Should we be strapping these to our torsos?

We’re all a little bit radioactive now. Thanks to atom bomb tests in the mid-20th century, it’s possible to use radioactive (but harmless) carbon-14 to date not only bristlecone pines and putative Noah’s Arks but also, in a recent Karolinska Institutet study, Grandma and Grandpa’s artery fat.

The technique used in this study—radiocarbon dating—is widely employed by archaeologists and geologists to determine when organisms like fossilized trees or plants lived. All organisms absorb carbon-14 along with normal carbon-12 in a ratio that mirrors how much of each type is present in the atmosphere. (Carbon-14 is produced naturally in the upper atmosphere by cosmic rays, and then mixes throughout the atmosphere and into the oceans.) When an organism dies, the carbon-14 starts to decay at a known rate—half the atoms become nitrogen-14 in about 5,700 years—and the amount left in the tissue when it’s dug up can be used to back-calculate its age.

The above-ground atom bomb tests of the Cold War era raised the amount of carbon-14 in the air; after the tests stopped, atmospheric radiocarbon declined at a very precisely recorded rate. Using this information, scientists ...