# How come X-ray can see through matter if its wavelength is shorter than visible light?

**URL:** <https://boards.straightdope.com/t/how-come-x-ray-can-see-through-matter-if-its-wavelength-is-shorter-than-visible-light/717577>\
**Category:** Factual Questions\
**Created:** [April 13, 2015, 5:12pm UTC](https://boards.straightdope.com/t/how-come-x-ray-can-see-through-matter-if-its-wavelength-is-shorter-than-visible-light/717577 "2015-04-13T17:12:00Z")\
**Posts on this page:** 1\
**Page:** 2

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**Author:** ![Pasta](https://avatars.discourse-cdn.com/v4/letter/p/ecccb3/32.png) [@Pasta](https://boards.straightdope.com/u/Pasta)\
**Post date:** [April 17, 2015, 4:03am UTC](https://boards.straightdope.com/t/how-come-x-ray-can-see-through-matter-if-its-wavelength-is-shorter-than-visible-light/717577/21 "2015-04-17T04:03:39Z")

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There is a nifty online tool that I use from time to time: [NIST XCOM Photon Cross Sections Database](http://physics.nist.gov/PhysRefData/Xcom/html/xcom1.html). You can plug in any mixture or compound and a range of incident photon energies, and it will give you a plot and text-based spreadsheet of the photon attenuation, optionally broken down by physical process. Folks interested in this thread might be interested in playing with this tool.

Here is [an example graph](http://i.imgur.com/8cTVgbu.png) for water covering energies from 1 keV to 10 MeV. You can see that as you move through the energies, the physical processes that dominate vary. For medical imaging x-rays, Compton scattering (labeled “incoherent scattering” in the graph) and photoelectric absorption are the dominant processes.

For kicks, [here’s calcium](http://i.imgur.com/X30Hhep.png), showing one of its [K edges](http://en.wikipedia.org/wiki/K-edge).

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