29th International Cosmic Ray Conference Pune (2005) 00, 001-004

Performance of the Surface Scintillation Detector for The Telescope
Array
Y. Hayashi, S.Kawakami, K.Matsumoto, Y.Matsumoto, T.Matsuyama, T.Nonaka, T.Okuda,A.Oshima, H.Tanaka and TA collaborators
Graduate School of Science, Osaka City University, Osaka 558-8585, Japan

Presenter: S.Kawakami (kawakami@sci.osaka-cu.ac.jp), jap-kawakami-S-abs1-he15-poster

Systematic measurement on basic characteristics of surface detectors have been done in detail.
These test are quite essential for reducing the systematic error in estimating the total number ofcharged particles in a giant air shower, so energy of primary cosmic rays. Some of those things,
such as position sensitivity and temperature dependence of scintillation detector and surface
sensitivity map of photo tubes were also measured. We found that all of these variation is within
10 to 15% and total performance of our scintillation systems are well inside our expectation.
1.Introduction
The temperature at Utah’s Delta county varies from around –10 degree to well over 35 degrees.
Our measurement system should give reasonable response under this severe condition and standfor long time operation, say 10 years. In order to minimize the systematic error on energy
estimation of primary ultra high energy cosmic rays the characteristics of surface scintillation
detector have to be investigated thoroughly. Most of the case MC calculation should be adopted todeduce the energy of primary cosmic rays. There are several features that causes the error, forexample, uniformity variation along with the surface of scintillator, since our SD has 3 m2 area.
Temperature dependence of SD’s out put signal is thought to be large enough to be corrected
properly. Short time variation of these PMT’s output can be monitored and corrected utilizing themonitored data such as pulse height distribution of
2.Measurements1). Uniformity variation
Schematicblock

diagramfor

uniformity measurement over thesurface of 1.5m 2 is shown in fig.1.
Their results have been shown infig.2 as relative efficiency.
The raw data were also shown in fig3.
As you can see in fig2., there might besystematic change in position sensitivity,
around 7 to 8 % deviation from average.To confirm better uniformity, we are planning to measure theiruniformity with much better

resolution.
NMWNESE600

Uniformity

South → North
500

1.2

3500

3000

2500

400

1Normalized

2000
0.8300
1500

0.6

200
0.4

1000

0.2

100

5000SESMSWMEMMMWNE

NM

NW

01000

00Position

100200

300

400

500

600

700

8009002).Temperature dependence
Fig.4 shows small testing detector for temperature dependence of scintillation detector very
similar to the real one is to use as surface detector for Telescope Array
Schematic Diagram of measurement system onTemperature dependence of Sc detector system

Linear Grooves (13 grooves）

Delay (150ns)
Amp×10Sc DetectorSignal

25cm

igaTrigger
2cm

25cm
1.0cm

Amp×10

Incubator

Discriminator（‐15mV）

Project.

％

0Schematic diagram for the sameplastic scintillator, wave length shifting

Sc.1 [Linear]Sc.2 [Linear]Sc.2 [Sigma]

10Gate generator（300nsec）

is shown in Fig 5. The system consists ofTemperature coefficientof scintillation detector ％20ADC

fibers, Photo multiplier and the socket withhigh voltage power supply. Its performanceis shown in fig.6. We have completed 3‑10different arrangement in scintillator and‑20

shape of grooves. Practically there was no‑30

significant difference among these different‑40‑20‑10010203040

Temperature (℃）

5060

type of test. As you can see in fig.6,
temperature coefficient for whole detector
system is 7 to 8 % /degree centigrade. Itlooks to be rather larger than expected.
3)Overall performance of detector
Typical output pulse height distribution of proto type (1.5m 2 ) scintillation detector for throughgoing muons were shown in fig.7.

Sharp peak is for single photo electron and broad peak is for through going muons. Since quantum
efficiencies of present our PMT (1924SA) is about 25 %, it means that typically about 80 photons
are collected along with wave length shifting fibers for through going muons.
PMT‑45808<<DATA>>

PMT‑33524

2000
1800
1600
1400
1200
1000
800
600
400
20001000
800
600
40020000200

400

600

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<<DATA>>

Pulse height Distribution

1200

1200

1400

1600

1800

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0200

400

600

800

1000

1200

1400

1600

ADC Bin#

ADC Bin#(4)Position sensitivity of PMT
We measured the position sensitivity of Cathode surface of Photo Multiplier Tubes.
The schematic view and its block diagram of measuring systems are shown in fig,8.
See typical sensitivity distribution in fig.9. The histogram in fig.10 shows preliminary results

X

30

28

2624

2220

18

16

14

12

8

10

6

4

20

about sample variance of Cathode surface sensitivity, only for 21 PMTs.

25397

Variances of Cathode surface
sensitivity

6115-120110-115105-110100-105
95-100
90-95
85-90
80-85
75-80

Number of samples

30
29
28
27
26
25
24
23
22
21
20
19
18
17
1615 Y
1413
1211
10
987654321054321004080 120 160 200 240 280 320 360 400 440 480

Sample variance3.Summary
We have performed quite intensive investigation on detailed characteristics of proto typesurfacr scintillation detector for Telescope Array Project. What we have got is quite useful for
conducting detector simulations and without such information one cannot be confident with theirresults. Same time these results are quite satisfactory for conducting the Giant Air Shower
observation on the whole. But we feel some of the characters and behaviors have to be checked up
still.
4.Acknowledements
Authors are grateful to Prof. S.C.Tonwar and S.K.Gupta of Tata Institute of Fundamental
Research for their support to design the proto type detector and useful comments anddiscussion on measurements.
Reference