bubble chamber

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun An apparatus in which the movement and collision of ionizing particles is determined by the examination of trails of gas bubbles that form in the paths of the particles as they move through a superheated liquid.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A vessel filled with a superheated transparent liquid (most often liquid hydrogen) used to detect electrically charged particles moving through it.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun an instrument that records the tracks of ionizing particles