To monitor the amount and type of nuclear material at power plants and weapons facilities, scientists look for a special signal—the unique pattern of gamma rays emitted by specific radioactive elements. However, some of these elements also emit X-rays in the same energy range as the gamma-ray emissions, masking the signal and making nuclear stockpiles harder to assess.

Now, researchers at the National Institute of Standards and Technology (NIST) have measured the confounding X-ray emissions from plutonium, uranium and neptunium (a nuclear decay product of uranium) with unprecedented accuracy. This achievement allows scientists to filter out the X-ray background noise so they can more precisely evaluate the accumulation of nuclear materials.

“Our measurements support international nuclear safeguards by enabling more precise accounting of material in nuclear facilities,” said Jonathan Dean, a physicist at NIST and the University of Colorado Boulder.