Why does higher frequency radiation penetrate deeper?

[LogicalAcid]

Than lower frequency radiation, for example, X rays pass through skin, but are absorbed by bone. Whether this is a property of the substance, or of the radiation, I don't know

 

[cragar]

I think you might be able to say that x-rays have a smaller wavelength so it is less likely for it to interact with the matter. But I am not sure i hope some one can give you a better answer.

 

[Dale]

It is not generally true. For instance, humans are rather opaque to visible light but transparent to radio waves, so radio waves penetrate deeper than visible light despite being lower frequency.

 

[cjameshuff]

It is not generally true. For instance, humans are rather opaque to visible light but transparent to radio waves, so radio waves penetrate deeper than visible light despite being lower frequency.

And glass is fairly good at blocking UV, and Earth's atmosphere is opaque to most UV and to x-ray/gamma ray wavelengths. A more visible example: red light penetrates flesh much better than blue. Hold up your hand to a bright light to see this.

A rather different mechanism, but mix a little milk into a glass of water and shine a light through it...look at the color of the light that passes through. Or look at the sky in the morning or afternoon.

 

[LURCH]

Generally speaking, transparency canhappen when a high frequency wave passes through atoms too small to interact with it, or a low frequency wave passes through atoms too big to interact with it. This makes x-rays particularly usefull for medical applications, because their frequency is too high to interact with the water and proteins that make up most of human soft tissue, but they can be blocked by calcium and carbon.

By counterpoint, the radio waves that DaleSpm mentioned are too low-frequacny (too low-energy) to interact with bone, and so they pass through both bone and soft tissue.

 

[MagnetDave]

What you have is what is known as "competing effects."

For instance: x-rays penetrate a human body easily because they are high enough frequency that most dielectric effects have relaxed out - meaning they can't respond faster enough to the incoming wave. So the only thing that really affects x-rays is nuclear mass. That's why bone (which is more dense and contains heavier nuclei) is a better x-ray absorber (or scatterer) than soft tissue.

However, as you get to things like visible light, these dielectric effects start kicking in, and now you have lots of absorbtion modes. BUT you get down to extreme long waves, like radio and farther, and suddenly most common objects become too small for the wave to "see." (Rule of thumb: radiation does not meaningfully interact with objects on a smaller scale than its wavelength) So now, you can have low frequency stuff penetrating miles into things that would have long absorbed x-rays. Also, you find when you study radio transmission that the atmosphere has "windows" where certain wavelengths are strongly absorbed and others are not. For instance, standard RF (from 10-40GHz, let's say) goes through the atmosphere quite nicely, thank you very much. You climb up in frequency to THz, and it gets just shut down by water vapor, and makes it mere inches into the air. Keep on climbing to the visible range, and we're all good again.

You see this concept a lot in physics where in one zone you have one dominant effect that drops out, but a new one picks up.