GEM Detector

Shoji Uno

KEK

2

Wire Chamber

• Detector for charged tracks

• Popular detector in the particle physics, like a Belle-CDC

• Simple structure using thin wires

3

Gas amplification near anode wire• High electric field (>30kV/cm) can be

obtained easily due to using thin wire (diameter ~0.03mm)

• Energy of electron become higher for high electric field near wire.

• Electron can produce another electron for ionization.

• Number of electrons increases due to multi steps of this process.

　　 (gas amplification 、 electric avalanche)

• Gas gain up to ~105 can be obtained easily.

Electron

Anode wire

Recent gas chamber

• Requirement– High incident rate

• One wire covers wide region.

– Wire spacing > ~1mm

– Length >~10cm

Need more space

– Pure two-dimensional readout

– Wire has some limitation due to straight wire

LHC 　 ATLAS

Limitation of wire chamber

New development

• Development MPGD （ Micro Pattern Gas detector)– Gas multiplication in high electric field

with other than wire – 3 types

• MSGC （ Micro 　 Strip 　 Gas 　 Chamber ）• MICROMEGAS （ Micromesh 　 Gaseous 　

Detector ）• GEM （ Gas 　 Electron Multiplier ）

GEM (Gas Electron Multiplier) 　

Hole diameter 　　 70mHole pitch 　　　 140mThickness 　　 50mCu thickness 　　　 5m

Electric field

Developed by F.Sauli (CERN) in 1997.NIMA 386(1997)531

Double side flexible printed circuit board

　

GEM foil 50μm Kapton

3μm Cu

3μm Cu

Electrical field

Amplification

electrons

electron

Flexible shape

Fabio Sauli

Configuration for GEM detector

Readout

Multi-layer

High counting capability

ワイヤーチェンバー GEM

Application of GEM

• Feature of GEM– Pure two-dimensional readout 　→　 Image

– Multi-layer structure

• Stable operation

• Multi-conversion-layer (Neutral Charged)

– High counting capability

• GEM can be applied for many other fields, not only high energy physics.

TPC

X-ray detector

X-ray absorption tomography

Crystal structure analysis using X-ray

Photon sensor

• Same function for photomultiplier

• Usable in Magnetic field

• Fine segmentation in readout

• Cheap and Larger

• Key issue is photo-electric surface in gas volume.

• Under developement

Basic property of GEM chamber

Test 　 Chamber

GAS Ar-CH4(90/10) (P-10) Ar-CO2(70/30)

2200pF

2200pF～ 2 mm

10 mm

GEM1

GEM2

GEM3～ 2 mm

～ 2 mm

55Fe (5.9 keV X-ray)

DRIFT

TRANSFER 1

TRANSFER 2

INDUCTIONPCB

36 ＝ 6×6

1mm

□15mm×15mm

PCB

Pulse shape

Signal from Readout pad

Signal from GEM foil

200ns

130mV

Effective gas gain and resolution

Ar-CO2

P10

Num

ber

of e

vent

s

Sigma/Mean = 8.8%VGEM=325V

Edrift = 0.5kV/cm Etransfer = 1.6kV/cm Einduction= 3.3kV/cm

55Fe

ADC counts

Pedestal=104.6

Ar-CH4(90/10)

Gas gain vs various parameters

P10

Ar-CO2

Ar-CO2

Ar-CO2

P10

P10

Ar-CO2

EDEI

ETEI

ΔVGEM=360VET=1.6kV/cmEI=3.6kV/cm

ΔVGEM=360VET=1.6kV/cmEI=3.6kV/cm

Electric field dependence in drift region55Fe (5.9 keV X-ray)

EDＤｒｉｆｔ region

ED=3000V/cm

EI=1000V/cm

ED=500V/cm

EI=1000V/cm

In case of weak field In case of strong field

Δ ＶＧＥＭ＝３２０ＶΔ ＶＧＥＭ＝３２０Ｖ

Ionization occurs in drift region

Electrons enter into GEM holes.

