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Suppose one knows almost nothing about the nature of radioactivity (like the discoverers of this phenomenon).

What are the detailed/rigorous logical steps/arguments to show experimentally that radioactive radiation ionizes air?

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Thanks for your answers. The Experiment I had in mind is to discharge an electroscope using radioactive radiation. However then it is not clear, whether air is ionized or radiation discharges the electroscope directly. –  martin Mar 25 '11 at 12:22
    
Pump the air out of the chamber. Does the discharge stop? If so, the air was involved. Vacuum pumps and fittings aren't too expensive, if you're not trying to get really hard vacuum. –  Andrew Mar 25 '11 at 16:12
    
@Andrew, thanks that's a good idea. Do you have a video link where this (or a similar) experiment is performed in vacuum and in air? –  martin Mar 26 '11 at 8:59
    
Are there other ways to see that air is indeed ionized in the electroscope experiment except doing it in vacuum? –  martin Mar 26 '11 at 9:52
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2 Answers

Have a look at the cloud chamber article in wikipedia. It shows that there is ionisation of the air.

Also the discovery of the harmful effects of radioactivity.

Here is how to build your own cloud chamber.

This sort of measurements are repeated in student labs the world over. These are the first researchers in radiation.

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Anna, is Your answer "detailed/rigorous" ? :=) –  Georg Mar 24 '11 at 16:00
    
:) No, but the wiki articles I am referring to are :). Here is how to make your own cloud chamber scienceinschool.org/2010/issue14/cloud . I think I will add it in my answer –  anna v Mar 24 '11 at 16:23
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I would read the Wikipedia article on smoke detectors. Then I would buy a smoke detector, crack one open, and try to build a similar device myself.

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You should treat the guts of a smoke detector with appropriate care. Alpha emiters are quite harmless while outside the body, but if you breath or ingest the stuff the story changes. –  dmckee Mar 24 '11 at 20:06
    
Good call, dmckee! I don't have a lot of experience with radiation safety. I wonder where eating a smoke detector falls on the chart? –  Andrew Mar 25 '11 at 16:13
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