Editing X-ray (section)

===Soft and hard X-rays===
X-rays with high [[photon energy|photon energies]] above 5–10&nbsp;keV (below 0.2–0.1&nbsp;nm wavelength) are called ''hard X-rays'', while those with lower energy (and longer wavelength) are called ''soft X-rays''.<ref name="Attwood">{{Cite book |author= Attwood, David |title= Soft X-rays and extreme ultraviolet radiation |publisher= Cambridge University |date= 1999 |isbn= 978-0-521-65214-8 |url= http://ast.coe.berkeley.edu/sxreuv/ |page= 2 |access-date= 4 November 2012 |archive-url= https://web.archive.org/web/20121111141255/http://ast.coe.berkeley.edu/sxreuv/ |archive-date= 2012-11-11 }}</ref> The intermediate range with photon energies of several keV is often referred to as ''tender X-rays''. Due to their penetrating ability, hard X-rays are widely used to image the inside of objects (e.g. in [[medical radiography]] and [[airport security]]). The term ''X-ray'' is [[metonymy|metonymically]] used to refer to a [[radiographic]] image produced using this method, in addition to the method itself. Since the wavelengths of hard X-rays are similar to the size of atoms, they are also useful for determining crystal structures by [[X-ray crystallography]]. By contrast, soft X-rays are easily absorbed in air; the [[attenuation length]] of 600&nbsp;eV (~2&nbsp;nm) X-rays in water is less than 1&nbsp;micrometer.<ref>{{Cite web |url=http://physics.nist.gov/cgi-bin/ffast/ffast.pl?Formula=H2O&gtype=5&range=S&lower=0.300&upper=2.00&density=1.00 |title=Physics.nist.gov |publisher=Physics.nist.gov |access-date=2011-11-08}}</ref>