• Question: how does a Geiger counter work

    Asked by petrolhead918spyder to James, Joe, Leonie, Olivia on 18 Mar 2015.
    • Photo: James Pope

      James Pope answered on 18 Mar 2015:

      Hi petrolhead918spyder,

      A Geiger counter works by counting the radioactive particles (alpha and beta particles) and rays (gamma rays) that are emitted by radioactive material. These particles and rays are emitted as a radioactive material breaks down.

      Inside the detector is a tube called an ionisation tube. In this tube the particles cause an electrical pulse to be generated (I’m not sure how) and this pulse then displays on the screen of the counter.

      The more radioactive the material or the larger the amount of radioactive material the higher the count and the larger the pulse.

      The first Geiger Counters were silent, the clicks were added later I think because of them first appearing in films. They appeared in films because the audience couldn’t see the count screen and it seemed like a good idea so got incorporated into the design.

    • Photo: Leonie Oostwoud Wijdenes

      Leonie Oostwoud Wijdenes answered on 18 Mar 2015:

      I didn’t know this, thanks James for explaining

    • Photo: Joe Spencer

      Joe Spencer answered on 18 Mar 2015:

      To add to James excellent answer. Inside the tube bit there’s an inert gas, like helium. Whicha voltage is applied. When an ionising particle or gamma photon causes ionisation in the gas it allows charge to move, essentially completing the circuit meaning you get an electrical impulse.

    • Photo: Olivia Lynes

      Olivia Lynes answered on 18 Mar 2015:

      I’d forgotten all of that! We had them in school and I think we tested the radioactivity of lots of different items, including a banana.

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