This leads to a spontaneous-fission half-life of about 10 16 years. However, as the atomic number becomes higher, the potential barrier becomes smaller and eventually disappears, causing the heaviest ...

MELISSA BLOCK, Host: Now, there are some elements, such as gold and aluminum, that do have stable weights. Others are radioactive and have no standard atomic weight, such as radium.

So, now instead of carbon listed as being 12.0107 atomic mass units with a measurement uncertainty of about 0.0008, it has an official atomic weight of [12.0096; 12.0116], where the brackets and ...