spark chamber

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

• noun A device consisting of electrically charged parallel metal plates in a chamber filled with inert gas, used to detect and measure a charged subatomic particle as it passes through the chamber, leaving a trail of sparks.

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

• noun an instrument that detects ionizing radiation from elementary particles