Transcript Detectors
Detectors
Measuring Ions
A beam of charged particles
will ionize gas.
I
E
• Particle energy E
• Chamber area A
+
A
-
An applied field will cause ions
and electrons to separate and
move to charged plates.
• Applied voltage V
• Measured current I
V
Cylindrical Chamber
Cylindrical geometry is
common for counters.
I
+
-
V
• Grounded outer cathode
• High voltage anode
The avalanche is limited to a
region near the wire.
Single Track
A single track in a chamber
creates many avalanches.
• All contribute to one pulse
Timing is based on first
avalanche arrival.
• Usually nearest point in the
field
Multiwire Proportional Chamber
An array of proportional readout
wires can be placed in an array.
• Invented in 1968 by Georges
Charpak
• Used in many discoveries
• Received the 1992 Nobel Prize
Provides excellent position
resolution for charged particle
tracks.
Uranium Cell
Liquid noble gases can be used in
4.0 2.3 4.3
mm mm mm
ionization chambers.
•
Liquid argon, krypton, xenon
Uranium plates are alternated with
readout pads.
•
incident
particle
depleted
uranium
Separated by liquid argon
Readout on printed circuit boards.
• Outer readout pads
• Inner layer readout wires
• Ground planes to reduce crosstalk
readout
pad
liquid Ar
gaps
Scintillation Detector
Scintillation detectors rely on
the emission of photons from
excited states.
• Counters
• Calorimeters
1. An incident photon or particle
2.
3.
4.
5.
6.
ionizes the medium.
Ionized electrons slow down
causing excitation.
Excited states immediately
emit light.
Emitted photons strike a lightsensitive surface.
Electrons from the surface are
amplified.
A pulse of electric current is
measured.
Photomultiplier Tube
A photomultiplier tube
(phototube, PMT) combines a
photocathode and series of
dynodes.
The high voltage is divided
between the dynodes.
Output current is measured at
the anode.
• Sometimes at the last dynode
Multipart Detector
Multiple detectors are used to
identify different particles.
Tracking chambers to measure
position.
Calorimeters to measure
energy.
Muon from top decay