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Coimbra Portugal
Gaseous detectors and applications I
Gaseous detectors I 4th School of High-energy Physics, 26/04/2014 P. Fonte
• Applications of gaseous particle detectors • High Energy and Nuclear Physics • Medical Instrumentation, space, etc.
• The physical detection principles • Interaction of high-energy radiation with gases • Transport and amplification of charges
• Technology • Common requirements/problems • Wire-based devices • Planar devices • Micropattern devices • Miscellaneous
• Some current detector physics research topics • Conclusion
Summary
Gaseous detectors I 4th School of High-energy Physics, 26/04/2014 P. Fonte
Applications High Energy Physics
@ CERN/LHC
MWPC
TPC
RPC
Gaseous detectors I 4th School of High-energy Physics, 26/04/2014 P. Fonte
Applications High Energy Physics
The OPERA neutrino oscillation experiment at the underground “Laboratorio Nacional de Gran Sasso” (LNGS), Italy, which takes a neutrino beam from CERN.
RPC (180m2)
RPC (1380m2)
RPC (1380m2)
Gaseous detectors I 4th School of High-energy Physics, 26/04/2014 P. Fonte
Applications Nuclear Physics
Collaboration (GSI, Darmstadt, Germany) High Acceptance Di-Electron Spectrometer
MDC MDC
MDC MDC MWPC
photodetector
MWPC (SQS mode) RPC
Not gaseous!
Gaseous detectors I 4th School of High-energy Physics, 26/04/2014 P. Fonte
Applications Nuclear Physics
Super heavy-nuclei synthesis experiment, JINR, Dubna
PPC time-of-flight detectors
Gaseous detectors I 4th School of High-energy Physics, 26/04/2014 P. Fonte
Applications Ion microscopy
Indestructible detection medium (no rad. damage) Better resolution than Si for the heavier ions
[M.D
oeb
eli,
Pilt
vice
20
10
]
@1MeV 2D STIM
PIN diode Gas ionization chamber
[A.C
.Mar
qu
es e
t al
, IC
NM
TA 2
01
2]
56×56 m2 grid
224×224 m2 scales on a
butterfly wing
Gaseous detectors I 4th School of High-energy Physics, 26/04/2014 P. Fonte
Applications Low-level medium-energy (100’s keV) gamma detection
High-pressure Xe ionization chambers Large SEALED sensitive volume Excellent (few %) energy resolution Commercially available
[H.S
. Kim
, 19
98
]
Gaseous detectors I 4th School of High-energy Physics, 26/04/2014 P. Fonte
Applications Astronomy
X-ray telescope (Beppo-Sax satelite)
Gaseous Scintillation Proportional Counter (GSPC)
X-ray image and spectrum of the Cygnus-X1 galaxy
Gaseous detectors I 4th School of High-energy Physics, 26/04/2014 P. Fonte
Applications Neutrinoless double beta decay (search for)
The NEXT experiment
TPC readout by a Gaseous Scintillation Proportional Counter (GSPC) To be installed at Canfranc, Spain
Gaseous detectors I 4th School of High-energy Physics, 26/04/2014 P. Fonte
Applications Astronomy
X-ray polarimeter on-board HXMT satelite
Gas pixel polarimeter
GEM
The photoelectron’s direction correlates with the X-ray polarization
[E. C
ost
a et
al.,
20
01
]
pixelized readout chip
Gaseous detectors I 4th School of High-energy Physics, 26/04/2014 P. Fonte
Applications Medicine diagnostics
XCT Gas Avalanche Detector for digital radiography (Xcounter AB)
PPC or RPC
Gaseous detectors I 4th School of High-energy Physics, 26/04/2014 P. Fonte
Applications Medicine diagnostics
Ultra low dose whole-body digital radiography
(Biospace EOS)
MICROMEGAS
[P. D
esp
rés
et a
l., 2
00
4]
Gaseous detectors I 4th School of High-energy Physics, 26/04/2014 P. Fonte
Applications Medicine diagnostics
[J.E
.Bat
eman
et
al.,
19
84
]
MWPC inside
0
5000
10000
15000
20000
25000
30000
0 30 60 90 120 150 180 210 240
Axial Field of View (cm)
3D
Tru
es S
en
sit
ivit
y (
kcp
s/m
Ci/cc)
GE Advance - 11 Rings (Lewellen et al)
GE Advance - 11 Rings (this simulation)
