Actinium-225 medical radioisotope held in a v-vial at ORNL. The blue glow comes from the ionization of surrounding air by alpha particles.
<a rel="nofollow" class="external text" href="https://www.flickr.com/people/37940997@N05">Oak Ridge National Laboratory</a>
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<a rel="nofollow" class="external text" href="https://www.flickr.com/photos/oakridgelab/31481701837/">Medical radioisotopes</a>