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The linearity of R7400 PMT(Hamamatsu) for GSO light output is very important to secure the dynamic range from 100 GeV to 7 TeV, and it was tested at HIMAC in 2010.•By using aluminum degrader, the light output of the GSO scintillator was measured for various impinging ion energies and high voltages to the test PMT. In this experiment, 132Xe ion with the energy of 290 MeV/u were used.• As a result R7400PMT have a good linearity within +-1% up to the signal level correspond to 3TeV EM shower maximum energy deposit in LHCf calorimeter. • For the run of √s = 14 TeV in LHC, we have to check linearity up to more large signal.

1Kentaro KAWADE, 2Takuya SUZUKI1STEL Nagoya Univ. 2Waseda Univ. for the LHCf collaboration

Study of GSO scintillator for LHCf upgrade

To upgrade the LHCf, using GSO scintillator will be used because of high radiation hardness and fast decay time, large light output. We have examined the feature of GSO scintillator by using heavy ion beam at Heavy Ion Medical Accelerator in Chiba "HIMAC". We measured the linearity of R7400 PMT for large light yield with Xe ions, and the radiation hardness with C ions. As a results GSO scintillator shows good linearity up to the signal corresponding to 3.5TeV shower maximum in LHCf detector, and has good radiation hardness up to 106 Gy.

Abstract

About the LHCf experiment?

Weak point and Upgrade by GSO

GSO is a crystal scintillator with very high density. The feature of GSO fast decay time, large light output are useful for LHCf detector, and it’s extremely strong for the exposure of radiation.

The LHCf physics goal is to provide crucial calibration point for the hadron interaction models used in the cosmic-ray physics. In the LHCf experiment, We measure photons and neutral particles from the interaction point 1 "IP1" in order to verify the hadron interaction models used in very high energy cosmic-ray interaction.

Summaryn The characteristic feature of GSO scintillator was examined.n The linearity of R7400 PMT was confirmed within ±1% up to the signal level correspond to

3TeV shower maximum in the LHCf detector.n After exposure of ~106Gy, the light yield of GSO was not decreased.n In conclusion, GSO scintillator is usefull for LHCf detector.

Linearity of R7400 PMT

Radiation hardness of GSO

SciFi to GSO bar

Position dependence of GSO bar

The radiation hardness of GSO scintillator was tested at HIMAC in Nov 2010 by using 12C ion beam with the energy of 290 MeV/u.For the dose meters an ion chamber with two 2 mm air gaps was used. Irradiation was done over two nights(9.Nov & 10.Nov). The irradiation scheme was increasing rate for fist night and constant high rate for second night. Two GSO scintillators(32mm ×32mm × 1mm thick) were tested one was placed at beam axis, and the other was placed at apart from beam axis. The method of evaluation of radiation hardness are to see the response to very low intensity 12C beam fot each GSO samples. To compare both GSO samples, it can measured the radiation hardness of GSO. The response to excitation by the Xe flash lamp(337 (±10) nm UV light) was also measured.The size of beam was measured by profile monitor, and it was shown in right figure.

Very small GSO scintillators (GSO bar) have been manufactured to replace Scintillation Fibers (SciFi). For Small (Large) Tower GSO bar is 20mm (40mm) long and has 1mm square cross-section. A prototype belt using 5 GSO bars(40mm long) has been made to evaluate the light yield and position dependency at HIMAC in November 2010. Each GSO bar is connected with optical cement to a 0.7mm diameter silica fused fiber(Polymicro FVP600660710). The fibers are attached to a 64 anodes MAPMT(HAMAMATSU H7546). C beam (290MeV/n) has been injected in the length direction of GSO bars. To evaluate the position dependency 2 trigger scintillators were fixed and the GSO belts were placed on a sliding table.

図 4.13: Scinti-Damageの測定結果。横軸は吸収線量 (Gy)を logスケールで示している。範囲は 10−4～103Gy。縦軸は発光率 (%)を示している。黒の◯はDATE 1のデータ、赤の×はDATE 2のデータ、青の△はDATE 3のデータを表す。図中の 2本のラインは、上がGain110(%)、下が Gain90(%)を示している。

52

GSO scintillator(Gd2SiO5:Ce 1.5%)

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Figure 12. Photo of the SciFi hodoscope glued on the acrylic frame. Left and right parts are single ho-

doscope planes of 40mm and 20mm calorimeters, respectively.

n-type wafer. A sequence of 768 p+ microstrips with 80 µm pitch is implanted on the junction side.

The PACE3 chip, a 32 ch device designed to work with the LHC 40MHz clock and produced for the

CMS Silicon Preshower Detector [14], has been chosen for the front-end read-out. With a properly

adjusted working point, the chips have a high dynamic range (up to 600MIPs with a maximum

deviation from linearity of 6%). Due to the limited space inside the TAN and the small Moliere

radius in tungsten, we decided to read out every other strip; the read-out pitch is hence 160 µm.

In this way we have a total of 384 channels for each silicon sensor (12 PACE3 chips, housed on

two printed circuit boards). The silicon sensor is glued on a thin fiberglass fan-out circuit that is

also used to provide bias to the sensor through its backplane by means of a conducting glue [15].

Microstrips on the silicon sensors have been wire-bonded to the fan-out lines in the clean room

of INFN-Florence. The front-end electronics are glued to dedicated kapton fan-out circuits, that

in turn are wire-bonded to the boards and to the fiberglass circuit, as shown in Figure-13. Each

tracking layer is then glued on a 0.5mm thick aluminum layer (used for mechanical support) and

covered by a black Delrin frame on the silicon and by a 8.5mm thick aluminum frame on the

circuitry part. This metal frame is also used to extract the heat produced by the chips (silicon front-

end circuits dissipate approximately 60W in total) by means of a good thermal contact with the

thick copper wall used in the detector package of detector 2.

