Download K. Nikolopoulos (Univ. of Athens) – Recent Developments in Light

Recent Developments
In Light Detection
Konstantinos Nikolopoulos
University of Athens
Experimental Methods I, 4th July 2005
Why detect light?
Usage of Light detection in High Energy Physics*
*short list of indicative examples
Light is used in many aspects of HEP experiments
• Calorimetry
• Tracking
–
•
Particle Identification
–
•
Scintillating Fiber Trackers
Cherenkov
Medical Imaging
–
–
PET
SPECT
Light Detectors are used in enormous numbers at HEP
• Super – Kamiokande
–
•
Pierre Auger Prototype Fluorescence telescope
camera (440 photomultiplier tubes)
Cherenkov Counters  13.000 PMTs
Pierre Auger Observatory
–
Fluoresence Detectors  10.560 PMTs
Light detection is crucial for every kind of high
energy physics experiment.
Aim of this presentation is summarize current
trends in light detection
Super – Kamiokande 20- inch PMT tube (Venetian Blind)
K. Nikolopoulos (Univ. of Athens) – Recent Developments in Light Detection – July 4th 2005
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Physics of Light Detection
•
Photoelectric Effect
– When a photon impinges on the surface of any material, it can liberate an
electron provided that the photon energy is higher than the photoelectric
workfunction Φ. The liberated electron carries kinetic energy W=hν-Φ, which can
be sufficient to bring the electron not only from the surface, but also from the
volume of the material to the free space.
– Semiconductors have a very small workfunction Φ.
•
Electron lift from Valence Band to Conduction Band in a
Semiconductor
– When an photon impinges on a semiconductor, then an electron from the
valance band can be lifted to the conduction band. When the electron cannot
recombine with the hole, due to the electric field of a silicon photodiode, it can be
collected and the signal amplified.
The second process is far more efficient in light detection both in
terms of detection efficiency and wavelength sensitivity, because it
needs less energy O(1 eV) than the photoelectric effect one O(10
eV).
K. Nikolopoulos (Univ. of Athens) – Recent Developments in Light Detection – July 4th 2005
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Main Characteristics of Light Detectors
•
Quantum Efficiency
–
•
Gain
–
•
Dark current
Nuclear counter effect (=The extra amount of charge produced in the photodiode by a
charged particle directly hitting it, on the top of the charge produced by th scintillation light).
Experimental Conditions
–
•
Capability of providing time and position information of the incoming photon
Noise
–
–
•
Minimum # of photons required for output signal
High – Voltage Supply
Timing and Positioning
–
•
Multiplication of the initial signal
Sensitivity
–
•
•
The efficiency in single photon detection
B-field, Temperature, Radiation Levels, Particle Rate, e.t.c.
Complexity of construction
–
–
Physical Shapes of Detectors
Price
K. Nikolopoulos (Univ. of Athens) – Recent Developments in Light Detection – July 4th 2005
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Types of Light Detectors
• Vacuum Devices
• Solid – State Devices
• Hybrid Devices
• Gaseous Detectors
K. Nikolopoulos (Univ. of Athens) – Recent Developments in Light Detection – July 4th 2005
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Vacuum Devices
The first photoelectric tube was produced by Elster and Geiter in 1913.
The first photomultiplier tube was invented by the RCA laboratories in 1936.
Features:
• Low noise amplification
–
•
High Gain O(106)
–
–
•
Output read by standard electronics  No need for amplification  No additional noise
Gain = f(# dynodes)
Good Energy resolution
–
•
Due to the dynode – chain amplification scheme. Only noise contribution is the stochastic nature of the
secondary e- emission
Calorimeters with scintillating crystals
Single photon detection
K. Nikolopoulos (Univ. of Athens) – Recent Developments in Light Detection – July 4th 2005
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Vacuum Devices II
Many dynode chain design exists, with different properties!
• Linear Focused Type
– Fast Response
– Linearity
– Large Output Current
Linear Focused
• Box - and - Grid Type
– Consist of a series of quarter cylindrical dynodes.