GE Advance - 17 Rings (Lewellen et al)
GE Advance - 17 Rings (this simulation)
60 Plates - 5.7 degrees
60 Plates - 15 degrees
60 Plates - 30 degrees
60 Plates - 45 degrees
60 Plates - Full Acceptance
120 Plates - 5.7 degrees
120 Plates - 15 degrees
120 Plates - 30 degrees
120 Plates - 45 degrees
120 Plates - Full Acceptance
G E Ad v an ce (A F O V =15 cm )
Lew e llen e t a l T h is s im u la tion
11 1020 1013
17 1248 1160
T ru es sen s itiv ity
(kcp s /u C i/cc ))R ing
D iffe rence
20-fold higher sensitivity compared with the GE ADVANCE tomograph
RPC inside
[Co
uce
iro
20
07
]
Low cost human Positron Emission Tomography (PET)
(in development)
Gaseous detectors I 4th School of High-energy Physics, 26/04/2014 P. Fonte
Applications Biology
High resolution Positron Emission Tomography (PET) for small animals
MWPC inside
RPC inside
0.47 mm FWHM
(FBP algorithm) 50
100
150
200
-10 -5 -1 1 5 100
10
20
30
40
Distance (mm)
Counts
/100
m
50
100
150
200
-10 -5 -1 1 5 10 0
10
20
30
40
Distance (mm)
1 1 9mm
Almost physics-limited resolution
[Bla
nco
20
06
]
Resolution: 0.9 mm FWHM
Gaseous detectors I 4th School of High-energy Physics, 26/04/2014 P. Fonte
Why gaseous detectors? (despite strong competition from solid state)
Very large areas/volumes are possible Low cost per unit area or readout channel (no light sensor) Very low average specific mass Quite good, sometimes outstanding, position and time accuracy
- Often limited in rate capability - Most types are vulnerable to dangerous sparks - Mostly “homemade”
Gaseous detectors I 4th School of High-energy Physics, 26/04/2014 P. Fonte
Interaction of high-energy radiation with gases Heavy charged particles
Gas
High-energy charged particle
Electromagnetic collisions Electrons ejected with energies following a “Landau distribution” Randomly distributed “ionization clusters” (most <0.1mm diameter) ~few ionization clusters/mm (gas and particle energy dependent) Nr. of electron-ion pairs/cluster follows ~1/N2 distribution
Ionization minimum (=p/mc3)
Gaseous detectors I 4th School of High-energy Physics, 26/04/2014 P. Fonte
Interaction of high-energy radiation with gases Heavy charged particles
Particle identification (PID) by energy loss ( number of clusters/mm) in a gas
[Par
ticl
e D
ata
Bo
ok]
Highly accurate measurement of the
cluster density
requires large volumes of gas
Gaseous detectors I 4th School of High-energy Physics, 26/04/2014 P. Fonte
10-3
10-2
10-1
100
101
102
10-2
10-1
100
101
102
103
104
Photon energy (MeV)
Abso
rbtio
n le
ngth
(m
)
Xe, 1 atm
photoelectric
Compton
pair production
Total
Interaction of high-energy radiation with gases Photons
• Single photoelectric, Compton or pair-production interaction site • Electrons (ionizing or not) are injected into the gas
Gas
Deep UV or low-energy X-ray)
ejected electrons
X- or gamma-ray
Surrounding material (converter plate)
Photocathode
e.g.: CsI
Near UV (down to ~300 nm)
Gaseous detectors I 4th School of High-energy Physics, 26/04/2014 P. Fonte
Interaction of high-energy radiation with gases neutrons
• Nuclear interaction on fissile nucleus with large n cross-section (energy dependent) • Ionizing fission fragments are injected into the gas
Fe converter plate
Gas rich in 3He or 10BF3
ejected ionizing fission
products
10B converter layer
higher n energies
lower n
energies
Neutron interactions in 3He visualized with scintillating GEM + optical readout
Gaseous detectors I 4th School of High-energy Physics, 26/04/2014 P. Fonte
Transport and amplification of charge
basic features
Typical drift electric field ~1kV/cm
Primary electrons drift towards the amplification region with velocity v(E), strongly gas-dependent.
