Nuclear bombs are the most destructive weapons humanity has ever devised, but they have an unexpected upside. They’ve contributed to some surprising advances in other scientific fields like neuroscience and climatology. To understand the connection, one must know about carbon-14.
Usually carbon has an atomic mass of twelve; six protons and six neutrons. But on occasion, neutrons energized by cosmic rays from our sun will collide with nitrogen atoms in our atmosphere, knocking a proton off the atom and converting nitrogen into carbon with two extra neutrons, carbon-14. Carbon-14 is radioactive, with a half-life of about 5,700 years.
The thing is, plants use carbon-14 like any other carbon atom during photosynthesis, and that carbon-14 works its way through the food chain. Meaning, everyone has this radioactive isotope spread throughout our bodies. Since carbon-14 is constantly decaying and is replenished by natural cycles, the amount of it in our atmosphere remains pretty constant.
Unless, we set off explosions that release a lot of high energy neutrons into our nitrogen-rich atmosphere like during the nuclear testing of the 50s and 60s.
Atomic bombs create an artificial spike in atmospheric carbon-14, and we can associate that spike to an exact moment in time. Since we know how much carbon-14 was in the air for any given year and we know how carbon works its way into our bodies, we can use these spikes to measure how much carbon-14 is in a cell’s DNA and determine what year that cell was formed.