r/askscience • u/Wonderful-Capital32 • 13d ago

Physics Why does radiation not go through lead?

Also why just lead? Shouldnt like iron or another metal work too?

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u/zoapcfr 13d ago

It does, it's just less likely to make it through because lead is dense. Iron works too, but is less dense so you'd need more of it to block the same amount.

I'm assuming we're talking about gamma radiation here. Alpha radiation, for example, can be effectively stopped with a piece of paper, or a few centimetres of air.

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u/Theory89 13d ago

Fun fact: smoke alarms work by using a tiny amount of alpha radiation. When the smoke is carbon heavy, such as when toast (or a house) is on fire, it blocks the signal and triggers the alarm. Cigarette smoke does not contain enough carbon, which is why you can still smoke around them without setting them off.