This occurs in the very heaviest nuclides of all. This decay is not unique, other nuclides can also be formed. The only absolute requirement is that the charge must be balanced and the mass number must be balanced. The oldest method is a simple photographic plate. An accidental expose of photographic plates to a uranium salt was observed by Becquerel, leading to the discovery of radioactivity.
Some substances absorb the energy of the radiation and re-emit the light in the visible spectrum.
This is called fluorescence. The amount of fluorescent light emitted depends on the amount of radiation emitted, leading to a method of quantitatively determining the amount of radiation. When radiation passes through the air in the chamber, it ionizes the particles by knocking off electrons. These charged particles attract the vapor molecules, causing condensation and a trail of condensed liquid, something like a jet trail in the sky. If a chamber filled with gas is exposed to radiation, the gas is ionized to positive ions and electrons by the radiation.