- Researchers used quantum sensors to accurately measure X-ray emissions from three radioactive elements.
- The measurements reduced uncertainty in X-ray energy by one-third to one-eighth.
- Transition-edge sensors can detect photon counts, enabling highly precise measurements.
- The technology could improve nuclear power plant operations but faces cooling system limitations.
US researchers have successfully used ultra-sensitive quantum sensors to accurately measure X-ray emissions from three radioactive elements: uranium, plutonium, and neptunium. These sensors were developed at the National Institute of Standards and Technology (NIST) in Maryland. The researchers say this technology will significantly improve the monitoring of nuclear materials in power plants and weapons facilities. Radioactive elements are typically identified by their unique gamma-ray emissions, but some elements also produce X-rays within the same energy range, making it more difficult to determine the specific nuclear material and its quantity.
In this project, the researchers measured the X-rays emitted by these three radioactive elements. Their results reduced the uncertainty in X-ray energy by one-third to one-eighth compared to previous measurements. NIST physicist Jonathan Dean stated, "Our measurements support international nuclear safeguards by enabling more accurate accounting of materials in nuclear facilities."
How Quantum Sensors Work
The team used a device called a transition-edge sensor (TES), originally developed at NIST. These sensors function similarly to extremely sensitive miniature thermometers. Each sensor is equipped with a layer of superconducting film that is cooled to an extremely low temperature, near absolute zero. At this temperature, according to the researchers, the film behaves at the boundary between a zero-resistance superconductor and a regular metal with measurable resistance. When a photon, such as an X-ray photon, hits the sensor, it produces a tiny amount of heat, causing the film's resistance to increase rapidly.
Transition-edge sensors can detect the number of photons that strike it.
The magnitude of the change corresponds to the energy of the photon, allowing the team to make highly precise measurements. Using these sensors, the team measured the X-rays from uranium, plutonium, and neptunium, which overlap with gamma-ray emissions in energy. Removing this so-called X-ray background noise would make it easier to determine the proportion of different isotopes in nuclear materials. The isotope ratio can indicate the intended use of the radioactive material. For example, uranium-235 makes up about 0.7% of all natural uranium. Nuclear reactor fuel requires enrichment to a few percent, while weapons-grade uranium can reach about 90%.
More accurate isotope measurements can enhance nuclear material accounting and international safeguards.
Applications and Challenges of the Technology
NIST says this technology could make nuclear power plant operations more efficient. The process of generating power through uranium fission involves several stages. Before proceeding to the next step, it may be necessary to assess the composition of the nuclear fuel. However, faster measurements could shorten these waiting times, thereby improving efficiency and reducing costs. Nevertheless, the technology does have limitations. TES detectors require a cooling system capable of maintaining them at temperatures near absolute zero, making a handheld version impractical. However, these detectors can operate anywhere with sufficient power to run their cooling equipment.
Samples can also be transported to laboratories equipped with the sensors. "Our instrument is compatible with both methods," Dean summarized in a press release.
NIST and Los Alamos National Laboratory have installed TES detectors for nuclear material monitoring in three US Department of Energy laboratories. The technology is also used in major research institutions including CERN, SLAC National Accelerator Laboratory, Argentina's National Laboratory, and Brookhaven National Laboratory. Scientists are currently working on improving the accuracy of the detectors and making their cooling systems more compact, simpler, and cost-effective. NIST has also begun exploring the use of these detectors in fundamental particle research and space science.
The Potential of Quantum Sensors in Nuclear Material Monitoring
The development of this technology marks a significant advance in the use of quantum sensors for nuclear material monitoring. By reducing the uncertainty in X-ray energy, researchers can more accurately identify and quantify nuclear materials, which is crucial for international nuclear safeguards. As the technology advances, it could improve the efficiency of nuclear power plants, reduce costs, and strengthen the monitoring of nuclear materials. However, the need for cooling systems limits its portability, which may affect its application in certain environments.