NIST-developed transition-edge sensors measured interfering X-ray emissions from uranium, plutonium and neptunium with reduced uncertainty, enabling a more precise basis for gamma-ray analysis of nuclear material. The work centers on sensor performance improvements that reduce ambiguity in spectroscopic readings where multiple isotopes can generate overlapping signals. For nuclear forensics and safeguards stakeholders, lower measurement uncertainty can directly improve material identification confidence and downstream decision-making about detection and characterization. While this is not a therapeutic development, it is a high-impact measurement advance for healthcare-adjacent security systems, including monitoring regimes that intersect with regulated radioactive material logistics.