Question

How does radiation shielding work?

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Answer 1

I assume you are asking about shielding from `gamma` rays, possibly neutrons, since shielding from `alpha` and `beta` particles is easily achieved.

Explanation:

In essence `gamma` rays are quite difficult to shield against as they are not very likely to interact with matter (though that does depended on their energy) meaning they penetrate quite far into ‘normal’ matter e.g. buildings, bodies etc.

There is an increasing likelihood of gamma rays forming electron-positron pairs in the presence of atomic nuclei as their energy rises. (Spontaneous generation of matter (mass) from energy according to Einstein’s famous equation.) It thus makes sense to try to find a material that has a high density whilst not in itself radioactive, prohibitively expensive etc. The common solution is to use lead which is plentiful, easily extracted from its ore due to its low reactivity and easily worked.

There is also a need to use higher levels of absorbers around very intense `gamma` ray sources such as nuclear power stations, particle accelerators etc. and it becomes quite expensive. A cheaper solution is concrete, though around a reactor you may need several cm of lead as well as several metres of concrete to produce the attenuation in intensity required.

Shielding from neutrons requires significantly more complex physics to understand ... firstly they must be slowed from ‘hot’ to ‘thermal’ velocities, next absorbed by low mass nuclei (water, boron are common) and then the secondary radiation from the absorber must itself be absorbed (see above.) Much more detail here if required!