2.5 Manipulator

The manipulators move the detectors in the vertical direction in order to increase the range of

PT coverage as well as to retract the detectors from the beam line to avoid unnecessary radiation

damage when data is not being taken. The manipulators can be operated remotely. Considering the

limited access to the TAN area and its high radiation environment, the manipulators were designed

to be as robust as possible to avoid any mechanical trouble during LHC operation. A DC motor is

driven by DC power supplied from the control room. The movement direction is determined by the

– 13 –

Figure 2.13: Photos of R7400U and a EJ260 scintillator connected to a light guide.

FANOUT module (Technoland Co.;N-SE820iP) into 2 outputs with amplification factor of1 and 4. The output signals with lower gain (!1) are fed to charge-sensitive ADCs (CAEN;V965). The ADC has dual simultaneous range of 0-800pC and 0-100pC, and 12bitsresolution with 15bits dynamic range for each of the 16 channel inputs. The output signalswith higher gain (!4) are discriminated by discriminators (CAEN; V814B) to provide aDAQ trigger. The typical threshold is set to be 10mV, corresponding to 330MIPs. It ismuch higher than the electric noise level of about ±2mV on each discriminator input. Thepedestal fluctuation of each ADC channel due to the electric noise is about 20 ADC counts,corresponding to 60MIPs at the PMT gain for typical operations. It is not negligible atthe energy reconstruction for low energy gamma-ray less than a few hundreds GeV. Tomeasure low energy gamma-ray spectra with high precision, we will additionally haveoperations with 5 times lower gain for the PMTs than the normal operations. Operationswith the normal gain (" 2 ! 103) and the 5 times higher gain (" 104) for the PMTs arereferred as “the low gain mode” and “the high gain mode”, respectively. At the high gainmode, the dynamic range of the energy reconstruction for gamma-rays is limited by thedynamic range of the ADCs to less than 2TeV.

Light collection e!ciency

Because of the light guide geometry, the light collection e!ciency has position depen-dence. The position dependence of the light collection e!ciency of each scintillator wasmeasured at 4mm grid position by a 90Sr !-ray source with a 15mm thickness aluminumcollimator with a 2mm diameter hole before the detector assembly. By fitting the resultswith the 3 order polynomial function in two dimensions, the collection e!ciency was es-timated as a function of the position over the scintillator. Figure 2.15 shows measuredcollection e!ciency of typical 20mm and 40mm scintillators. The non-uniformity is about± 5% for all 20mm scintillators and about ± 20% for all 40mm scintillators. The light col-lection e!ciency of 25mm and 32mm scintillators is similar to that of 20mm scintillatorsbecause of the similar structure of the light guide.

24

20mm

20mm

The current version of the LHCf detector consists of EJ260 plastic scintillators(The characteristic features of the EJ260 scintillators was examined by C ions at HIMAC at 2007 as shown in Fig.2), and we measured the data of 7TeV collision in LHC with a present detector. According to this result, the light output of the EJ260 scintillator was decreased to 90% after the exposure corresponding to a few hundred Gy. For higher energy of LHC collisions planned in after 2013, we are developing a detector by using GSO scintillators (Gd2SiO5: Ce doped 1.5%). We have done the experiments to test the GSO scintillators as calorimeter material and position sensor.

year 201020102010 2011 2012 2013201320132013 2014

LHC √s=7TeV√s=7TeV√s=7TeV√s=7TeV Technical topTechnical topTechnical top 14TeV14TeV14TeV

LHCf Run R&D for upgradeR&D for upgradeR&D for upgrade Run

The run schedule of LHC & LHCf

beam axis

Trriger i

Trriger ii

GSO

H1161 PMTR7400

Degrader

Trriger iii

EJ260GSO

600 800 1000 1200 1400 1600 1800 20001000

1500

2000

2500

3000

3500

Graph

600 800 1000 1200 1400 1600 1800 2000

-1

-0.5

0

0.5

1

Graph

H64

10 P

MT

out

put

5 GSO bars

GSO30ns

This is the wave shape of GSO light output as response to N2 laser. Wave shape of GSO is fast enough for LHCf.

acrylic Light guide

Fig.4. Experimental setup

Fig.2. EJ260 Light yield

beam axis

optical Fiber

H1161

H1161

Ion chamber as particle counter

shade H1161

movable stage

UV Filter

shade

Dose[Gy]210 310 410 510

Rela

tive

GSo

Lig

htyi

led

1

1.05

1.1

1.15

1.2

1.25

GSO vs Dose

Residual [%]

Fig.6. Experimental setup (C ion)

R7400 PMTHamamatsu

Xe

Flas

h la

mp

LHCf have finished data taking successfully at √s=7.0 TeV, and uninstalled detectors in this july.LHC plan to technical stop for upgrade to √s=14TeV, LHCf also upgrade for higher energy collision. The R&D for upgrade with GSO scintillator is on going.

GSO EJ-260

desity(g/cm3) 6.71 1.023

r.l.(cm) 1.38 14.2

Total r.l. LHCf with PSL 1.96 0.39

wave shape(ns) 30-60 9.6

light yield(NaI=100) 20 19.6

λem(nm) 430 490

optical index(@λem) 1.85 ーradiationhardness(Gy) 106 100

SciFi Position sensitive layers are also replace to GSO detector.

GSO bars

SciFi

2 4 6 8 10

0.95

1

1.05

1.1

1.15

1.2

1.25

1.3

GSO_L vs GSO_R

exposed GSO

NOT exposed GSO

Fig.5. relative light output of GSO vs Dose[Gy]

Data of beam profile monitor

2010年12月8日水曜日