Predicting how many repelling atoms can be dissolved – Crystal geometry-derived new theory accelerates alloy materials design – 

2026.03.13

The Nuclear Engineering Research Center has developed a mathematical model of dopant elements in order to obtain a universal guideline for alloy materials design.

The arrangement of dopant elements in alloys is a crucial factor to determine the mechanical properties such as strength and corrosion resistance. When repulsive forces act between dopant elements, their arrangement adopts a complex pattern where the elements are distributed uniformly yet not adjacent to each other. Moreover, if the concentration of dopant elements is increased until they finally become adjacent, the mechanical behavior—such as strength (hardness) and toughness (ductility)—can change drastically. For example, in the iron-chromium-aluminum (Fe-Cr-Al) alloy, which is studied and developed for nuclear applications, it is known that the toughness is improved by increasing the Al content until Al atoms become neighbors. Thus, the upper limit of concentration (saturation fraction) of repelling dopant elements is a key parameter for determining the alloy’s composition. However, it is extremely difficult to experimentally probe the atomic-scale arrangement of individual atoms, and a theoretical method for predicting the saturation concentration has been needed.

In this study, we established a new theory, based on numerical simulation and mathematical modeling, that answers the question: “How high can the dopant concentration be raised, if dopant elements are added in order not to be adjacent to each other?” The theory shows that the intricate problem of atomic configuration can be described solely by the universal property of “crystal geometry”, making it a general framework that applies to any material system. Revealing, in a rigorous yet simple analytical form, how far randomly placed atoms can avoid adjacency is a breakthrough result from a scientific standpoint.

Since the established theory does not presume a specific material, it can be employed in the design of a wide variety of alloys. In addition to the Fe-Cr-Al alloys, it can serve as a theoretical guide for determining the elemental compositions of multicomponent systems such as high entropy alloys.

The results of this research have been published in Scientific Reports on 12 March 2026 (local time).
Article information: https://doi.org/10.1038/s41598-025-30829-1

JAEA HP Press release (Japanese only)

World’s First Table-Top System for Non-Destructive Isotope Analysis Using a Fingertip-Sized Neutron Source – Toward On-Site Identification of Nuclear Material Isotopes  – 

2026.02.03

Fig. 1 Comparison between a conventional NRTA system (left) and
the developed table-top NRTA system (right).

Nuclear Science and Engineering Center (NSEC) has developed a prototype system as an important step toward realizing a table-top instrument for the non-destructive assay (NDA) of nuclear material (NM) isotopes. Accurate isotope measurements by NDA are essential for proper nuclear fuel management and the prevention of illicit use of NMs.

NMs such as uranium and plutonium contain multiple isotopes with different neutron numbers. The isotopic composition determines key properties, including suitability as nuclear fuel and potential for weaponization. Therefore, accurately evaluating not only the total amount of NM but also the types and abundances of its isotopes is essential for nonproliferation and nuclear security.

Conventional NDA techniques generally struggle to distinguish isotopes. Although neutron resonance transmission analysis (NRTA) enables isotope identification, it has traditionally required highly specialized infrastructure such as large-scale accelerators or dedicated neutron sources. Consequently, NRTA measurements have been difficult to conduct in space-limited facilities, non-radiation-controlled areas, or outdoor environments. To overcome this limitation, NSEC has established an NRTA technique using a fingertip-sized californium-252 neutron source and developed the world’s first table-top NRTA system that enables isotope identification without the need for large-scale specialized facilities (Figure 1). Test measurements using simulated samples with resonance energies close to those of NMs demonstrated the system’s ability to differentiate isotopes. This result opens the way to nondestructive, on-site isotope measurements in environments where conventional NRTA has been impractical.

This achievement represents an important milestone toward the practical realization of a compact NRTA system capable of isotope measurements of NMs. Future efforts will include validation using actual NMs, improvements in measurement precision, and expansion of the range of measurable isotopes. In addition to contributing to nonproliferation and nuclear security, this technique holds promise for a wide range of applications requiring nondestructive isotope analysis, including age dating and provenance studies in archaeology, as well as the analysis of samples returned from space exploration.

The results of this study have been published in Communications Engineering, an open-access Nature Portfolio journal, on January 23, 2026.
Article information: https://doi.org/10.1038/s44172-025-00564-6

JAEA HP Press release (Japanese only)