scintillation counter

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

• noun A device for detecting and counting scintillations produced by ionizing radiation.

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

• noun physics A detector of particles and ionizing radiation which uses a photomultiplier to generate flashes of light

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

• noun counter tube in which light flashes when exposed to ionizing radiation