Editing Ytterbium (section)

===Source of gamma rays===
The <sup>169</sup>Yb [[isotope]] (with a [[half-life]] of 32 days), which is created along with the short-lived <sup>175</sup>Yb isotope (half-life 4.2 days) by [[neutron activation]] during the [[irradiation]] of ytterbium in [[nuclear reactor]]s, has been used as a [[radiation]] source in portable [[X-ray]] machines. Like X-rays, the [[gamma rays]] emitted by the source pass through soft tissues of the body, but are blocked by bones and other dense materials. Thus, small <sup>169</sup>Yb samples (which emit gamma rays) act like tiny X-ray machines useful for [[radiography]] of small objects. Experiments show that radiographs taken with a <sup>169</sup>Yb source are roughly equivalent to those taken with X-rays having energies between 250 and 350&nbsp;keV. <sup>169</sup>Yb is also used in [[nuclear medicine]].<ref>{{cite book|pages=168–169|url=https://books.google.com/books?id=wJqBSA1exqoC| title =Industrial radiology: theory and practice| author= Halmshaw, R. | publisher = Springer| date = 1995| isbn =978-0-412-62780-4}}</ref>