DEVELOPMENT OF THIN PLASTIC SCINTILLATION COUNTER FORLOW ENERGY MUON EXPERIMENT AT MuSIC
I.H.Hashim1, 2, Y.Kuno1, A.Sato1, Y.Hino1, H. Sakamoto1, Y.Matsumoto1.
12

Graduate School of Science, Osaka University, Toyonaka, 560-0043 Osaka, Japan.
Departments of Physics, Faculty of Science, Universiti Teknologi Malaysia, 81310
Johor Bahru.

Abstract:MuSIC is a highly intense muon facility which was constructed at RCNP, Osaka University andofficially operated since 2009. MuSIC was equipped with a superconducting solenoid at the pion
capture system a muon yield up to 108 muons /sec is available. The thin counters with dimension of30 mm x 380 mm x 0.5 mm has been developed for low energy muon experiment at the MuSIC 5th
beam test. Each counter was attached with a wavelength shifting fiber (WLS) and MPPC for
readout. Several tests and experiments were done in order to achieve best position resolution withthin plastic scintillation counter for medium energy muon experiment.
1.

INTRODUCTION

MuSIC facility at RCNP, Osaka University can yield
about 108 muons per sec and which equivalent to thehighest intensity in the world, and a broad field of muonscience can be carried out with the muon beam provided
by the MuSIC. The MuSIC consists of two systems which
are a pion capture system and muon transport system
which officially operated since 2010 [1-3]. A 0.4kW
proton beam produced by a cyclotron is injected on agraphite target in the pion capture section. The pions yield
will be transport by the muon transport solenoid of 2
Tesla solenoidal magnetic fields. In addition, the dipole
field may provides charge and momentum selection of themuon beam.

MuSIC provides variety of muon experiments such as
muon lifetime measurement and muonic X-ray
measurement. From the first until 4th beam test, these two
measurements were taken using the medium energy muon.
In the 5th beam test last June, muon energy and spatial
distribution was measured. The muon beam in MuSIC is a
DC muon source; we hardly get the timing information
for the muon arrival time from the accelerator systemsuch as RF timing. The trigger counter was essential toobtain the time information and location information
during the MuSIC experiments. Due to low energy muons
stopped on a target, the thin plastic scintillation counterswere used as the trigger counter in order to avoid low
energy muons to stop on the scintillators before hit thetarget.

Beam On
Muon stopped

Figure 2: Momentum distribution in MuSIC 4th beam test
Figure 1: Schematic layout of MuSIC

The main purpose of this detector is to make a trigger
timing signal for the stopping muons. The detector is
located upstream from the stopping target. Another thickplastic counter is placed downstream from the target, and- 659 -is used as a Veto counter. Using signal from both counter,trigger signals are made for muons stopped in the target.
The trigger signal is work as start timing for the muon
lifetime measurement, and provides gates to ADC
modules for muonic X-ray measurements.
Since the solenoid was equipped with strong magnetic
field, MPPC was used as readout. MPPC have many
features which may challenge the capability andsensitivity of PMT [4]. Even though the size and its active

2.

area of MPPCs are so small compared to PMTs, it is able
to detect photon signals separately [4, 5].
The aim of this study is to measure the rate of hit ofparticle, number of light yield for each MPPC attached in
the counter and also the measurement of muon lifetime
using the designed thin plastic scintillation counter. The
combination of MPPC with Wavelength Shifting (WLS)
fiber may enhance the capability of both components todetect particle.

EXPERIMENTAL PROCEDURE(a) Self trigger

The end of solenoid exits at MuSIC was about 40cm indiameter. The thin plastic scintillation counters weredesigned to cover the exits. In this study, we develop thethin scintillation counter with the dimension of 380mm x30mm x 0.5mm. The counter was attached with thewavelength shifting fiber at the centre of the thin plastic
scintillator and the readout was Hamamatsu MPPC
S10362-13-050C.
Light yields are measured with three different locationof WLS fiber before deciding the suitable counter for theMuSIC; centre, side and edges (Refer to Figure 3(a), 3(b)and 3(c). 2 MPPCs are attached at the end of the fiber.
The number of photon yield at each MPPC will berecorded and compare for the selection of MuSIC beamtime detector. The 241Am source was used during theexperiment. All plastic scintillators were wrapped with
2µm aluminized mylar to enhance the light yieldpropagation of the fiber towards the MPPC readout.