– Electron collection efficiency
– Uniformity
Box – and – grid
• Circular Cage Type
– Compactness
– Fast Response
– High gain (with relatively low High—Voltage)
• Venetian Blind Type
Circular Cage
– Large dynode area (large photocathode area)
– Uniformity
– Large Output current
Venetian Blind
K. Nikolopoulos (Univ. of Athens) – Recent Developments in Light Detection – July 4th 2005
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Vacuum Devices III
Drawbacks:
• Q.E. typically constrained to ≈25%
–
–
–
Reflection of photons by the glass of the window
Passage of photons through the photocathode without interaction
The produced photoelectrons may stop inside the cathode material
• Shape dictated by technical restrictions in the fabrication of the
vacuum container
– Hand work involved  Expensive to construct
• Very sensitive to B – field
– Defocusing of the e-
K. Nikolopoulos (Univ. of Athens) – Recent Developments in Light Detection – July 4th 2005
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Further Innovations in Vacuum Devices
• Sensitivity to B—field
– Dynodes from meshes with small distance O(1mm) and high field between them.
• Information on the position of the incoming photons
– Metal – channel devices. The single dynode chain is replaced by many chains in
parallel and there is a segmented anode.
• New photocathode and window materials
Metal – Channel Device
Mesh Dynodes
K. Nikolopoulos (Univ. of Athens) – Recent Developments in Light Detection – July 4th 2005
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Solid – State Devices
Photosensors made of semiconductor material gained much
attention in recent years.
• High Q.E.
– Main negative contribution is the reflection at the surface
• Insensitivity to magnetic fields
– Theoretical Limit ≈ 15 T
• Produced in standard fully – automated processes
– Inexpensive
• Fairly easy to be tailored for individual needs
– In short time
• Low mass
• Small space consumption
– Thickness < 1/2 mm
They open new areas of application!
K. Nikolopoulos (Univ. of Athens) – Recent Developments in Light Detection – July 4th 2005
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PIN Photodiode
•
•
•
The PIN photodiode is a semiconductor device, typically
fabricated using doped silicon. In a photodiode, absorption
of an incoming photon produces a single electron-hole pair.
A small electric field within the photodiode causes these
charge carriers to migrate in opposite directions towards
external electrodes. This results in a measurable current or
voltage, which has a linear relationship to the incident light
flux.
The silicon PIN diode is a very successful device. All major
experiments in high-energy physics used it in big numbers
in the last 2 decades. The operation is simple and reliable
but since it has no gain it needs a charge-sensitive amplifier
that adds to the cost and creates noise in the readout
system. Single photon detection with silicon photodiodes is
therefore not possible and the very good timing properties
(1–2 ns) are destroyed by the signal rise time of the
amplifier which is 10 ns or more.
Arrays of photodiodes are easy to produce and are
commercially available
K. Nikolopoulos (Univ. of Athens) – Recent Developments in Light Detection – July 4th 2005
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Avalanche Photodiodes
• Avalanche Photodiodes provide gain due to the
high internal field at the junction of positively and
negatively doped silicon.
– The incoming photon produces an e-h pair.
– The electron gain enough energy due to the high internal
field to produce secondary electrons by impact ionization
– An electron avalanche is created
• Gain is 50 – 200.
– Higher gains (up to 104) can achieved
•
•
•
•
Schematic Diagram of an APD
Q.E. is of O(80%).
Large Dynamic range
Excellent energy resolution
Position information
– Only with dedicated setup  position resolution
O(0.3mm)
• Drawback: Very stable environment of operation
needed for gains over a few hundreds.
– 1% gain variation  δT= 0.1 K or δV/V=10-4
Hamamatsu S8148
K. Nikolopoulos (Univ. of Athens) – Recent Developments in Light Detection – July 4th 2005
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Avalanche Photodiodes in Geiger Mode
• In this case the APD is operated at a bias voltage higher than the
breakdown voltage.
• Any photon or thermally liberated electron starts an avalanche.
• The avalanche persists until the voltage is lowered actively or when
the voltage drops on a properly chosen serial resistance.
• The output signal is proportional to the over – voltage and the
capacitance of the APD.
• Drawback: There is a long dead time O(1 ms) after each
breakdown.
K. Nikolopoulos (Univ. of Athens) – Recent Developments in Light Detection – July 4th 2005
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Silicon Photomultipliers (SiPM)
• The SiPM is a novel type of APD.
• It is a multipixel silicon photodiode with a number of micropixels of
size O(20 μm) joined together on common substrate and working on
common load.