A Townsend avalanche (streamer, spark…) develops in the amplification region. Electrical or optical signals are generated.
Drifting electrons are subject to attachment (to be avoided) and diffusion (detrimental to localization accuracy)
Typical amplification electric field: 10 to 100 kV/cm
Drift (charge collection)
region
Amplification region
v
E
Gas volume
Electrical signal Optical signal
Gaseous detectors I 4th School of High-energy Physics, 26/04/2014 P. Fonte
Common requirements/problems drift region
Drift (charge collection) region ‐No electron attachment ‐Most often high ionization density is desired but for photodetectors it is good to be “particle-blind” ‐For some applications with long, precise, drifts
• Low diffusion • Drift velocity not much dependent on E field
e-
Ionizing
particle
Gaseous detectors I 4th School of High-energy Physics, 26/04/2014 P. Fonte
Common requirements/problems amplification region (gas + electrodes)
Amplification region
Electrical signals Optical signal
Related to charge amplification • Large average gas gain (typical range: 103-108)
• Reduced UV photon emission (to avoid photon feedback) • Resistance to the avalanche streamer transition (larger spark-free gain)
• Favourable avalanche statistics (narrow distribution of gain) Resistance to polymerization “aging“ If optical signal is sought, efficient visible/near UV light emission
For some applications requiring precise drifts: minimization of ion backflow to avoid E-field distortion
photon and ion production
e-
i+
e-
Secondary avalanches
Coupling structure (transfer optimization, spark protection)
Pickup electrode structure (avalanche localization, spark protection)
UV
Gaseous detectors I 4th School of High-energy Physics, 26/04/2014 P. Fonte
Some special configurations Multistep (cascaded)
amplification Ionization chamber
Allows slightly larger total gain
(still space-charge limited)
e-
Drift region
Signal
Very high particle rate (e.g.: beam dosimetry) Highly ionizing particles
(e.g.: alphas, fragments, ions)
Driftless
Reduced efficiency Simplicity
Excellent timing
Amp. region 1
e-
Transfer drift
Collection drift
Amp. region 2
Transfer drift
Amp. region 3
Signal
signal drift
Amp. region
Signal
Each primary charge
sees a different gain
unfavourable gain
statistics: ~1/Q
Gaseous detectors I 4th School of High-energy Physics, 26/04/2014 P. Fonte
Almost all detectors work at atm. pressure for technical convenience
DRIFT: electronegative gases forbidden Noble gases as main mixture components • He: light “filler” gas for particle-blind detectors (e.g.: photodetectors) • Ar, Xe: heavy gases for high primary charge density + a few % of more complex molecules to “quench” the UV light emission hydrocarbons • CH4: light quencher, some UV emission some photon feedback • C4H10: excellent quencher but strongly polymerizes aging • vapours also possible (e.g.: alcool, acetone, trimethylolethane (TME), etc) other • CO2: very light quencher. Doesn’t work in many detector types. However it provides very fast drift and doesn’t polymerize. • CF4: also very light quencher, but very luminous in visible/near UV. DRIFTLESS: electronegative gases allowed • Fluorinated mixtures work very well. Huge, saturated, gain before
discharges appear (e.g. “RPC mixture”: 85% C2H2F4 + 10% SF6 + 5% C4H10)
Choice of gas mixtures (alta cozinha)
Gaseous detectors I 4th School of High-energy Physics, 26/04/2014 P. Fonte
Wire-based devices cylindrical counter
Proportional Geiger Self-quenched streamer (SQS)
Geiger mode: photon-mediated discharge propagation
Self-quenched streamer (SQS) mode streamer “dies” in the strong non-uniform E-field around the wire Drift
Drift
Amplification
[G.D
.Ale
ksee
v et
al.,
19
79
]
Gaseous detectors I 4th School of High-energy Physics, 26/04/2014 P. Fonte
IEEE October 2003, Portland, US Mar Capeans 6
Barrel straw
Wire joint
Twister
Wire
30 mEnd plug
Straws embedded in radiators
and supported by dividers and
endplates; connected across the module by a C-fibre shell
C-fiber shell
Radiator
Straws
Tension plate
Tension plate
Wire-based devices cylindrical counter (proportional mode)
Modern example: the ATLAS (CERN) Transition Radiation Tracker (TRT) made with ~400.000 “straw tubes”
Electrons with
radiator
Electrons without radiator
Electrons with
radiator
Electrons without radiator
Gaseous detectors I 4th School of High-energy Physics, 26/04/2014 P. Fonte
Wire-based devices multi-wire proportional chamber (MWPC)
“sense” HV wires typ. 20m
drift region
drift region
High E field (up to 100kV/cm) amplification region
Cathode wires or strips
Position resolution 0.1mm (by the centroid of the charges induced in the cathodes)
Time resolution ~50ns (variable drift distances)
Difficult mechanics. Any wire rupture compromises the whole chamber.
