Ⅱ-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 52 (2019)

Gamow-Teller transitions in 6 He with PANDORA
L. Stuhl,∗1,∗2 J. Gao,∗2,∗3 M. Sasano,∗2 K. Yako,∗1 Y. Kubota,∗2 Z. Yang,∗2 J. Zenihiro,∗2 V. Panin,∗2Z. Korkulu,∗2 E. Takada,∗4 H. Baba,∗2 and T. Uesaka∗2We started a program at RIBF aiming to study thespin-isospin responses of light drip line nuclei. An experiment1) with 5 days of beam time was approved toinvestigate 11 Li and 14 Be nuclei. The charge-exchange(p, n) reactions at intermediate beam energies (E/A >100 MeV) and small angles can selectively excite theGamow-Teller (GT) states up to high excitation energies
in the ﬁnal nucleus. Therefore, (p, n) reactions in inverse
kinematics applying the missing mass reconstruction2,3)
provide the best and eﬃcient tool to study the B(GT)strength values of unstable isotopes in a wide excitationenergy region, without Q-value limitation. In a pilot
measurement of the mentioned experiment, we studied
the case of 6 He at HIMAC facility in Chiba to investigate the Gamow-Teller transitions in 6 He and commission our new plastic scintillator-based neutron detector PANDORA (Particle Analyzer Neutron Detector
Of Real-time Acquisition)4) and its pulse shape discrimination (PSD) capability.
The secondary beam properties and details of the experimental setup are described in another contribution
in this volume.5) By using PANDORA with our digital
data acquisition system,6) we could detect the neutrons
having kinetic energies of a few tens of keV. Neutronand gamma-like events could be separated by deﬁning
PSDmean value as the arithmetic mean of PSD values1)of two single-end read-outs of each bar. From the measured neutron time-of-ﬂight and recoil angle (in the laboratory angle range of 75◦ –99◦ ), the excitation energyof the residual nucleus can be reconstructed. Figure 1
shows the calculated kinematical correlations for the6He(p, n) charge-exchange reaction at 123 MeV/nucleon

Fig. 2. Neutron spectra as functions of both recoil neutronenergy and recoil angle in the 6 He(p, n) reaction without gating on neutron-like events (a) and with gate onneutron-like events (b).

energy.
Selecting the incident 6 He particles and the identiﬁcation of 6 Li reaction residue produced from the (p, n) reaction, a clear kinematical correlation can be seen on theFig. 2 (a) scatter plot. This matches with the calculated
curve and corresponds to transitions to the ground statein 6 Li. After gating on neutron-like events by PSDmean ,the improvement of the kinematic locus in Fig. 2 (b)presents the eﬀectiveness of PANDORA and its PSD capability. The data shown here were accumulated within
9 h. Further analysis with larger statistics is in progress.
This work was supported by KAKENHI 16H06716
and the Japan Society for the Promotion of Science.
ReferencesFig. 1. Correlations between recoil neutron energy and laboratory kinematics for fixed excitation energies.
∗1
∗2
∗3
∗4

Center for Nuclear Study, University of Tokyo
RIKEN Nishina Center
School of Physics, Peking University
National Institute of Radiological Sciences (NIRS)- 60 -

1) L. Stuhl et al., RIKEN Accel. Prog. Rep. 48, 54 (2015).
2) M. Sasano et al., Phys. Rev. Lett. 107, 202501 (2011).
3) M. Sasano et al., Phys. Rev. C 86, 034324 (2012).
4) L. Stuhl et al., Nucl. Instrum. Methods Phys. Res. A 866,164 (2017).
5) M. Sasano et al., RIKEN Accel. Prog. Rep. 51, 78 (2018).
6) J. Gao et al., RIKEN Accel. Prog. Rep. 51, 146 (2018).