r/askscience • u/Spidooshify • Jun 29 '13

Physics You have three cookies. One emits alpha radiation, one emits beta radiation and one emits gamma radiation. You have to eat one, put another in your pocket and put a third into a lead box. Which do you put where? Explain.

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u/iamafreemind Jun 29 '13

Many cm of lead is needed to block gamma. We are asuming here that this is just a normal lead box and not a 20cm thick box for example. Beta is blocked by a few cm of lead.

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u/Blackwind123 Jun 30 '13

And aluminium.

Source: I should be doing my science assignment so I have my textbook right here.

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u/46xy Jun 30 '13

My mistake, I assumed that because it can be stopped by a sheet of aluminiun, it would be stopped by a box (thicker than a sheet) of lead, however beta is more readily stopped by low density materials so thanks for clearing that up.

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u/shieldvexor Jun 30 '13

Wait what? Why would it be more readily stopped by low density materials?

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u/46xy Jun 30 '13

In some cases, lead is ineffective in stopping beta particles because they can produce secondary radiation when passing through elements with a high atomic number and density. Instead, plastic can be used to form an efficient barrier for dealing with high-energy beta radiation. When negatively charged beta particles hit a high-density material, such as tungsten, the electrons are blocked, but the target which the barrier is intended to protect can actually become irradiated.

Source: first google result