An instrument for measuring radon
from air samples.
In geology, this device is usually used in shallow boreholes. The filtered gas is dried and passed to an ionization chamber or scintillation counter: here gamma rays are measured by counting the flashes they produce on a screen, which is usually coated with zinc sulphide.
The alpha particle activity produced from this procedure is used to measure the amount of Radon-232 present in the sample.