Detectors

Measuring Ions  A beam of charged particles will ionize gas. Particle energy E Chamber area A  An applied field will cause ions and electrons to separate and move to charged plates. Applied voltage V Measured current I I V   A E

Cylindrical Chamber  Cylindrical geometry is common for counters. Grounded outer cathode High voltage anode  The avalanche is limited to a region near the wire. I V  

 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 Single Track

Multiwire Proportional Chamber  An array of proportional readout wires can be placed in an array. Invented in 1968 by Georges CharpakInvented in 1968 by Georges Charpak Used in many discoveriesUsed in many discoveries Received the 1992 Nobel PrizeReceived the 1992 Nobel Prize  Provides excellent position resolution for charged particle tracks.

Uranium Cell  Liquid noble gases can be used in ionization chambers. Liquid argon, krypton, xenon  Uranium plates are alternated with readout pads. Separated by liquid argon  Readout on printed circuit boards. Outer readout pads Inner layer readout wires Ground planes to reduce crosstalk 4.0 mm 2.3 mm 4.3 mm depleted uranium liquid Ar gaps readout pad incident particle

Scintillation Detector  Scintillation detectors rely on the emission of photons from excited states. CountersCounters CalorimetersCalorimeters 1. An incident photon or particle ionizes the medium. 2. Ionized electrons slow down causing excitation. 3. Excited states immediately emit light. 4. Emitted photons strike a light- sensitive surface. 5. Electrons from the surface are amplified. 6. 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 dynodeSometimes 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