Potential and field lines Monte-Carlo simulation of electron trajectories
at low pressure
High-accuracy position readout (“cathode strip chamber” - CSC)
The workhorse of modern particle
detectors G.Charpak Nobel laureate 1992
[H. P
ruch
ova
et
al.,
19
79
]
Gaseous detectors I 4th School of High-energy Physics, 26/04/2014 P. Fonte
Wire-based devices Drift Chamber, Time projection chamber (TPC)
A neat recent development: the negative-ion drift chamber • primary electron capture in CS2, drift of CS2
- , e- released in the amp. space and amplified; • dramatically decreases diffusion in the drift volume.
MWPCs for 2D (x,y)
and drift time (z)
measurement
z
y
TPC electron drift
Huge gas volume
Drift chamber
Beam Beam
x E The TPC of the DELPHI
experiment
In many senses the most perfect gaseous detector
(huge, high accuracy, PID)
• Measures trajectories in 3D • Low count rate owing to the huge drift time
Gaseous detectors I 4th School of High-energy Physics, 26/04/2014 P. Fonte
Wire-based devices Multidrift chamber (MDC)
Actual event
Cellular structure of anode and cathode wires •Multiple measurements of the same particle
provide excellent position and angle information in 2D.
• Much higher rate capability than TPC •Extremely demanding construction
Equipotential and field lines
radius=
drift time
Gaseous detectors I 4th School of High-energy Physics, 26/04/2014 P. Fonte
Planar geometry with drift (multistep possible) Top drift electrode (solid or wire mesh)
Upper gap electrode (wire mesh or micromesh)
Lower gap electrode (solid or wire mesh)
Signal pickup electrode (patterned, mesh or solid)
may be used as the lower gap electrode also
Amplification gap
Drift gap
d
Signal gap
[Gio
mat
aris
, 19
96
]
if d> ~1 mm: Parallel-Plate Avalanche Chamber (PPAC) if d< ~1 mm: MicroMEsh GAseous Structure (MICROMEGAS) (to be considered as a “micropattern” detector)
Gaseous detectors I 4th School of High-energy Physics, 26/04/2014 P. Fonte
Planar geometry with drift Gaseous Scintilation Proportional Chamber (GSPC)
Much used for soft X-ray
detection
[CA
N C
on
de,
A. P
olic
arp
o 1
96
7]
• Detector based on the emission of light from optimized mixtures of noble gases
• The statistical characteristics of light emission are more favourable than those of charge multiplication, so, for soft X-rays below about 2 keV, GPSCs energy resolution outperforms any other type of large area detector, either cooled or room temperature.
Schematic of a GPSC:
1. first grid;
2. second grid;
3. gas outlet to purifier
4. entrance window;
5. stainless steel
enclosure.
