GEM Detector
Shoji Uno
KEK
Wire Chamber
• Detector for
charged tracks
• Popular detector in
the particle physics,
like a Belle-CDC
• Simple structure
using thin wires
2
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、
Anode wire
electric avalanche)
• Gas gain up to ~105 can be obtained
easily.
Electron
3
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)
Double side flexible printed circuit board
Electric field
Electrical field
electron
Amplification
GEM foil
3μm Cu
50μm Kapton
3μm Cu
electron
s
Hole diameter 70mm
Hole pitch
140mm
Thickness
50mm
Cu thickness
5mm
Developed by F.Sauli (CERN) in 1997.
NIMA 386(1997)531
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
PCB
Test Chamber
55Fe
(5.9 keV X-ray)
10 mm
1mm
DRIFT
□15mm×15mm
GEM1
GEM2
GEM3
PCB
～2 mm
TRANSFER 1
～2 mm
TRANSFER 2
～2 mm
INDUCTION
GAS
Ar-CH4(90/10) (P-10)
Ar-CO2(70/30)
36＝6×6
2200pF
2200pF
Pulse shape
200ns
Signal from GEM foil
130mV
Signal from Readout pad
P10
Ar-CO2
Number of events
Effective gas gain and resolution
55Fe
Ar-CH4(90/10)
DVGEM=325V
Edrift = 0.5kV/cm
Etransfer = 1.6kV/cm
Einduction= 3.3kV/cm
Pedestal=104.6
ADC counts
Sigma/Mean
= 8.8%
Gas gain vs various parameters
P10
Ar-CO2
P10
Ar-CO2
EI
ED
Ar-CO2
P10
Ar-CO2
ET
EI
55Fe
(5.9 keV X-ray)
ED Ｄｒｉｆｔ region
Collection Efficiency
Electric field dependence in drift region
1.2
1
0.8
0.6
ΔVGEM=360V
ET=1.6kV/cm
EI=3.6kV/cm
0.4
0.2
0
0
0.5
1
1.5
2
2.5
Electric field
In case of weak field
ED=500V/cm
3
3.5
電場 (kV/cm)
(kV/cm)
In case of strong field
ED=3000V/cm
Ionization occurs in drift region
ΔＶＧＥＭ＝３２０Ｖ
ΔＶＧＥＭ＝３２０Ｖ
Electrons enter into GEM holes.
EI=1000V/cm
EI=1000V/cm
Collection Efficiency
Charge
distribution
ADC
σ＝359.7±0.4 μm
ΔVgem＝３３０V
SUMADC
Ed= 0.5 kV/cm
P10
Et=1.65 kV/cm
Ei= 3.3 kV/cm
ADC counts
One event
-1
0
1
ｍｍ
dX (each
strip – C.O.G)
ｄX（各strip－C.O.G)
0
Channel
63
Normalized ADC counts
σ＝181.2±0.3 μm
ΔVgem＝３７０V
Ar-CO2
(70/30)
-1
Ed= 0.5 kV/cm
Et=2.59kV/cm
Ei=5.18 kV/cm
0
1
ｄX（各strip－C.O.G)
dX (each
strip – C.O.G)
ｍｍ
Charge spread
0.546mm/√cm
0.4
P10
0.35
MagBoltz
2
σ (mm )
0.3
0.258mm /√cm
0.25
2
P10
Ar-CO2
0.2
Ar-CO2
0.15
0.1
0
1
2
電場（ｋV/cm)
Diffusion is dominant factor.
3
4
Application of GEM
Shoji Uno (KEK-DTP)


Neutron detector
X-ray detector
 Soft X ray
 Hard X ray
 Light
Application to Neutron Detector
Cathode plate
With B10
Ar-CO2
• Expensive 3He Gas is not necessary.
– No pressure vessel
B10 coated
GEMs
• Free readout pattern
• High resolution
– Position and Time
Normal GEM
Readout board
• Insensitive against g-ray
• Capability against high counting rate
Chamber structure
Ar/CO2 = 70:30
8 mm
Al - 10B cathode
ED = 1.5 kV/cm
1 mm ( 0.5mm )
ET = 1.5 kV/cm
1 mm
ET = 1.5 kV/cm
1 mm
ET = 2.2 kV/cm
2 mm
B GEM 1
B GEM 2
GEM 1
Thickness of Boron-10 : 4.4mm
2.0mm + 0.6mm ×4
150V (75V)
240V
150V
240V
150V
400V
440V
370V
GEM 2
EI = 4.0kV/cm
2 mm
Readout strip
800V
X(120) +Y (120) strips
0.8mm pitch
•
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（KEK）
– Using Note-PC
Present Detector System
Ethernet
Electronics
•
•
•
Low Voltage
Recorded Rate (MHz)
14
12
10
GEM
Chamber
Compact and Portable System
T.Uchida et. al., "Prototype of a Compact
Imaging System for GEM
detectors," was published on IEEE TNS 55(2008)2698.
8
6
4
2
0
0
10
Input Rate (MHz)
Data samples
The beam profile and its TOF distribution
L = 18789 mm ~ 18.8 m
L: distance from the source to the detector
An image of a cadmium slit and its TOF distribution
(Å
)
L = 18789 mm
27 mm
Events from 1.5 Å to 8 Å
are selected
60 mm
Cd cutoff
The thickness of the slit ~0.5 mm
This image is produced
with a wavelength cut.
(Å)
Our system can obtain a 2D image and its TOF at the same time.
11
Energy Selective Neutron Radiography
Resonance absorption
region (E>1eV)
Bragg Edge
region
(Thermal and cold)
Resonance absorption imaging
By T. Kai (JAEA) et al.
at BL10 in J-PARC
One more demonstration
TEST Sample
Ratio of ToF spectrums with/without sample
EURO coin
gold coin
Imaging data with around 450msec ToF