Collection Efficiency

Electric field (kV/cm)

Charge distribution

AD

C c

ount

s

0 63Channel

One event

ｄ X （各 strip － C.O.G)

σ ＝ 359.7±0.4 μm

P10ΔVgem ＝３３０ V

Ed= 0.5 kV/cm

Et=1.65 kV/cmEi= 3.3 kV/cm

ΔVgem ＝３３０ V

Ed= 0.5 kV/cm

Et=1.65 kV/cmEi= 3.3 kV/cm

ADC

SUMADC

-1 0 　 1

Nor

mal

ized

AD

C c

ount

s

ｍｍ

ΔVgem ＝３７０ V

Ed= 0.5 kV/cm

Et=2.59kV/cmEi=5.18 kV/cm

ΔVgem ＝３７０ V

Ed= 0.5 kV/cm

Et=2.59kV/cmEi=5.18 kV/cm

σ ＝ 181.2±0.3 μm

Ar-CO2

(70/30)

-1 0 1

Nor

mal

ized

AD

C c

ount

s

ｄ X （各 strip － C.O.G)ｍｍ

dX (each strip – C.O.G)

dX (each strip – C.O.G)

y = 0.2979x + 0.0016

y = 0.0668x + 0.0062

0

0.05

0.1

0.15

0.2

0.25

0 0.2 0.4 0.6 0.8

Total　gap(cm)

(mm2 )

P10P10

Ar-CO2Ar-CO2

0.546mm/√cm0.546mm/√cm

0.258mm /√cm0.258mm /√cm

Charge spread

Diffusion is dominant factor.

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0 1 2 3 4

V/ cm)電場（ｋ

σ2 (mm

2 )

P10P10

Ar-CO2Ar-CO2

MagBoltz

Application of GEM

Shoji Uno (KEK-DTP)

Neutron detector X-ray detector

Soft X ray Hard X ray Light

Application to Neutron Detector

Normal GEM

B10 coated GEMs

Readout board

Cathode plateWith B10

Ar-CO2

• Expensive 3He Gas is not necessary. – No pressure vessel

• Free readout pattern

• High resolution– Position and Time

• Insensitive against g-ray

• Capability against high counting rate

Chamber structure

1 mm ( 0.5mm )

Readout strip

2 mm

1 mm

EI = 4.0kV/cm

GEM 2

ET = 2.2 kV/cm

ED = 1.5 kV/cm

Ar/CO2 = 70:30

GEM 1

1 mm

2 mm

B GEM 1

B GEM 2

ET = 1.5 kV/cm

ET = 1.5 kV/cm

Al - 10B cathode

150V (75V)

150V240V

240V150V400V

440V

370V

800V

X(120) +Y (120) strips0.8mm pitch

Thickness of Boron-10 : 4.4m2.0m + 0.6m ×48 mm

Ethernet

GEMChamber

• I/F– One HV cable– Three LV cables– One Ethernet cable

• Electronics– 8 ASIC chips + 1 FPGA

• FE2009 ASIC : KEK-DTP• Data transfer and Control through

Ethernet– SiTCP by T. Uchida （ KE

K ）– Using Note-PC

Present Detector System

Low Voltage

Electronics

Compact and Portable System T.Uchida et. al., "Prototype of a Compact Imaging System for GEMdetectors," was published on IEEE TNS 55(2008)2698.

(Å)

11

Data samples

(Å)

L = 18789 mm ~ 18.8 m

L: distance from the source to the detector

The beam profile and its TOF distribution

An image of a cadmium slit and its TOF distribution

L = 18789 mm

27 mm

60 mm

The thickness of the slit ~0.5 mm

This image is produced with a wavelength cut.

Events from 1.5 Å to 8 Å are selected

Our system can obtain a 2D image and its TOF at the same time.

Cd cutoff

Energy Selective Neutron Radiography

Bragg Edge region (Thermal and cold)

Resonance absorption region 　 (E>1eV)

Resonance absorption imaging By T. Kai (JAEA) et al. at BL10 in J-PARC

One more demonstration

EURO coin

TEST Sample

gold coin

Ratio of ToF spectrums with/without sample

Imaging data with around 450sec ToF