Quantum sensors cut X-ray measurement uncertainty by up to 8× at US

Eightfold reductions in X-ray measurement uncertainty have been achieved at US nuclear facilities using quantum-based transition edge sensors (TESs), according to new findings from the National Institute of Standards and Technology (NIST). The devices enabled precise identification of X-ray emissions from uranium, plutonium, and neptunium—three radioactive elements whose signals overlap with gamma-ray energies.

The sensors were designed at NIST’s Maryland campus. Researchers state they hold potential to significantly strengthen nuclear material monitoring across power plants and weapons-related facilities. Radioactive elements are conventionally identified via their unique gamma-ray signatures. Yet certain isotopes emit X-rays within identical energy bands, introducing ambiguity in both material identification and quantitative analysis.

In controlled experiments, the team measured X-ray emissions from all three elements. Their results narrowed uncertainty in X-ray energy values by factors ranging from one-third to one-eighth relative to prior measurements. “Our measurements support international nuclear safeguards by enabling more precise accounting of material in nuclear facilities,” said Jonathan Dean, PhD, a NIST physicist.

Tiny energy changes

The researchers deployed transition edge sensors originally developed at NIST. Each functions as an ultra-sensitive micro-thermometer. Its core consists of a superconducting film cooled to within a fraction of a degree above absolute zero.

At that temperature, the film rests precisely at the phase boundary between superconductivity—where electrical resistance vanishes—and normal metallic conduction—where resistance is measurable. When a single X-ray photon strikes the sensor, it deposits a minute quantity of heat. That thermal input triggers an immediate, quantifiable rise in the film’s electrical resistance.

The magnitude of the resistance shift directly correlates with the photon’s energy, permitting high-resolution spectral measurement. Using this principle, the team captured X-ray data from uranium, plutonium, and neptunium across energy ranges that coincide with gamma-ray emissions.

Eliminating this X-ray background noise could improve resolution of isotopic ratios in nuclear samples. Such ratios serve as indicators of intended use: uranium-235 constitutes approximately 0.7 percent of natural uranium; reactor fuel requires enrichment to several percent; weapons-grade uranium contains roughly 90 percent.

More accurate isotopic quantification would therefore reinforce nuclear material accounting protocols and bolster international safeguards frameworks.

Faster nuclear fuel checks

NIST reports the technology may accelerate verification procedures at nuclear power plants. Uranium-fueled electricity generation involves sequential operational stages, each requiring confirmation of fuel composition before proceeding.

Shorter measurement durations could compress these verification intervals, increasing plant efficiency and lowering operational costs. However, TES detectors depend on cryogenic refrigeration systems capable of sustaining temperatures near absolute zero—rendering handheld deployment impractical.

Nonetheless, the sensors operate wherever sufficient electrical power supports their cooling infrastructure. Alternatively, samples can be transported to fixed laboratories housing the equipment. “Our instruments are compatible with both approaches,” Dean stated in a press release.

NIST and Los Alamos National Laboratory have already installed TES detectors at three US Department of Energy laboratories for nuclear material monitoring. The technology is also in active use at CERN, SLAC National Accelerator Laboratory, Argonne National Laboratory, and Brookhaven National Laboratory.

Scientists are now pursuing enhancements to detector accuracy and are working to reduce the size, complexity, and cost of the refrigeration systems. NIST has additionally begun evaluating applications in fundamental particle physics and space science research.