How does a lead apron protect someone from x-rays?



I was at the dentist with my daughter this week and she was having some x-rays done. The dental assistant put a lead vest on her and told my daughter it would protect her from the x-rays. Later, my daughter asked me *how* the lead apron protected her.

Does the lead apron reflect the x-rays in some way? Does it absorb it? If it absorbs, is there a limit as to how many times a lead apron can be used before it’s “full” ?

In: Physics

> Does the lead apron reflect the x-rays in some way?

This is the ticket. Lead is very dense and has a large number of electrons, meaning it’s very good at deflecting and scattering radiation.

Think of two different chain-link fences, one with bigger holes than the other. If you throw ping-pong balls at the one with large holes, sure, some will bounce off the wire, but some will go through.

Throw the same ping-pong balls at the smaller fence, and substantially more will bounce off. That’s essentially how lead protects you.

Okay so this is a complex question. Few important points to note:

1) lead is not magic, everything can block radiation, but lead is very dense, has a large number of electrons, has a small atomic radius, and is not toxic (not radioactive as many other dense metals are that is, but it’s toxic in other regards). So you need a lot less thickness of lead to attenuate the same amount of radiation than you would of some other material. And because of this density, an incident electromagnetic wave would have a very high probability of running into a nucleus or some electrons, rather than passing straight through. This attentuates the wave by absorption and scattering (electrons can be knocked off and picked up by another atom or just raised to a higher energy before they descend back down releasing energy in the form of light and some heat), where similar or lower energy waves (in addition to some heat) are emitted in all directions as opposed to the initial focused high intensity wave coming at you. And regarding your question about replacing the apron, well yes eventually lead does degrade after looong use, but it’s more the mechanical properties that degrade and sometimes you get kinks and holes in it making it less effective at some parts, so it’s not really that it gets too soaked with radiation because that energy dissipates.

2) there are maaaaany types of radiation. The stuff we worry about is ionizing radiation which can be divided into electromagnetic and particle radiation. And lead is best at blocking xrays and gamma rays, two very highly energetic electromagnetic or light waves. For some other types of radiation lead is actually very bad for you because it causes secondary emissions that would harm you even more. So that’s important to note here.

3) lead aprons are actually sort of a hot topic these days. Some are arguing they’re not really necessary given the current technology and they may even get in the way of proper medical examinations. But that’s a whole other story so let’s not go off topic.