• The operational bias voltage is ≈15% higher than the breakdown
voltage.
– The pixels are electrically decoupled from each other.
– Each SiPM pixel operates in Geiger mode
• Each SiPM pixel operates as a binary device
• The SiPM as a whole is an analogue detector.
The SiPM intend to solve the problem of long dead time in the APDs
functioning in Geiger mode.
K. Nikolopoulos (Univ. of Athens) – Recent Developments in Light Detection – July 4th 2005
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Silicon Photomultipliers II
•
Detection efficiency.
–
–
•
Gain O(106)
–
•
•
<#photons/pixel> << 1 (signal saturation)
Electronics noise is negligibly small
–
–
•
Independent of primary carrier number.
Excellent energy resolution.
Dynamic range O(10^3/mm^2).
–
•
Q.E. is of O(80%).
εgeometrical=Ssensitive/Stotal, is of O(25%).
High gain
Electronic noise contribution < 0.1 e-
Single Photon Detection Efficiency of a SiPM, a APD
and a classical PMT
Main noise contribution is the dark rate.
–
–
–
–
Originates from carriers created thermally in sensitive volume or due to effects of high
electric fields.
O(1 MHz/mm2) @ room temperature
≈1kHz/mm2 @ 100 K
However, dark rate limits SiPM performance only in detection of very small light intensities
O(1 ph.e.).
K. Nikolopoulos (Univ. of Athens) – Recent Developments in Light Detection – July 4th 2005
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Silicon Photomultipliers (SiPM) III
• Insensitive to B – fields
• Excellent time resolution (≈100 ns) for single
photo – electron detection
– Time Resolution obeys the Poissonian law of
1/√Npixelsfired
• Fast rise time ≈1ns
– The discharge is contained within a limited region in
the depletion zone (due to the voltage distribution)
small duration
• Does not suffer from nuclear counter effects
• Stable operation in room temperature
– Low gain variation with temperature
– ΔΤ = 2.5 Κ for 1% gain variation.
• Does not exhibit any serious radiation
damage
– Perhaps Neutrons are an exception to this rule
Response of SiPM to light of very low
intensity. The number of photons can
be counted for each event.
K. Nikolopoulos (Univ. of Athens) – Recent Developments in Light Detection – July 4th 2005
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Hybrid Detectors (HPD)
• These detectors combine the advantages of
the vacuum devices and the solid – state
devices
– Pixel – HPD
– Pad – HPD
• The vacuum container and the photocathode
are the same as in the classical PMT.
• The photo – electrons are accelerated in a
high electric field and are focused onto an
anode:
Schematic view of the Pixel HPD
– A silicon PIN photodiode, an amplification of 4000 is
achieved with an electric field of 15kV.
– An APD, a gain of more than 105 can be achieved,
allowing usage of simple readout electronic circuit.
Simulated potential
distribution and electron
trajectory
K. Nikolopoulos (Univ. of Athens) – Recent Developments in Light Detection – July 4th 2005
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Hybrid Detectors (HPD) II
• Q.E. is of O(20%) @ 270 – 400 nm
• εgeometrical is of O(80%).
– Using electron optics.
• Position information
– When the anode is segmented.
• The HPDs have a very good energy
resolution, even for light of very low
intensity.
Typical photoelectron spectrum
K. Nikolopoulos (Univ. of Athens) – Recent Developments in Light Detection – July 4th 2005
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Visible Light Photon Counters (VLPC)
VLPCs are solid state photo – detectors, originally invented at Rockwell International
and presently developed and manufactured by Boeing.
• The operation principle of VLPCs is the effect of impurity band.
–
–
•
•
The standard 1.12 eV gap of Si is used to absorb photons
The small gap with the impurity band is used for creating an electron – D+ avalanche
multiplication.
–
–
•
Occurs when a semiconductor is heavily doped with shallow donors or acceptors.
The impurity atoms are close together  electrical transport occuring by charge hopping from impurity
site to impurity site!
Small gap O(0.05eV)  Relatively low field is required for avalanche the required field for producing an
avalanche is low.
Localized and self– limiting avalanche(due to local field collapse, D+ have low mobility)
The drift region can been seen as an internal resistor in series with an ideal VLPC
Schematic Layout of a VLPC
Electric Field profile in a VLPC
K. Nikolopoulos (Univ. of Athens) – Recent Developments in Light Detection – July 4th 2005
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Visible Light Photon Counters II
•
•
•
•
•
High Q.E. (80%).
