Ⅱ-1. Nuclear Physics

7RIKEN Accel. Prog. Rep. 50 (2017)

Be(n, p)7 Li and 7 Be(n, α)4 He reaction measurements at CRIB using
the Trojan Horse method

S. Hayakawa,∗1 K. Abe,∗1 O. Beliuskina,∗1 S. M. Cha,∗2 K. Y. Chae,∗2 S. Cherubini,∗3,∗4 P. Figuera,∗3,∗4Z. Ge,∗5 M. Gulino,∗3,∗6 J. Hu,∗7 A. Inoue,∗8 N. Iwasa,∗5,∗9 D. Kahl,∗10 A. Kim,∗11 D. H. Kim,∗11 G. Kiss,∗5S. Kubono,∗1,∗5,∗7 M. La Cognata,∗3 M. La Commara,∗12,∗13 L. Lamia,∗4 M. Lattuada,∗3,∗4 E. J. Lee,∗2J. Y. Moon,∗14 S. Palmerini,∗15,∗16 C. Parascandolo,∗13 S. Y. Park,∗11 D. Pierroutsakou,∗13 R. G. Pizzone,∗3,∗4G. G. Rapisarda,∗3 S. Romano,∗3,∗4 H. Shimizu,∗1 C. Spitaleri,∗3,∗4 X. D. Tang,∗7 O. Trippella,∗15,∗16
A. Tumino,∗3,∗6 P. Vi,∗5 H. Yamaguchi,∗1 L. Yang,∗1 and N. T. Zhang∗7
It has been known that the primordial 7 Li abundance predicted by the standard Big-Bang Nucleosynthesis (BBN) model1) is about three times larger thanthe observation, which is the cosmological 7 Li problem. The 7 Be(n, p)7 Li reaction is considered as themain process to destruct 7 Be during the BBN, whichis also crucial in determining the 7 Li abundance. Theresonance structure of the 7 Be(n, p)7 Li reaction was
well investigated by the R-matrix analysis2) on several
experimental data. However, the contribution of thetransition to the ﬁrst excited state of 7 Li at the BBN
energies (∼ 25 keV–1 MeV) has never been discussed.
The other interesting reaction channel of the neutron
induced reaction, 7 Be(n, α)4 He, has not been investigated until recently3,4) in terms of the relevance to theBBN scenario. Note that the new measurement4) was
limited and carried out at very low energies, which thus
lacks the information on the total 7 Be(n, α)4 He crosssection in the BBN energy region.
We performed indirect measurements of the7Be(n, p)7 Li and 7 Be(n, α)4 He reactions simultaneously by the Trojan horse method (THM)5) at the Center for Nuclear Study Radioactive Ion Beam (CRIB)
separator6) . The THM is an indirect technique thatallows us to approach a two-body reaction at astrophysical energies via a three-body reaction by selecting
the quasi-free (QF) kinematics. Moreover, the THM
is useful as a “virtual neutron source” for neutroninduced reactions by using a deuteron target7) . Similar to the ﬁrst application of THM to the RI+n reaction8) , which was performed in collaboration with
our group, we used a 7 Be beam and a deuteron targetFig. 1. Q-value spectra of the 7 Be(d,7 Lip)1 H (left) and the7Be(d, αα)1 H (right) reactions.

that induce the 7 Be(d,7 Lip)1 H and 7 Be(d, αα)1 H reactions in inverse kinematics to study the 7 Be(n, p)7 Li
and 7 Be(n, α)4 He reactions, respectively. We produceda 7 Be beam at 22.1±0.14 MeV with an intensity of1×106 pps on target. The experimental setup consistedof two parallel-plate avalanche counters (PPACs) for
beam tracking, a CD2 target, and six ΔE-E positionsensitive silicon-detector telescopes at ±12◦ , ±34◦ and±56◦ . The thickness of the CD2 target was 64 μg/cm2 .
A use of such a thin target allows reducing the energy
spread to about 120 keV. This helps to identify theﬁrst excited state of 7 Li (478 keV) in the reconstructed
Q-value spectrum. We observed p-7 Li and α-α coincidental events, and conﬁrmed that they were kinematically correct as the expected three-body exit channels.
Figure 1 shows three-body Q-value spectra of thosechannels. The peaks are ﬁtted by Gaussian functions
with mean values of -0.67 MeV and 16.64 MeV, respectively, which are consistent with the known Q values of-0.580 MeV and 16.766 MeV within the resolution ofabout 600 keV (rms). This resolution is expected to beimproved to 150–200 keV with more precise energy andangular calibrations and further corrections. Accordingly, one can resolve both the ground and the ﬁrst
excited state of 7 Li. By selecting the corresponding
kinematic region, we estimate about 3000 QF events
for the 7 Be(n, p)7 Li channel in total.

∗1Center for Nuclear Study, University of Tokyo
Department of Physics, Sungkyunkwan University∗3 Istituto Nazionale di Fisica Nucleare - Laboratori Nazionalidel Sud∗4 Department of Physics and Astronomy, Univ. of Catania∗5 RIKEN Nishina Center∗6 Faculty of Engineering and Architecture, Kore Univ. of Enna
∗7 Institute of Modern Physics, Chinese Academy of Sciences∗8 Research Center for Nuclear Physics, Osaka University∗9 Department of Physics, Tohoku University∗10 School of Physics and Astronomy, University of Edinburgh∗11 Department of Physics, Ewha Womans University∗12 Depart. of Phys. ’E. Pancini’, Univ. of Naples Federico II∗13 Istituto Nazionale di Fisica Nucleare - Section of Naples∗14 High Energy Accelerator Research Organization (KEK)∗15 Istituto Nazionale di Fisica Nucleare - Section of Perugia∗16 Department of Physics and Geology, University of Perugia∗2References
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2) A. Adahchour and P. Descouvemont, J. Phys. G 29,395 (2003).
3) S. Q. Hou et al., Phys. Rev. C 91, 055802 (2015).
4) M. Barbagallo et al., Phys. Rev. Lett. 117, 152701 (2016).
5) C. Spitaleri et al., Phys. Atom. Nucl. 74, 1725 (2011).
6) Y. Yanagisawa et al., Nucl. Instrum. and Meth. A 539, 74(2005).
7) M. Gulino et al., Phys. Rev. C 87, 012801 (2013).
8) L. Lamia et al., Proc. 14th International Symposium onNuclei in the Cosmos, JPS Conf. Proc., in publication.
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