuring their kinetic energies and angles. The crosssections of the former results are ﬁve times larger thanthe latter ones systematically. We could estimate thatthe sources of the discrepancies might originate fromthe experimental methods, but we have no experimental fact to determine them. To solve this problem, we
designed a new inclusive measurement, in which wemeasured the γ-rays emitted from 11 B∗ s. The previous
experiment did not measure the γ-rays. Therefore thisexperiment will provide new data to understand the8Li(α, n)11 B reaction. Considering that the expected
γ-ray energies are between 2 and 8 MeV, we selecteda large volume 3.5“×8” LaBr3 :Ce detector8) provided
by INFN Milano. We also installed plastic and 6 Li-800
T 9 =2700

T 9 =1600

Boyd1)
Gu2)
Mizoi3)Cherubini4)
Ishiyama5)
Cognata6)
DAS7)

500

400

300

200

100

00

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.82

Ecm (MeV)
Fig. 1. Excitation functions of 8 Li(α, n)11 B reaction.

glass scintillators to detect neutrons by covering wide
energy ranges between a few ten keV to 10 MeV.
This experiment was performed at CRIB in September 2018. We placed a gas-target cell at F3, in which4He gas was ﬁlled at a pressure of 1.0 atm. The 8 Li
beam, whose intensity was typically 300 kHz, was produced by the 7 Li(d, p)8 Li reaction. The primary 7 Li
beam had an energy of 6.0 MeV/nucleon and an intensity of 250 particle nA. The D2 -gas production target
had a thickness of 1.9 mg/cm2 . The energies of 8 Li
particles measured inside the 4 He-gas target were between Ecm = 0.9 and 1.9 MeV.
We successfully obtained data with suﬃcient statistics. Although we faced diﬃculties in data analysis owing to the large background originating from thermal
neutrons, we could identify the γ-rays emitted from11 ∗B s. We will further present the results to solve thecontroversial discrepancies.

∗1Center for Physics and Mathematics, Institute for Liberal
Arts and Sciences, Osaka Electro-Communication University∗2 Center for Nuclear Study, the University of Tokyo∗3 RIKEN Nishina Center∗4 Istituto Nazionale di Fisica Nucleare (INFN) - Sezione diMilano∗5 Dipartimento di Fisica dell’Università degli Studi di Milano∗6 Department of Physics, Sungkyunkwan University∗7 Istituto Nazionale di Fisica Nucleare (INFN) - Laboratori
Nazionali del Sud (LNS)∗8 Dipartimento di Fisica ed Astronomia, Università di Catania∗9 Department of Physics and Astronomy, Seoul National University∗10 Research Center for Nuclear Physics (RCNP), Osaka University∗11 Wako Nuclear Science Center (WNSC), Institute of Particle and Nuclear Studies (IPNS), High Energy Accelerator
Research Organization (KEK)∗12 Department of Physics, Ewha Womans University∗13 Department of Physics, Osaka University∗14 Institute of Modern Physics (IMP), Chinese Academy of Science (CAS)

References

1) R. N. Boyd et al., Phys. Rev. Lett. 68, 1283 (1992).
2) X. Gu et al., Phys. Lett. B 343, 31 (1995).
3) Y. Mizoi et al., Phys. Rev. C 62, 065801 (2000).
4) S. Cherubini et al., Eur. Phys. J. 20, 355 (2004).
5) H. Ishiyama et al., Phys. Lett. B 640, 82 (2006).
6) M. La Cognata et al., Phys. Lett. B 664, 157 (2008).
7) S. K. Das et al., Phys. Rev. C 95, 055805 (2017).
8) A. Gaiz et al., Nucl. Instrum. Methods Phys. Res. A729, 910 (2013).

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