High gain O(5* 10^4).
Low gain dispersion.
Operational in a high background radiation enviroment.
Drawback: Cryogenic temperatures needed!
– In order to freeze out the intrinsic carriers!
VLPC Single Photoelectron
counting capabilities
K. Nikolopoulos (Univ. of Athens) – Recent Developments in Light Detection – July 4th 2005
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Gaseous Detectors
• These detectors have been developed for cases that large areas are
needed to be covered.
• Their functionality principle relies on photo – conversion and
subsequent multiplication in a gas avalanche.
• The photo--conversion can be in the gas itself or in a CsI
photocathode, which can be made in large areas.
• Readout: MWPC e.t.c.
K. Nikolopoulos (Univ. of Athens) – Recent Developments in Light Detection – July 4th 2005
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Gaseous Detectors II
• Main problem: Ion and photon feedback
– Ion Feedback, ionization of the residual gas (Vacuum)
or the gas used (gaseous detectors) in the detector.
Collision of the gas molecules with electrons can cause
the ionization of the gas then a pulse can be created
– Positive ions striking the front dynodes or the
photocathode may produce many secondary electrons
 large noise pulse
– This new pulse usually follows a true photo –electric
pulse  after pulsing
• Solved to some extent by “the gas electron
multiplier (GEM) foil” technique
Field Distribution in the Gas –
Electron Multiplier foil
K. Nikolopoulos (Univ. of Athens) – Recent Developments in Light Detection – July 4th 2005
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The ATLAS Tile Calorimeter
• A Torodial LHC ApparatuS is general purpose
detector to study proton – proton collisions @
√s=14 TeV (some Heavy – Ions Program is
foreseen as well)
• ATLAS is mostly known for its Muon System,
however as a general purpose apparatus, ATLAS
should be able to perform accurate calorimetry as
well.
• The ATLAS calorimetry system is quite
complicated, incorporating different approaches
–
–
–
–
The ATLAS detector
Liquid Argon Sampling Electromagnetic Calorimeter |η|<3.2
Liquid Argon Hadronic Calorimeter 1.5<|η|<3.2
Tile Hadronic Calorimeter |η|<1.7
Forward Calorimeter 3.2<|n|<4.9 (Liquid Argon)
ATLAS Tile Calorimeter Schematic Layout
K. Nikolopoulos (Univ. of Athens) – Recent Developments in Light Detection – July 4th 2005
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The ATLAS Tile Calorimeter II
•
Tile Calorimeter
–
–
–
–
•
Active medium: Tiles of polysterene (emission
maximum ≈100 nm)
Absorber :Steel
Wavelength Shifter Fibers (≈100nm  ≈400nm)
Photo – Multiplier Tubes (10.500) (max sensitivity
≈420nm)
PMT characteristics
–
–
–
–
–
–
–
–
–
–
–
Min/Max wavelength = 300nm/650nm
Max sensitivity @ 420nm
Window : Borosilicate
Photocathode : Bialkali
Gain = 3 105
Dark Current = 2 nA
Rise Time = 1.5 ns
Transit Time = 7 ns
Transit Time Spread = 0.26 ns
Number of dynodes = 8
Operation Voltage = 800 Volt
Tile Calorimeter: Operation Principle
ATLAS polysterene tiles
K. Nikolopoulos (Univ. of Athens) – Recent Developments in Light Detection – July 4th 2005
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The KLOE Electromagnetic Calorimeter
• The main aim of KLOE is to do high precision CP – Violation studies in K0
decays a the Frascati Φ – Factory DAFNE.
• The Electromagnetic Calorimeter
– Sampling calorimeter: Scintillating Fibers are glued inside thin grooved lead layers.
Volume ratio of the composite Pb:scint:glue of 42:48:10 and X0 =1.5 cm.
– Total depth is 23 cm (15 X0) . Containment: 98% of 500 MeV e/m showers (Maximum
shower energy at KLOE).
• Scintillating fibers
– Excellent time resolution for long detectors.
– Relatively long attenuation lenght
– Total fibers lenght is 15000 Km!
• PMTs with Mesh dynodes are used
– E/M Calorimeter inside B-field.
