Detectors Measuring Ions A beam of charged particles

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. • Separated by liquid argon incident particle depleted uranium ] 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