See also: # Soft X-Rays vs. Hard X-Rays Motivation: I read a thing in [[@shyCramerRaoBound2022]] and got confused. >"Soft X-Rays carry far less energy than hard X-Rays, and are for this reason more easily absorbed by air and especially by other mediums. In water, the majority of soft X-ray photons will be absorbed before they have travelled even a millionth of a meter." [^1] So basically, hard X-rays are just X-rays with higher energies, and are called hard because they are more penetrating. this language is especially used in [[Radiography]] contexts. [^1]: https://www.anl.gov/article/7-things-you-may-not-know-about-xrays#:~:text=There's%20a%20big%20difference%20between,a%20millionth%20of%20a%20meter.