RIKEN Accel. Prog. Rep. 50 (2017)

Ⅱ-9. Instrumentation

Measurement of light charged particle in the SAMURAI magnet gap
with NINJA
∗2
∗2
∗2
∗1
∗1
∗1
∗2
∗1,∗2
T. Y. Saito,∗1
N. Chiga,
Chiga,∗2
T. Isobe,
Isobe,∗2
R. Tamura,
Tamura,∗1
M. Usami,
Usami,∗1
R. Higuchi,
Higuchi,∗1and H.
H. Otsu
Otsu∗2
N.
T.
R.
M.
R.
and∗1
∗2

Department of Physics, the University of Tokyo
RIKEN Nishina Center- 178 -140

1001204He

3

ToT [ns]80

He1006080604040

2H2020103035H404550 55 60
Time [ns]657075800Fig. 1. Particle identiﬁcation with NINJA. The horizontal
axis represents the time of ﬂight between F13 plasticand NINJA, and the vertical axis represents the ToTvalue for ΔE.

145101210Y [layer]

SAMURAI is a large-acceptance magnetic spectrometer aiming at coincidence measurements of charged
particles and neutrons. SAMURAI has a standard detector setup for measuring heavy residual nuclei andneutrons, but it is practically impossible to measure
more than three types of particles that have considerably diﬀerent magnetic rigidities, such as neutrons,
heavy residual nuclei, and protons. NINJA was designed to measure protons in their trajectory inside theSAMURAI vacuum chamber before they are incident
on the side yoke of the dipole magnet.
NINJA consists of a 2-layer plastic scintillator witha thickness of 10 mm each and has a sensitive area of1080 × 720 mm2 . Multi-pixel photon counters (MPPCs) located in the pole gap of the dipole magnet areused to count scintillation photons in a strong magnetic ﬁeld.1) Signals from each MPPC are read by theVME-EASIROC frontend board,2) which equips an onboard TDC and voltage sensitive ADC.
The ﬁrst online performance test of NINJA usingprotons and other fragments was performed at RIBFin 2015. Proton beams with energies of 110 MeV and250 MeV generated by the fragmentation of a primarybeam of 48 Ca irradiated NINJA. A particle identiﬁcation (PID) test using NINJA for light fragments suchas deuterons and 3 He produced at reactions between
a secondary beam of 29 Ne and a liquid H2 target wasalso performed.
In the present experiments, it was found that thedata aquisition with the ADC remained to be developed. For the PID of light-charged ions, time overthreshold (ToT) values were taken by the TDC insteadof ADC. Figure 1 shows PID using the ToT value andthe leading edge timing of a certain bar in the X layer
measured by a plastic scintillator (F13 plastic) during
the 29 Ne+H2 run. One can clearly identify the proton,
deuteron, 3 He, and 4 He by means of TOF-ΔE.
One can measure the X and Y positions of the lightcharged particle by taking the coincidence between theX layer and Y layer. Figure 2 shows the position of a250-MeV proton beam measued by NINJA. Each pixelin Fig. 2 represents the coincidence of both layers.
The peak position is consistent with a calculation ofthe proton trajectory.
Currentry, VME-EASIROC used in the present experiments is being replaced by NIM-EASIROC aiming
at the easier handling of bias supply and low noise.
The performance with NIM-EASIROC is reported inRef. 3.
3).Further
Furtherdevelopments
developmentsare
are inin progress
progress to incor-10483106102410200246810X [layer]

12141618201Fig. 2. Measured position of a proton beam with an energyof 250 MeV.

porate NINJA into standard detectors of SAMURAI.
This work was funded by the ImPACT Program ofthe Council for Science, Technology and Innovation(Cabinet Oﬃce, Government of Japan).
References
1) N. Chiga et al.: RIKEN Accel. Prog. Rep. 49 (2015)165.
2) T. Shiozaki: Master’s thesis, Tohoku University (2014).
3) N. Chiga et al.: In this report.