Question: Hi John, I believe this is a Chemistry styled question, so I'm asking you; How does lead prevent radiation from passing through it? I was thinking about this because they give you lead shielding when you're getting an X-Ray. Thanks!

John Wenger answered on 12 Nov 2014:

Hi Aaron,

Great question!
X-rays are tiny particles of radiation with lots of energy. They can penetrate skin and flesh but are absorbed by bone, which is a much denser material. So in an x-ray machine you get a contrasting image of your bones because they absorb the X-rays while the flesh around them does not. We have to be careful though because X-rays can damage organs in the body (e.g. kidneys) and a lead shield is used to prevent them from being exposed to the high energy radiation. Lead is used because it a very dense material and absorbs virtually all of the X-ray particles. It is one of the heaviest elements and the atoms are very large. So Looking at it on the atomic level, lead atoms are very close to each other and you can imagine that it will only be a matter of time before the X-ray hits an atom and when it does its energy is transferred to the lead which can then convert the energy to heat and/or light. Other materials could also be used, but lead is cheap and readily available. In principle you could us almost any material to absorb radiation (nuclear reactors use lots of concrete) but the less dense it is, the more of it you would need. So in a practical sense, when having an X-ray it is much better to use a thin lead apron rather than a half metre thick chunk of concrete!

hope that answers your question!

John