History of Particle Detectors

Scintillator, Photomultiplier History of Detectors Geiger Counter Cloud Chamber Emulsion Scintillator, Photomultiplier Bubble Chamber Spark Chamber Drift Chamber Silicon Detector Image and Logic, A Material Culture of Microphysics - Peter Galison

Geiger Counter This tube is filled with inert gas. The outside walls of the tube form a cathode. Wire down the center acts as the anode. http://en.wikipedia.org http://zencybernaught.blogspot.com Radiation passing through the tube ionizes the gas. Ionized gas accelerates toward the walls and collides with other gas atoms creating an avalanche of particles. Discharges are counted as “clicks.”

Cloud Chamber Ionizing radiation passes through a supersaturated vapor. Radiation disturbs the vapor and causes it to condense. Tracks form along the particle’s path. http://www-outreach.phy.cam.ac.uk Tracks can be seen in real time. Plans are abundant on the Internet for a classroom detector. Materials needed include dry ice and methanol.

Emulsion Plates Photosensitive material is exposed to radiation. Plates are developed and magnified. Advantages over cloud chambers: Images are permanent. Length of the tracks show lifetimes. http://nobelprize.org/educational/physics

Scintillator & Photomultiplier Scintillating materials emit light when a charged particle passes through. Photomultipliers collect the light for analysis. Materials often contain more than one color which helps light reach photomultiplier before being reabsorbed.

Bubble Chamber A bubble chamber is similar to the cloud chamber but uses superheated liquid instead of vapor. Particles passing through the liquid leave tracks. It is equipped with high-speed cameras. Large pistons allowed pressure to be adjusted rapidly. It has a significantly increased rate of collisions.

Spark Chamber Metal plates are surrounded by inert gas. Charged particles pass through the chamber. High voltage is triggered. Sparks between the plates follow the path of the particle. http://www.physics.buffalo.edu/ubexpo/Cosmic%20Rays.html Replaced by more accurate detectors today, some spark chambers are still used due to their simplicity.

Drift Chamber A drift chamber is like a large number of Geiger tubes. An array of wires is stretched across a chamber filled with gas. The ionized gas and electrons produce a current in the wires. Drift chambers track the path of particles in real time.

Silicon Detectors The detector contains doped semiconductors. Charged particles produce a current. These detectors have better resolution but suffer from radiation degradation.

Modern Detectors LHC detectors use a combination of silicon detectors, scintillators, and drift chambers. Physicists choose a combination of these subsystems to optimize detector speed, accuracy, and durability.

To Learn More… http://teachers.web.cern.ch/teachers/archiv/HST2005/bubble_chambers/BCwebsite/index.htm http://cms.web.cern.ch/cms/Education/index.html http://www.atlas.ch/teachers.html http://ed.fnal.gov/lsc/index.shtml http://microcosm.web.cern.ch/microcosm/Welcome.html