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2026.04.13
As an outcome of collaborative research with the National Institutes for Quantum Science and Technology (QST), the cosmic-ray behavior analysis model “PARMA,” developed by the Nuclear Science and Engineering Center of the Japan Atomic Energy Agency (JAEA), has been adopted in the “UNSCEAR 2024 Report” issued by the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR). This has made it possible to evaluate public exposure doses from cosmic rays worldwide with greater reliability than before.
Because exposure doses from cosmic rays vary significantly depending on altitude, latitude, and solar activity, they cannot be evaluated under a single uniform set of conditions on a global scale. In previous UNSCEAR reports, simplified estimation methods based on limited measured data and representative values were used. However, such approaches had the limitation that they could not adequately reflect regional differences or actual living conditions.
The PARMA model developed by the Nuclear Science and Engineering Center is an analytical model constructed on the basis of atmospheric cosmic-ray transport analyses performed with PHITS. It can rapidly calculate cosmic-ray intensity and exposure dose for any location on Earth according to altitude, latitude/longitude, and date. The PARMA model is publicly available online and can be used by anyone. In the UNSCEAR 2024 Report, PARMA was adopted as “the most reliable model currently available.” This means that the radiation transport analysis technology that JAEA has developed over many years has been recognized as a foundation for international radiation protection assessments.
In this collaborative study, QST used the PARMA model to perform detailed calculations of cosmic-ray doses in living environments around the world, and, by combining the results with population distribution data, produced a “global map of cosmic-ray exposure doses” that more accurately reflects the actual conditions in each country and region. As a result, the global average annual effective dose from cosmic rays was revised downward from the previous estimate of 0.38 mSv/year to 0.30 mSv/year.
This achievement makes a major contribution to improving the reliability of public exposure assessments for natural radiation. It is also expected to find applications in a wide range of fields, including exposure management for aircraft crew and radiation protection in commercial space activities. The Nuclear Science and Engineering Center will continue to contribute to the realization of a safe and secure society based on scientific evidence through the development of advanced radiation analysis technologies.
URL of PARMA/EXPACS website https://phits.jaea.go.jp/expacs
JAEA HP Press release (Japanese only)
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)
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)
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