# Page:Popular Science Monthly Volume 87.djvu/130

It is of interest to note that in the majority of cases a radioactive element breaks up in only one way which is characteristic for all the atoms of that element, and gives rise to only one new product. The work of Fajans and Marsden, however, has clearly shown that in the case of radium ${\displaystyle {\ce {C}}}$ and the corresponding products in the thorium and actinium series, the atoms break up in two distinct ways and give rise to two distinct radioactive elements. It has already been pointed out that actinium is in reality one of these side or branch products. It is supposed that uranium ${\displaystyle {\ce {X}}}$ breaks up in two distinct ways, the smaller fraction giving rise to actinium. The evidence, however, on this point, is not yet complete.