– B- filed strength ≈0.1-0.2 T at the readout.
– The total number of PMTs is 4880.
π0 mass reconstruction using KLOE’s
calorimeter
KLOE Electromagnetic Calorimeter
K. Nikolopoulos (Univ. of Athens) – Recent Developments in Light Detection – July 4th 2005
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The CMS Electromagnetic Calorimeter
•
•
CMS is a general purpose detector for the
Large Hadron Collider
CMS Electromagnetic Calorimeter
–
–
–
Homogenous calorimeter
75.000 PbW04 scintillating crystals used.
Calorimeter dimensions:
The PbW04 scintillating crystals used by
CMS ECal
Longitudinal 25 X0 = 22.2 cm
–
–
–
•
Transverse 1 RM = 2.2 cm
Operation in high B-field  4T
Very High radiation leves
One APD mounted on each side of the crystal depth
of interaction.(Sufficient pulse height from the APDs)
Many sources to be kept under control:
–
–
–
–
–
–
The CMS apparatus
Longitudinal uniformity of light collection
Strong light yield variation with temperature (-2.3%/0C)
APD gain variation with applied tension (-3%/Volt) and
termperature (-2.3%/0C)
Light collection uniformity
light transmission due to radiation damage
Leakage front and rear
Energy Resolution measured with 180 GeV
electrons in 3x3 crystal matrix with 2
APDs/crystal readout
Schematic layout of the
CMS ECAL
K. Nikolopoulos (Univ. of Athens) – Recent Developments in Light Detection – July 4th 2005
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LHCb Ring Imaging Cherenkov
• LHCb is a single arm forward spectrometer designed to perform
various B – physics measurements in the LHC.
• 2 Ring Imaging Cherenkovs
– RICH 1  Aerogel n =1.03 ( 2 – 10 GeV)
C4F10 n =1.0014 (10 – 60 GeV)
– RICH 2  CF4
n =1.0005 (16 – 100 GeV)
– HPDs  61 pixel/HPD
– Magnetic Field, High Radiation Dose
Typical Event from RICH1
Schematic Layout of RICH1
LCHb Schematic Layout
Cherenkov rings produced by 120 GeV π-,
radiator C4F10 .The circle is guide to the eye.
K. Nikolopoulos (Univ. of Athens) – Recent Developments in Light Detection – July 4th 2005
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The D0 SciFi Tracker
• D0 is a general purpose apparatus to study
√s=2 TeV proton – antiproton collisions at
Tevatron.
• Central Scintillating Fiber Tracker
– Consists of 74.000 multi – clad scintillating fibers
– refraction index 1.591.491.42 for improvement of
light trapping
Schematic view of the D0 apparatus
• VLPCs
–
–
–
–
–
–
Q.E. 70%,
Gain 20.000
Rate capability > 10 MHz
Noise Rate <0.1 %
Impurity band 0.05 below the conduction band
Operation at 9K
VLPC wafer
K. Nikolopoulos (Univ. of Athens) – Recent Developments in Light Detection – July 4th 2005
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The GlueX Barrel Electromagnetic Calorimeter
• The goal of the GlueX experiment at Jefferson Laboratory is to
search for gluonic excitations manifested in exotic hybrid vector
mesons with masses up to 2.5 GeV, using linearly polarized photons
of 8 – 10 GeV energy.
• Electromagnetic Barrel Calorimeter
– Sampling calorimeter
– Scintillating fiber
Layout of the GlueX apparatus
K. Nikolopoulos (Univ. of Athens) – Recent Developments in Light Detection – July 4th 2005
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Conclusions
PMT
APD
HPD
SiPM
Blue
20%
50%
20%
12%
Green –yellow
A few %
60 – 70%
A few %
15%
Red
<1%
80%
<1%
15%
Gain
106-107
100 - 200
103
106
High – Voltage
1-2 kV
100 – 500 V
20 kV
25 V
Operation in B-field
problematic
O.K.
O.K.
O.K.
Threshold Sensitivity
S/N>>1
1 ph.e.
≈10 ph.e.
1 ph.e.
1 ph.e.
Timing / 10 ph.e.
