a small device with a fluorescent screen, for visually observing the scintillations produced by the impact of alpha rays given off by a radioactive substance
Origin:
< Gr spintharis, a spark + -scope
See spinthariscope in American Heritage Dictionary 4
noun
A device for observing individual scintillations produced by ionizing radiation, as one consisting of a tube with a magnifying lens at one end and a phosphorescent screen and speck of radioactive salt at the other.