6 - Historical track detectors

Summary

A man should look for what is, and not for what he thinks should be.

Albert Einstein

In this chapter some historical particle detectors will be briefly described. These are mainly optical devices that have been used in the early days of cosmic rays and particle physics. Even though some of these detectors have been ‘recycled’ for recent elementary particle physics experiments, like nuclear emulsions for the discovery of the tau neutrino (v_T) or bubble chambers with holographic readout for the measurement of shortlived hadrons, these optical devices are nowadays mainly integrated into demonstration experiments in exhibitions or employed as eye-catchers in lobbies of physics institutes (like spark chambers or diffusion cloud chambers).

Cloud chambers

The cloud chamber (‘Wilson chamber’) is one of the oldest detectors for track and ionisation measurement [1–4]. In 1932 Anderson discovered the positron in cosmic rays by operating a cloud chamber in a strong magnetic field (2.5 T). Five years later Anderson, together with Neddermeyer, discovered the muon again in a cosmic-ray experiment with cloud chambers.

A cloud chamber is a container filled with a gas–vapour mixture (e.g. air–water vapour, argon–alcohol) at the vapour saturation pressure. If a charged particle traverses the cloud chamber, it produces an ionisation trail.