Physics

Hydrogen Bubble Chamber

Bubble chambers have played an important role in experimental particle physics, yielding images that can be beautiful as well as informative. This image shows the interactions of a beam of particles in the first of many bubble chambers at CERN, Europe's centre for research in particle physics, near Geneva.

The chamber, only 30 cm in diameter, was filled with liquid hydrogen - the simplest "target" material, as the nucleus of a hydrogen atom consists of a single proton. Here, the particles in the beam, which comes in from the left, are pions, the short-lived particles discovered originally in cosmic rays. One has interacted with a proton in the liquid near the upper left, to create a spray of new particles. One of these was a neutral (uncharged) particle, which left no track, but revealed its existence when it decayed nearer the centre of the image, to produce two charged particles that leave behind a sideways V shape.

The chamber was located in a magnetic field, which made positive particles curve to the right, and negative particles to the left. Particles with high energies, including the beam particles, curve almost imperceptibly, but particles with lower energies produce fascinating spirals. These are mainly due to electrons knocked from atoms in the liquid hydrogen.

From their invention by Donald Glaser in 1952, bubble chambers featured in many experiments through to the 1980s. Glaser was rewarded with the Nobel Prize for Physics in 1960 for his invention.

Credit: CERN Photo