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