Bubble-chamber track

A bubble-chamber track is a line of growing vapor bubbles seeded by ionization along a charged particle path in a superheated liquid. The bubbles scatter illumination and can be photographed from multiple directions to reconstruct the path in three dimensions.

In a known magnetic field, curvature constrains the particle's momentum and the sign of its electric charge; increasing ionization toward a stopping point can add information about energy loss. Bubble size and photographic blur set the visible trail width, so that width is not the particle's physical diameter. Neutral particles can remain invisible until an interaction produces charged secondaries.