Nuclear bomb debris can reveal blast size, even decades later

A new type of fallout forensics can reconstruct nuclear blasts decades after detonation. By measuring the relative abundance of various elements in debris left over from nuclear explosions, researchers say they can accurately estimate the amount of energy released during the initial blast.

As proof of concept, the researchers estimated the yield of the 1945 Trinity nuclear test in New Mexico — the world’s first detonation of a nuclear device. The work pegged the explosion as equivalent to 22.1 kilotons of TNT, close to the official estimate of 21 kilotons. Applying the method to modern blasts could help regulators identify nuclear tests long after the fact and better enforce nonproliferation treaties, the researchers propose in a paper to appear in the Proceedings of the National Academy of Sciences the week of July 4.

Regulators currently monitor nuclear tests by detecting tremors and radioactive material emanating from blasts. Those effects are short-lived, however, so the techniques can only be used within a few days or weeks of a test.

Chemist Susan Hanson and colleagues at New Mexico’s Los Alamos National Laboratory looked at the element molybdenum in glassy debris created by the Trinity test. Stable molybdenum forms when zirconium from the bomb’s fireball radioactively decays. The relative abundance of different molybdenum isotopes created from this process differs from that found naturally. By measuring the overabundance of certain molybdenum isotopes, researchers can determine the original amount of zirconium created by the explosion. Pairing the amount of remnant plutonium in the debris with the zirconium estimate, the researchers can estimate a blast’s explosive yield.

The Los Alamos group declined to comment on the method’s usefulness for measuring the yield of more recent nuclear tests, such as the test North Korea conducted in January (SN Online: 1/6/16).