≈100 ps
A few ns
≈100 ps
30 ps
Dynamic Range
≈106
large
large
≈103/mm2
Complexity
High
(vacuum,HV)
Medium
(low noise electronics)
Very High
(hybrid technology,
very HV)
Relatively low
γ- Detection Efficiency
K. Nikolopoulos (Univ. of Athens) – Recent Developments in Light Detection – July 4th 2005
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Conclusions (continued)
As concluding remarks we would like to focus on the following:
• Light detection is crucial for every kind of High Energy Physics
experiment.
– One should also note that we didn’t mention at all a very closely related topic,
that of light detection for medical purposes (PET e.t.c.).
• The progress in the field of light detection is enormous. Today, the
market offers light detectors for almost every need and funding.
• Semiconductor devices are a very promising development in the
field. It is expected to be further improved.
• Further progress in the field can be expected.
K. Nikolopoulos (Univ. of Athens) – Recent Developments in Light Detection – July 4th 2005
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References
General
•
D. Renker, Photosensors, Nucl. Instr. And Meth. A 527 (2004), p.15
•
Hamamatsu Photonics , http://www.hamamatsu.com/
Vacuum Devices
•
Hamamatsu Photonics, Photomultiplier Tubes (PMTs) – Construction and Operating Characteristics, http://www.hpk.co.jp/
APDs
•
I. Britvitch et al., Avalanche photodiodes now and possible developments, Nucl. Instr. And Meth. A 535 (2004), p.523
SiPM
HPD
E. Albrecht et al., Nucl. Instr. And Meth. A 442 (2000), p.164
L. Somerville, Pixel hybrid photon detectors for the ring imaging Cherenkov, Nucl. Instr. And Meth. A 546 (2005), p.81
A. Braem et al., Nucl. Instr. And Meth. A 504 (2003), p.19
VLPCs
•
M.D. Petroff, et al., Appl. Phys. Lett. 51 (1987) p. 406
A. Bross et al., Nucl. Instr. And Meth. A 477 (2002), p.172
Gaseous
Experiments
•
The ATLAS experiment, http://atlas.web.cern.ch/Atlas/
•
The CMS experiment, http://cmsinfo.cern.ch/Welcome.html/
•
The LHCb experiment, http://lhcb.web.cern.ch/lhcb/
•
The KLOE experiment, http://www.lnf.infn.it/kloe/
•
The D0 experiment, http://www-d0.fnal.gov/
•
The GlueX experiment, http://www.gluex.org/
•
The Pierre Auger Obervatory, http://www.auger.org/
•
Super-Kamiokande, US Collaboration homepage, http://neutrino.phys.washington.edu/~superk/
K. Nikolopoulos (Univ. of Athens) – Recent Developments in Light Detection – July 4th 2005
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K. Nikolopoulos (Univ. of Athens) – Recent Developments in Light Detection – July 4th 2005
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Positron Emission Tomography
•
•
•
PET produces images of the body by detecting the radiation emitted from radioactive
substances. These substances are injected into the body, and are usually tagged with
a radioactive atom, such as (C-11, F-18, O-15, or N-13), that has a short decay time.
(bombardment of normal chemicals with neutrons)
PET detects the gamma rays given off at the site where a positron emitted from the
radioactive substance collides with an electron in the tissue.
PET provides images of blood flow or other biochemical functions, depending upon
the type of molecule that is radioactively tagged. For example, PET can show images
of glucose metabolism in the brain, or rapid changes in activity in various areas of the
body. However, there are few PET centers in the country because they must be
located near a particle accelerator device that produces the short-lived radioisotopes
used in the technique.
Schematic of a PET scanner
K. Nikolopoulos (Univ. of Athens) – Recent Developments in Light Detection – July 4th 2005
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Single Photon Emission Computed Tomography
• Single Photon Emission Computed Tomography (SPECT)
SPECT is a technique similar to PET.
– The radioactive substances (Xenon-133, Technetium-99, Iodine-123) have longer
decay times than those used in PET
– Single photon emittance instead of double gamma rays.
• SPECT can provide information about blood flow and the distribution
of radioactive substances in the body.
• Its images have less sensitivity and are less detailed than PET
images.
• SPECT technique is less expensive than PET.
• SPECT centers are more accessible than PET centers because they
do not have to be located near a particle accelerator.
K. Nikolopoulos (Univ. of Athens) – Recent Developments in Light Detection – July 4th 2005
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