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Physics can be difficult to learn, but this blog aims to help you get into physics by connecting your GCSE physics lessons with things you see in the world around you.

Tuesday, 25 October 2011

Helpful Decay

It seems like every time that radioactivity hits the news it’s a bad story, with nuclear power plants bearing the brunt of the public’s distrust of all things radioactive. But you’ve probably got at least one thing in your house that works by radioactive decay, and there are loads of other useful applications too.

I wrote before about radioactive decay here but I didn't calrify the three types, alpha, beta and gamma. They are all created by processes which are very similar, just the end product is slightly different. These rays are characterised by how easy it is to stop them. If you think about a light beam, it’s not stopped at all by thin glass, but a really thick piece of glass will make it much dimmer. And it can’t get through walls or anything solid like that.

These rays are just the same, there are things that they can pass through, and things that stop them. Alpha rays are the weakest, and are stopped by less than a mm of lead, or even a very thick piece of paper. Beta rays need a few cm of lead to stop them and gamma rays need even more. Lead is used as the standard measurement here because it’s a very dense material, offering plenty of bulk to absorb all that radiation.

Firstly, this is good to know if you want to be protected from radiation when you’re working in close quarters with a source. But that’s not all it’s useful for.

Alpha radiation, because it’s so easily stopped, is very often used in smoke alarms as the detecting device. This works with an alpha-source on one side of an air gap and a detector on the other. In normal use, the radiation reaches the detector just fine. But if the air gap fills up with smoke particles, this is enough to stop the rays, and the alarm sounds.

Beta radiation is more commonly used for testing the thickness of things during manufacturing processes. The source is placed one side of the product and the detector on the other. If it gets too thin then too much radiation will get through, and if it gets too thick then not enough will get through. The manufacturing line can then be adjusted accordingly either way.

So, whilst we can easily be led to believe by the news that radiation is bad, in fact it can be quite useful! It’s just a matter of treating it with respect and making sure that nuclear waste is very carefully looked after!

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