Marie Curie (1867-1934) shows that thorium is radioactive and hypothesizes that radioactive emanations come from single atoms
Citation:
Editors. "Theory of radioactivity starts being developed by Marie Curie".
The Literary Encyclopedia. First published 01 May 2009
[http://www.litencyc.com/php/stopics.php?rec=true&UID=6382, accessed 22 May 2013.]