Gaseous detectors I 4th School of High-energy Physics, 26/04/2014 P. Fonte
Planar geometry - driftless
Amplification gap d~4 mm Upper gap electrode (solid, foil)
Lower gap electrode (solid, foil)
Parallel-Plate Chamber (PPC)
All planar detectors with metallic electrodes are prone to sparking, so…
Only successful application: timing of fission fragments at low pressure
Spark Chamber
Electronics
HV pulse
External detector
None of these configurations is
much used in practice today
Gaseous detectors I 4th School of High-energy Physics, 26/04/2014 P. Fonte
Planar geometry - driftless Resistive Plate Chamber (RPC)
A very successful detector
[San
ton
ico
, 19
81
]
The current is limited by the resistive electrodes: no sparks by construction • Deployed in huge areas (~10000 m2) • Outstanding time resolution (50 ps) – the standard technique today for
large-area time-of-flight measurements on relativistic particles • Main drawbacks: quite limited rate capability
quite insensitive to primary energy deposition
Resistive electrode
Resistive electrode
Gas gap (from 0.2mm to a few mm)
Medium resistivity layer
(e.g. Graphite)
transparent to the induced
signals
High resistivity layer
(e.g. PET)
X pickup strips (at ground potential)
Y pickup strips (at ground potential)
+HV
-HV Resistive electrodes
(glass, bakelite)
Gaseous detectors I 4th School of High-energy Physics, 26/04/2014 P. Fonte
Gas
Substrate
Streamer
Very high E-field point
An
od
e
Micropattern detectors Microstrip Gas Chamber (MSGC)
A very original idea
• Thin anode strips and wider cathode strips deposited by industrial lithographic methods on a glass substrate. A kind of solid MWPC.
• Abandoned because it is extremely prone to sparking, melting the thin strips.
• The surface strongly facilitates the streamer progression for electrostatic reasons.
In the 90’s hundreds of people worked on this detector and its infinite
variations and derivatives
[A.Oed, 1988]
Gaseous detectors I 4th School of High-energy Physics, 26/04/2014 P. Fonte
Micropattern detectors MICROMEGAS (already mentioned)
Gas electron Multiplier (GEM)
•Flexible detector made by chemically drilling small holes in a thin kapton printed circuit board.
•Cascadable
Very fashionable detectors today
Optical detection of alpha tracks (in CF4)
[F.S
auli,
19
97
]
Gaseous detectors I 4th School of High-energy Physics, 26/04/2014 P. Fonte
Micropattern detectors Micro-Hole & Strip Plate (MHSP)
GEM
+
MSGC
• Somewhat higher gain • Reduced ion backflow
[J.F
.C.V
elo
so, 2
00
0]
Gaseous detectors I 4th School of High-energy Physics, 26/04/2014 P. Fonte
Micropattern detectors Compteur a trou (CAT) MicroDot
Laid in silicon
[S.F
. Bia
gi e
t al
. 19
95
]
[M. L
emo
nn
ier,
19
95
]
Gaseous detectors I 4th School of High-energy Physics, 26/04/2014 P. Fonte
Other micropattern detectors (likely not an exhaustive list)
[F. Angelini et al.,1993]
[R. Bellazzini et al, 1998]
[R. Bellazzini et al, 1999]
[A.H. Walenta et al., 1998]
[C. Labbé, 1998]
[B. Adeva et al, 1999]
Micro Gap (MGC) Micro WELL Micro Groove Micro CAT Micro Slit (MSGD) Micro Wire (µWD)
[H. Sakurai et al, 1996] Capillary Plate Gaseous Detector (CPGD)
Gaseous detectors I 4th School of High-energy Physics, 26/04/2014 P. Fonte
Main characteristics of the different amplification structures WIRE (cylindrical)
Somewhat resilient to sparking owing to the very non-homogeneous E field (SQS mode) Hugely applied - Reduced count rate capability (ion pile-up at the wire reduces E field) - Inherently anisotropic: the position resolution is better along the wire - Timing not so good owing to variable drift distances for each primary charge (~50ns)
PLANAR - metallic Simple mechanics Reasonable rate capability - Prone to sparking, as the streamer develops well in the uniform E-field
PLANAR – resistive (RPC) Very high gain (by construction, only small discharges allowed, not sparks) Simple mechanics Outstanding timing (~50 ps) - Limited rate capability
MICROPATTERN High rate capability Very good position resolution even in digital readout mode (hit-counting) Good timing (~5ns) Industrial production methods, derived from electronics industry - Small gain (mostly limited by imperfections on tiny structures, leading to sparking)
Gaseous detectors I 4th School of High-energy Physics, 26/04/2014 P. Fonte
Some open physics issues in gaseous detectors The limits of charge amplification
[Iva
nio
uch
enko
v 1
99
9]
Rate-induced
breakdown
Ma
xim
um
ach
ieva
ble
ga
in
Rate density (counts/s/mm2)
Forbidden
region
(by sparks)
Gain-induced
breakdown
Superimposed limits of many detector types
Gaseous detectors I 4th School of High-energy Physics, 26/04/2014 P. Fonte
Some open physics issues in gaseous detectors gain-induced breakdown
Meek and Raether’s “streamer”/”Kanalaufbau” mechanism
Gain
Typical “precursor” structure can be easily
reproduced by numerical calculations
[Fo
nte
19
94
]
Higher space-
charge generated
E-field allows the
cathode streamer
but a secondary
process is
needed to feed
the high-gain
region Gas self-photoionization
This process exists in all tested gas mixtures (and we tried a lot…) Is there an universal process for gas self-photoionization close to the Townsend avalanche conditions?
