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Using an electroscope to measure radioactivity

The Curies used Becquerel's idea

It was Becquerel who had discovered that radioactive substances could discharge an electroscope, so the Curies simply developed his ideas.

No one really knew why radioactivity caused an electroscope to discharge

It’s important to realise that no one knew whether radioactivity was due to particles or waves or what.  All they knew was that radioactivity ionized air molecules.

Pitchblende causes more ionization than the pure uranium metal.

How the electroscope discharges

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When the electroscope is charged the plate and the gold leaf are left with a positive charge (because the battery takes away some electrons, which are negative).

The radioactivity causes the air to break up into positive and negative charges.  The negative charges (normally electrons) will the positive charge on the electroscope.

This only shows the principles of the Curies’ apparatus and isn’t correct in its details.

back to Lesson 9: Atoms 3: The Nucleus