Ⅱ-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 51 (2018)

Experimental setup of the 6 He(p, n) measurement at HIMAC andidentification of the charge-exchange (p, n) reaction channel
M. Sasano,∗1 L. Stuhl,∗1,∗2 J. Gao,∗1,∗3 K. Yako,∗2 Y. Kubota,∗1 Z. Yang,∗1 J. Zenihiro,∗1 V. Panin,∗1Z. Korkulu,∗1 E. Takada,∗4 H. Baba,∗1 and T. Uesaka∗2
As reported in another article1) in this volume, we
performed a measurement of the 6 He(p, n) reaction inthe SB2 course at HIMAC in the winter of 2017 (H391experiment). In this report, the setup used in the HIMAC experiment is presented with a preliminary resultof the analysis to identify the (p, n) reaction channel.

of 96%. The particle identiﬁcation (PID) of the beam
particles was performed on an event-by-event basis byusing the energy loss information in the SBT plastic
scintillator. The secondary beam was impinged on apolyethylene target with a thickness of 7 mm. The
recoil neutrons were detected using the PANDORA2)
neutron detectors surrounding the target. The hodoscope bars were placed downstream of the target toidentify the reaction residues produced in the (p, n) reaction from the incident 6 He particles. Depending on
the excitation energy, the daughter nucleus, i.e. 6 Li,
decays into multiple reaction residues of light nuclei
such as protons, neutrons, and tritons. With the aimof distinguishing such events, the hodoscope setup consisted of three layers: the ﬁrst layer was used to identify
6Li only, while the other two layers were segmented soas to detect light nuclei. HD0 (HD1-8) had a plastic
scintillator plate with dimensions of 240W × 80H ×2D mm3 (100W × 1000H × 10D mm3 ). HD0 covered
the solid angle for 6 Li particles emitted at angles up
to 7◦ , which was suﬃcient to measure the (p, n) reaction at scattering angles up to 15◦ in the center-ofmass system. As a parasitic setup, the silicon detector
setup developed for SAMURAI heavy-ion proton experiments was also installed.
Figure 1 (bottom) shows a PID plot of reaction
residues obtained by comparing the charge informationin the hodoscope in the ﬁrst layer (HD0) and that in
the second layer immediately behind HD0 (HD2), afterselecting events corresponding to 6 He beam particles.
The data shown here were accumulated within a twohour run. The most intense PID blob corresponds tothe events in which the 6 He beam particles penetrated
both HD0 and HD2 (unreacted events). The blobaround (E0 , E1 ) = (1600, 1100) is due to the eventsin which the 6 Li beam particles penetrated both HD0and HD2, corresponding to the (p, n) reaction channel. The 6 Li events are clearly separated from the unreacted events in this two-dimensional plot. We have
an issue that the energy loss information in HD2 forthe unreacted channel has a long tail for higher QDCvalues. For clarifying the origin of this tail, we areplanning to analyze the waveform data of HD2 takenby the CAEN digtizer modules reported in another article3) in this volume. The analysis is in progress.

Fig. 1. (top) Layout of the experimental setup used in
the HIMAC H391 experiment. (bottom) Particleidentification plot of reaction residues. The vertical andhorizontal axes correspond to the energy losses in HD0and HD1 (E0 and E1 ), respectively. The units are QDCchannels.

Figure 1 (top) shows the layout of the experimental
setup. In the experiment, a secondary beam of 6 He at
123 MeV/nucleon was produced through a fragmentation reaction with a 160 MeV/nucleon primary beamof 11 B. The resulting cocktail beam had a total intensity of 2×104 particles/s, containing 6 He with a purity∗1∗2∗3∗4References
1) L. Stuhl et al., in this report.
2) L. Stuhl et al., Nucl. Instrum. Methods Phys. Res. A866, 164 (2017).
3) J. Gao et al., in this report.

RIKEN Nishina Center
Center for Nuclear Study, University of Tokyo
School of Physics, Peking University
National Institute of Radiological Sciences (NIRS)- 78 -