pedestal

1 p.e
2 p.e
6 54 3 21(b) Coincidence trigger

Figure 3: Signal from MPPCWLS fiber
2µm AlPlastic Scintillator
MPPC(a) Centre(b) SideThe chosen configuration for MuSIC 5th beamtest was
finally check and the total muon yield at each MPPC wascalculated. During the beam test, a set of 8 thin plastic
scintillation counters was used. This detector was mainly
used to determine muon lifetime with few metal targets,the momentum distribution of muon also will bedetermined.
A trigger is made with coincidence of two MPPC.
MPPC signal with NIM module and observed with
LeCroy waverunner oscilloscope.

(c) Edges
Figure 2: Three Configuration of tested thin

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scintillator causing the event counted by opposite MPPC
is not evenly distributed. The centre configuration waschosen among all due to good photon yield, large signal
to noise ratio compare to other configurations and alsoeasy fabrications steps.
Figure 3(a) shows the self trigger signal of MPPC andfigure 3(b) shows the coincidence signal from MPPC with241
Am for centre configuration. The dotted line represents
the gain of the MPPC. We can estimate that the average
light yield detected at centre configuration was about 6photons.

3. DETECTOR PERFORMANCEThe MPPC has single photon counting detection, eachphoton detected by MPPC will represent by photopeak
respectively.
Table 1 below summarizes the rate of event per second
at every 2.5p.e threshold for three assigned configurations.
Dark current rate and source rate was then compared tochoose the suitable configuration. The centre and side
configurations recorded almost same events rate, however
the event for edges was slightly different from these two.
This might due to poor connection of fiber and plastic
Table 1: Rate of events for MPPC

SourceMPPC

Vop (V)

Rate@2.5pe, Iobs (kHz)

Dark current@1.5pe, Iref (kHz)CenterSide

Edges

TJ5359

71.37

57.9

15.0

15.0

8.9

TJ5362

71.38

56.7

12.3

12.1

36.5

TJ535971.3757.9

32.3

18.8

16.3

TJ5362

71.38

56.7

21.2

16.5

55.3

No241

Am

4. BEAMTEST PERFORMANCE
Eight sets of center configuration were then fabricatedand the light yields for all MPPC were measured. Figure 4
was the thin plastic scintillation counter for MuSICbeamtest. The same type of MPPC was used for allcounters. The 241Am source was placed at the center of theplastic scintillator. The gain was set to each MPPC so thatthe signal can be clearly separated from the pedestal.

The MPPC signal during the beamtest can be observe
by VME module. Figure 5 shows the signal of MPPC, ablack curve represents the raw ADC signal of MPPC andthe red curve represents the ADC signal over threshold.
We can clearly see the separation between pedestal andmuon signal with the thin plastic scintillators.
threshold

Figure 5: ADC Signal of MPPC during beam test

5. CONCLUSION

Figure 4: Thin Plastic Scintillation counter for MuSIC

In this study, we quantitatively compared the rate ofevent on three different configurations of thin plastic
scintillation counter. We also employed a coincidence
technique which effectively rejected dark noise producedby each MPPC. We found that the position of WLS fiber- 661 -and the MPPC readout do affect the event rate at each
MPPC and the coincidences of two opposite MPPC
effectively reduce the dark count.
We can conclude that the average number of photon
yield at each MPPC was about 6 photons. The separation
between photopeak also can be clearly distinguished withthis thin counter by offline and online beam experiment.
References[1] A.Sato, Y. Kuno, et al, Proceedings of IPAC2011,
EPS-AG 820 (2011).
[2] Yoshitaka Kuno. Nuclear Physics B (Proc. Suppl.)
225-227(2012)228-231.
[3] Yoshitaka Kuno, Nuclear Physics B (Proc. Suppl.)
217(2011)337-340.
[4] T. Miura, T. Nakamori, et al. THE 9th International
Conference On Position Sensitive Detectors 2011. JINST
7 C02036.
[5] Satoru Uozumi. Proceeding of LCWS 2007.

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