September 21st is Donald Glaser's birthday. Glaser is an American physicist and neurobiologist who was awarded the 1960 Nobel Prize in Physics for the invention of the bubble chamber.
The bubble chamber is a detection device for particle physics that works on the same basic principle as the cloud chamber. A vessel is filled with a transparent liquid (usually liquid hydrogen) heated to just below its boiling point and aligned with a magnetic field. When the scientist is ready to take a reading, a piston is used to expand the chamber. This causes the liquid to become superheated. Any charged particles passing through the vessel will ionize the liquid and cause bubbles to appear along the particle's path. The bubble density and path shape can give information on the type, charge and lifetime of the particles.
Bubble chambers have been replaced by newer methods of detection in modern particle research laboratories, but they still have a place in demonstrations and education. The photographs taken of bubble trails bring the invisible world of particle physics to a light a student can see, measure and understand. Find out what else occurred on this day in science history.