RIKEN Accel. Prog. Rep. 48 (2015)

Ⅱ-9. Instrumentation

NiGIRI: Identification of n, p, d, t, 3,4He, 6,7Li, and γ-rays†
H. Matsuzawa,∗1,∗2 S. Nishimura,∗2 T. Isobe,∗2 G. Lorusso,∗2 M. Kurata-Nishimura,∗2 and K. Ieki∗1The azimuthal angle correlation of neutrons andcharged particles with respect to the reaction plane inheavy-ion collisions is expected to provide essential information on the equation of state (EOS) of high density nuclear matter in supernovae and neutron star.
A new scintillation detector NiGIRI (Neutron, ion,and γ-ray Identification for Radioactive Isotope beam),comprises two types of PMTs (Hamamatsu H11265200, R8520-20-12) attached on both sides of a plastic
scintillator EJ299-33 (30×55×127 mm3 ), is designed tomeasure the positions and energies of neutrons (≥ 100keV) and charged particles (π ± , p, d, t, 3,4 He, 6,7 Li, ..)with pulse-shape discrimination (PSD) capability1–3) .
A feasiblity study of the NiGIRI detectors was performed using 132 Xe + CsI collisions at energies of400 AMeV at HIMAC. The energies and positions ofcharged particles were reconstructed and identified using the correlations of energy losses (∆E), timings, andPSDs among the different layers of NiGIRI detectors.
Sixty four signals (32 NiGIRI detectors x 2 PMTs),
recorded with a synchronized wave-dump mode of four
flash ADC modules (CAEN V1730B; 500 MHz with 14bits), were analyzed to deduce the integrated charge,timing, and PSD offline.
Figure 1 demonstrates the particle identification of
low energy p, d, t, 3,4 He, and 6,7 Li in the energy correlation of the 1st layer of NiGIRI (E) and a chargedparticle veto plastic scintillator (CPV: 2 mmt ; ∆E).
The punch-through charged particles with higher energy were identified using up to 8 layers of NiGIRI
detectors.

Fig. 1. Correlation between the veto counter (∆E) and 1stlayer (E).

Particle identification of neutrons was tested using
the PSD, which is the ratio of the total charge-integral(gate width = 385 ns) and tail charge-integral (gatewidth = 360 ns; delay = 24 ns) of each PMT signal. The energy dependences of the PSD for charged∗1∗2

Department of Physics, Rikkyo Univ.
RIKEN Nishina Centerparticles (Fig. 2a: events with CPV signal) and neutral particles (Fig. 2b: events with no CPV signal)
show separation of particles among (p-d-t)-(He)-(Li)and (γ)-(n), respectively. The energies of these ionscan be deduced using the time-of-flight (TOF) between
the CsI target and the NiGIRI detectors, which is also
useful for the consistency check with the energy losses
in the NiGIRI detectors. π ± production can also bestudied by tagging stopped π decays in wave-dump
signals of the last NiGIRI detector.

Fig. 2. PSD of the 1st layer main PMT of charged particles(a) and neutrons and γ-rays (b). Charged particle after
CP veto in (b) is simply due to insufficient coverage of
the NiGIRI detector.

Figure 3 shows the proto-type NiGIRI arrays arranged with full azimuthal coverage. Upgraded NiGIR detectors will be applied at RIBF to study theneutron-proton differencial flow at target rapidity inneutron-rich nucleus collisions, where reaction plane
will be determined by measuring the squeeze-out outof-plane flow in mid-rapidity region.

Fig. 3. Thirty two NiGIRI detectors (16 arrays x 2 layers) arranged at target rapidity for multiplicity measurement.

References
1) S.A. Pozzi et al.; Nucl. Instr. Meth. A 723, 19-23 (2013)2) S. Nyibule et al.; Nucl. Instr. Meth. A 728, 36-39 (2013)3) H. Matsuzawa et al.; RIKEN Accel. Prog. Rep. 47(2015)- 212 -完全版2014_本文.indd 212

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