Ⅱ-9. Instrumentation

RIKEN Accel. Prog. Rep. 50 (2017)

Development of a monitor for stored particles in the Rare RI Ring
S. Omika,∗1,∗2 T. Yamaguchi,∗1 N. Tadano,∗1 T. Suzuki,∗1 Z. Ge,∗1,∗2 K. Wakayama,∗1 Y. Abe,∗2 T. Uesaka,∗2S. Naimi,∗2 F. Suzaki,∗2 D. Nagae,∗2 Y. Yamaguchi,∗2 M. Wakasugi,∗2 M. Amano,∗3 A. Ozawa,∗3 D. Kamioka,∗3S.
S. Suzuki,Suzuki∗3 and T. Moriguchi∗3The precise mass measurements of neutron-rich nuclei are important for the study of the r-process andnuclear structure. The Rare RI Ring is a device for the1)2)
precise mass measurements for short-lived nuclei.1,2)
In the mass measurements, the magnetic ﬁeld in thering is adjusted to be isochronous by using trim coils.
Under this condition, the revolution time is constantand independent of the momentum of particles. This
device determines the masses by comparing the revolution time of the reference particle with known massand the particle of interest. First, we must optimize
the septum magnets and the kicker magnet to enable
the injection and storage of particles. For this purpose,a detector is needed to monitor the stored particle in
the Rare RI Ring.
The required performance of a detector to conﬁrm
particle storage is high eﬃciency and low material density on beam line. In this report, we have developed adetector using a thin foil, scintillators and multi-pixel
photon counters (MPPCs). This detector detects multiple turns by detecting secondary electrons including
low-energy electrons to δ-rays using plastic scintillators and MPPCs. As a detector for the same purpose, atiming detector using a carbon foil and a micro-channel
plate has been developed.3) The advantage of the newdetector is that it is free from the electrical noise of
the kicker magnet because it uses a photo-sensor.

with 3-mm thickness. The size of plastic scintillators
on both sides is 80 ʷ 50 mm2 with 3-mm thickness. We
prepared ten MPPCs. Eight of them were connected tothe upper side of the plastic scintillator and the othertwo were connected to the left and right sides. Ten
MPPCs were divided into two units, the right half andthe left half, and signals of ﬁve MPPCs are combined
into one signal to reduce the number of readout channels. Hereafter, we refer to the developed detector as
the δ-ray detector.
In November 2016, we conducted the third machine
study of the Rare RI Ring4) and measured revolution
time using the δ-ray detector and the timing detector. In this experiment, we injected nuclei around 78 Gewith 175 MeV/nucleon. Figure 2(a) shows a histogramof the circulation of 78 Ge. This ﬁgure indicates thesuccess of detection of circulating particles. The revolution time is calculated by the relationship between
the turn numbers and total stored time (Fig. 2(b)).
The revolution time measured by the δ-ray detector isconsistent with the value measured by the timing detector. The precision of determining revolution timewas 8 ʷ 10 −4 . The future development goal is theimprovement of time resolution.

Fig. 2. (a) Zoomed histogram of the circulation of 78 Ge.
(b) Time as a function of turn number, which is ﬁt using
a linear function.
Fig. 1. Schematic view of the conﬁguration of the δ-raydetector.

Figure 1 shows a schematic view of the developed detector. The thin foil consists of 3-μm-thick aluminum.
The size of the top plastic scintillator is 100 ʷ 100 mm2∗1∗2∗3

Department of Physics, Saitama University
RIKEN Nishina Center
Institute of Physics, University of Tsukuba- 185 -References
1) A. Ozawa et al., Prog. Theor. Exp. Phys. 2012, 03C009(2012).
2) Y. Yamaguchi et al., Nucl. Instrum. Methods. Phys.
Res. B 317, 629 (2013).
3) D. Nagae et al., RIKEN Accel. Prog. Rep. 49, 181(2016).
4) D. Nagae et al., In this report.