Gaseous detectors I 4th School of High-energy Physics, 26/04/2014 P. Fonte
Hydrodynamic approach to streamer calculation
Charge transport
2( , )( ) ( )
e e e e
drift pile up
transportcreation
ee e e e e e
otherdiffusionW n n Wsources multiplication
attachment
n r tS W n W n D n
t
electrons
good reference: [DAV73]
( , ) charge density inspaceand time
( ) velocity of charges
( , ) electricfield:applied+spacecharge
=first Townsend coefficient
=diffusion coefficient
n r t
W E
E r t
D
( , )
( , )
ie e
ie e
n r tS W n
t
n r tW n
t
Ions, assuming
stationary ions
Space-charge + applied field
2
0
( )i e i
eV n n n
Boundary conditions
,initialdensities: ( ,0)
behaviour of chargesat theelectrodes
Electrostatic B.C.
e in r
Slight drawback: no avalanche statistics
Gaseous detectors I 4th School of High-energy Physics, 26/04/2014 P. Fonte
Numerical approach: finite elements
Used the commercial program COMSOL Multiphysics
Solves a coupled set of a basic
differential equation,
with arbitrary coefficients (any function of
any variable) in a mesh (finite elements).
Covers most cases needed for applied
physics.
[COMSOL]
Gaseous detectors I 4th School of High-energy Physics, 26/04/2014 P. Fonte
GEM lateral (ring) avalanche
hole: 60 µm
gap: 100 µm
N0=100 e-
V=1250V
Gaseous detectors I 4th School of High-energy Physics, 26/04/2014 P. Fonte
GEM lateral (ring) avalanche
hole: 60 µm
gap: 100 µm
N0=100 e-
V=1250V
Notice the precursor!
Gaseous detectors I 4th School of High-energy Physics, 26/04/2014 P. Fonte
Cathodeless CAT
Will the streamer be able to
grow out of the hole?
Gaseous detectors I 4th School of High-energy Physics, 26/04/2014 P. Fonte
Cathodeless CAT
Not completely successful, but
it sparks at a rather large
charge.
Maybe such geometries can
be optimized for SQS mode.
Gaseous detectors I 4th School of High-energy Physics, 26/04/2014 P. Fonte
Some open physics issues in gaseous detectors rate-induced breakdown
Reason unknown… Observations
5 A
1 s
PPAC - high rate, low gain – single sparks
200 nA
500 ms
20 A
1 s
[IVA98]
500 nA
500 ms
500 nA
500 ms
(Cu cathode)
(Si cathode)
afterpulses after irradiation PPAC - medium rate - higher gain
continuous sparking regime
+ memory effect (cannot reach same gain for hours)
[Iva
nio
uch
enko
v 1
99
8]
[Iac
ob
aeu
s 2
00
2]
Gaseous detectors I 4th School of High-energy Physics, 26/04/2014 P. Fonte
Conclusion
• Despite a venerable history, gaseous particle detectors are very versatile, offer unique capabilities and have still today many applications
• The innovations have been constant over the last decades. Recent examples include micropattern detectors, the negative-ion drift chamber and time-of-flight measurement capability on minimum-ionizing particles.
• Some aspects of the avalanche to streamer transition remain to be clarified, as well as the origin of high-rate breakdown.