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Detecting Radioactivity using a Film Badge.

How can Radioactivity be Detected?

Radioactivity causes ionisation. The ions formed can be detected
using a photographic film badge or a Geiger-Müller tube.

What is a Film Badge?

A film badge is a thin plastic container which opens at a hinge.
Inside there is a piece of film behind some windows (see below).

People who work with radioactivity (or X-rays) wear a
film badge to monitor their exposure. Radiation will make
photographic film darken in the same way that exposure
to light and X-rays do. The greater the amount of radiation
that the film is exposed to, the darker the film becomes.

What is the Meaning in Physics of the word Window?

People who do physics use the word "window"
for any substance which allows a wave or particle
to pass through it. The glass windows in your
house allow light to pass through them. An aluminium
window would allow gamma rays to pass through.

A film badge has spaces in the plastic in front of the film
containing thin windows of paper, aluminium and lead.

Below is a picture of a film badge.

Film Badge to Detect Radioactivity

When the film is developed it gives an indication of the exposure
to the type and amount of radiation the film badge has received.
You can work out what type of radioactivity will reach the film
behind the different materials by looking at the penetrating ability.

The film badge is a cheap and convenient method of
monitoring exposure to radiation. A Geiger-Müller
tube is a more precise method of measuring radiation.

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