# Would my house's wall stop gamma rays?

I'm wondering if there is a material which is able to stop all the electromagnetic spectrum's radiations. Something able to stop every electromagnetic radiation from the ones with the lowest frequency up to the one with the highest.
Intuitions tells me that it may depend on material density, as well as its thickness, but I couldn't find confirmation yet.
Are there any common material/element that are able to do it?
Are standard house walls able to stop them?
I would love some examples, like a paper of "this material", which is "this thick"...

• No, standard walls won't stop gamma rays. Unless you live in a very deep cave, you won't be able to prevent all electromagnetic radiation getting into your living space. Read this article: nuclearconnect.org/know-nuclear/science/protecting – user154420 Jul 1 '17 at 11:42
• – Kyle Kanos Jul 1 '17 at 11:47
• Thanks for sharing related questions. I'm gonna read them, and if they answer my doubts, I'm gonna delete the question! – Gabriele Scarlatti Jul 1 '17 at 11:53
• You can answer your own question instead of deleting it. – Yashas Jul 1 '17 at 16:42
• I don't know very much how to handle this situations yet! I thought that deleting it was a smart move in order to not create duplicates, if the "forum tradition" is to answer it anyway, I'll be glad to do it when I'm able to! Anyway, at the moment I haven't found any other post that answer my doubts so I'll leave it as it is. :) – Gabriele Scarlatti Jul 1 '17 at 16:49

Whether or not a material stops or admits EM radiation is not an all-or-nothing affair. As you surmise, it depends on both material and on the frequency of radiation directed thereat, but what also holds is that all EM radiation will penetrate most everything to at least some depth which depends on both the frequency and the material type, which is characterized by a parameter known as the optical depth and, moreover, this depth is not all-or-nothing either: if $$\mathrm{OD}(m, f)$$ is the optical depth of a material of type $$m$$ and frequency $$f$$ of directed radiation against that material, then what that represents is the thickness of material which will cut the radiation intensity by a factor $$\frac{1}{e}$$, or about 63%. For example, if the optical depth is 1 mm, then the radiation directed against that material will be cut to 37% in the first 1 mm of material, then to 23% in the second 1 mm (2 mm of material "elapsed"), 15% in the third 1 mm (3 mm thick), and so forth, i.e. it's an exponential decay curve:

$$I(I_0, m, f, d) := I_0 \cdot e^{-d/\mathrm{OD}(m, f)}$$

where $$I_0$$ is the incident radiation intensity and $$I$$ is that at depth $$d$$ into the material. Every material has an optical depth greater than absolutely zero, even ones normally considered completely opaque like metals: in that case, it is related to what is called their "skin depth", and for visible light it is on the order of a wavelength.

Moreover, metals provide a good example to consider with regard to gamma rays specifically: generally speaking, a metal's skin depth (hence $$\mathrm{OD}(m, f)$$) is a decreasing function of the frequency $$f$$, i.e. higher frequencies penetrate less. But, above a certain point, which is called the metal's plasma frequency, the ability to absorb the radiation drops precipitously. Effectively, the reason the metals absorb radiation at lower frequencies is their copious highly mobile electrons are very responsive to the stimulation from the EM waves, but above a certain point, they are unable to move fast enough to keep up with the high-frequency oscillations and let it through. This frequency is around the petahertz (PHz) range, while gamma rays are in the exahertz (EHz) range or higher, i.e. greater than 1000 PHz, and typically more than $$10^5$$ PHz, and hence transmitted.

Your house's walls, if made of wood, are generally speaking very transparent to most gamma radiation, i.e. the optical depth is very large and considerably in excess of the typical wall thicknes. However, they are not absolutely so: while their optical depth may be "large", it is not infinite and hence some gamma rays will be absorbed. That is, they will "stop" them, just not stop very many, and probably not stop enough if, say, there was a nuclear blast outside close enough to be in the prompt gamma range, however in most cases that also means you are close enough the house and you will be vaporized in the heat and blast wave and hence you aren't going to worry about this (or anything else, for that matter). On the other hand, it COULD be a concern with a VERY small (not a mistake - as the devices get larger, blast and heat effects increase their lethal distance much faster than prompt radiation effects) device, like that a terrorist might use.