Ytterbium
Source of gamma rays

The Yb isotope (with a half-life of 32 days), which is created along with the short-lived Yb isotope (half-life 4.2 days) by neutron activation during the irradiation of ytterbium in nuclear reactors, 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 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 Yb source are roughly equivalent to those taken with X-rays having energies between 250 and 350 keV. Yb is also used in nuclear medicine.
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