Detectors and the Particle Physicist

Detectors are devices used by elementary particle physicists in the search for a greater understanding of the subatomic particles which make up the universe. As well as detecting charged particles, detectors can be used to detect radiation, making them a useful tool in other aspects of science such as in nuclear physics experiments, nuclear medicine and geological exploration.

A wide range of detector devices exist, such as the cloud, bubble and proportional chambers. All detectors work based on the same fundamental principle: the transfer of all or part of the particle or radiation energy to the detector mass, where it is converted into some other form more accessible to human perception.

The form in which the converted energy appears depends on the detector and its design. Gaseous detectors such as drift and multiwire proportional chambers (MWPC) output a current signal, whilst scintillation counters output a light pulse. Modern detectors are essentially electrical in nature and output electrical impulses, which are readily analysed by electronic means.

Before the development of the proportional and drift chambers during the late 1960's, the spark chamber was widely used as a triggerable track detector. The spark chamber itself was a development of the spark counter.

The spark counter consisted of a pair of parallel plates with a high potential difference between them, in a gas atmosphere, used in the same way as a Geiger Muller tube. The main difference between the spark counter and the spark chamber was the use of photographic rather than electrical recording, thus converting the device from a counter to a track locating device.

In modern research detectors of higher sophistication are used which have a combination of higher spatial and temporal resolution, increased efficiency and readout time, along with a reduced 'dead time'

A table of some detectors and their characteristics is given below:

Detector Type

Resolution Time

Dead Time

Bubble Chamber 1ms 50ms
Spark Chamber* a few ms a few ms
Proportional Chamber 50ns 200ns
Drift Chamber 2ns 100ns
Scintillator 150ps 10ns
Silicon Strip <15ns* unknown

* Based on the Spark Chamber built at the University of Birmingham

* The resolution time for the silicon strip is at present limited by properties of the readout electronics, the figure quoted is that which is planned for the SDC silicon tracker.

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