What sensors does a geiger counter have?

Answer 1

One Geiger-Muller tube. This is a low pressure gas filled cold cathode electron tube operated by avalanche ionization. The cathode is a thin walled metal cylinder, the anode is a stiff metal wire running down the central axis of the cylinder, if the tube is to be sensitive to alpha radiation the far end is capped with a single thickness of mica, the near end of the tube is capped and a 2 wire cable runs from there to the counter. When a particle of ionizing radiation enters the tube it triggers an ionization avalanche between the cathode and anode with a current gain around 10,000 (10,000 negative ions hitting the anode for each ionizing particle entering the tube with an equal number positive ions hitting the cathode). The counter then counts these pulses of current to estimate the level of radioactivity.