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Detecting Radioactivity using a Geiger-Müller Tube.
How is Radioactivity Measured?
Radioactivity is measured in
Becquerels, symbol Bq.
1 Bq = 1 decay per second.
A Geiger-Müller tube displays the amount of radioactivity in Bq.
What is a Geiger-Müller Tube?
tube detects the
ions which are formed by
radioactivity. The tube is filled with argon gas and has a very thin
piece of mica at the end. It is called a mica window, and it lets
all types of radioactivity penetrate through it, even alpha particles.
Below is a picture of a Geiger-Müller tube.
is filled with argon
gas. When an electron is knocked
off an argon atom, a positive ion is formed. The ion is attracted to
the negative inside lining of the tube. When the ion collides with
the tube it collects an electron and becomes an argon atom again.
The electron that was knocked
off is attracted to the
central positive wire. When the electron collides with
the positive wire, the tiny amount of electricity
causes a click from the loudspeaker of the counter.
The counter has a digital display of
the number of clicks per second.
This is the same as the number of radioactive waves or
particles that have entered the tube and made ions in one second.
tube and the counter together are often called
a Geiger counter. The count rate (reading) obtained from a
Geiger counter depends on the distance of the tube from the
radioactive source. The closer the tube is to the source, the
more radioactivity will enter it and the higher the reading will be.
The reading is also affected by the background count.
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