In a groundbreaking advancement in nuclear physics, researchers at the Institute of Modern Physics (IMP), Chinese Academy of Sciences, in collaboration with international experts, have successfully synthesized the isotope protactinium-210 for the first time. This newly-created isotope pushes the boundary of known matter by representing the most neutron-deficient form of protactinium ever observed. The discovery not only expands the nuclear landscape but also offers fresh insights into the fundamental behaviors of atomic nuclei that exist near the limits of nuclear stability. Details of this pioneering work were published on May 29, 2025, in the prestigious journal Nature Communications.
Atomic nuclei are intricate quantum many-body systems composed of protons and neutrons bound by nuclear forces. The synthesis and study of rare and exotic isotopes open doors to unraveling aspects of nuclear structure and dynamics that remain largely unexplored. The nuclear chart theoretically encompasses around 7,000 nuclides, but experimental evidence exists for only about 3,300, leaving a significant domain uncharted. Creating neutron-deficient isotopes, especially in the heavy actinide region, is exceptionally challenging due to their fleeting existence and the minuscule likelihood of production, often quantified by extremely low cross-section values.
The newly synthesized isotope protactinium-210 lies deep within the proton drip line, an area of the nuclear chart where nuclei have so many protons relative to neutrons that they are prone to spontaneous proton emission or alpha decay. Producing such isotopes requires precision and innovation. At the China Accelerator Facility for Superheavy Elements (CAFE2), researchers accelerated a calcium-40 ion beam to bombard a lutetium-175 target. The resulting fusion-evaporation reaction led to the creation of protactinium-210 nuclei. Despite the extremely low production cross-section of approximately seven picobarns—equating to a probability of only a few events among trillions of reactions—researchers observed 23 distinct decay events, a testament to the facility’s sensitivity and the experiment’s meticulous design.
Central to the success was the use of the gas-filled recoil separator known as the Spectrometer for Heavy Atoms and Nuclear Structure-2 (SHANS2). This state-of-the-art instrument allows for efficient separation and identification of the desired heavy isotopes from a plethora of reaction byproducts. The detection of alpha decay signals enabled precise characterization of protactinium-210’s decay properties, extending existing systematics within this proton-rich region. The experimental results showed remarkable alignment with theoretical nuclear models, especially shell model calculations that predict nuclear behavior near and beyond the proton drip line, underscoring the robustness of modern nuclear theory.
Alpha decay, an essential mode of radioactive decay for heavy proton-rich nuclei, involves the emission of an alpha particle (two protons and two neutrons) from the parent nucleus, transforming it into a different element. Measuring the half-life and decay energies of protactinium-210 provides critical benchmarks for nuclear models and helps refine our understanding of nuclear forces under extreme proton-to-neutron ratios. The extremely short half-lives on the order of milliseconds to microseconds further highlight the experimental challenges faced by the team and the necessity for advanced detection and data acquisition systems.
The ramifications of synthesizing protactinium-210 extend beyond the identification of a new isotope. This milestone demonstrates the capability of CAFE2 to explore the landscape of heavy and superheavy nuclei, paving the way for future experiments aiming to discover new elements with even higher proton numbers. The delicate balance between nuclear binding energy and repulsive forces governs the limits of nuclear existence, and pushing these boundaries informs both nuclear physics and astrophysical phenomena such as nucleosynthesis in explosive stellar environments.
This research also reflects the continuous evolution and globalization of nuclear physics, with collaborative efforts crossing institutional and geographical boundaries. In addition to IMP, partners from the University of Chinese Academy of Sciences, Advanced Energy Science and Technology Guangdong Laboratory, Shandong University, and other contributing institutions played critical roles. Such joint ventures enhance the pooling of expertise, resources, and technologies necessary for high-stakes experimental undertakings.
Given the extraordinarily low production cross-sections and ephemeral existence of isotopes like protactinium-210, each observed decay event represents an invaluable data point. The statistical accumulation of 23 decay events was achieved through persistent experimentation and demonstrates the precision of experimental apparatus and methodology. This precision is vital for establishing reliable decay chains and confirms the isotope’s identity beyond reasonable doubt, distinguishing protactinium-210 from neighboring or contaminant nuclei.
From a broader perspective, studies of rare isotopes in the neutron-deficient actinide region yield insights into the nuclear shell effects and shape coexistence phenomena at the limits of nuclear stability. Such knowledge enriches theoretical frameworks and enhances predictive capabilities about nuclei far from stability, which are often inaccessible via other experimental means. This information is instrumental for applications ranging from nuclear medicine to understanding fundamental interaction forces within matter.
The fusion-evaporation technique employed here exemplifies the sophisticated experimental approaches required in modern nuclear synthesis. Accelerating medium-mass ion beams—such as calcium-40—and bombarding heavier targets can occasionally create compound nuclei that subsequently evaporate neutrons and protons to form new isotopes. Fine-tuning beam energies, target thicknesses, and detector sensitivities is essential for maximizing yields and isolating rare reaction channels that generate exotic isotopes like protactinium-210.
Looking ahead, the capability to synthesize and study such proton-rich isotopes suggests promising avenues for charting the unknown territories of the nuclear landscape. By extending alpha-decay systematics, researchers can validate nuclear models at extreme proton-to-neutron ratios, which has implications for understanding forces within the nucleus and predicting properties of yet-undiscovered elements. These explorations contribute fundamentally to our understanding of matter and the overarching principles that govern nuclear stability and transformation.
In summary, the landmark discovery of protactinium-210 represents a significant leap in nuclear science, achieved through advanced experimental ingenuity and international collaboration. It highlights the ongoing quest to map uncharted nuclides, challenges theoretical nuclear physics to account for extreme cases, and solidifies the prowess of cutting-edge research facilities like CAFE2. As humanity continues to probe the atomic nucleus, milestones such as these pave the way to unravel deeper cosmic and subatomic mysteries.
Subject of Research: Not applicable
Article Title: Discovery of the α-emitting isotope 210Pa
News Publication Date: 29-May-2025
Web References:
https://doi.org/10.1038/s41467-025-60047-2
References:
Nature Communications, DOI: 10.1038/s41467-025-60047-2, May 29, 2025.
Image Credits: IMP
Keywords
Particle physics, Nuclear physics, Particle accelerators, Particle theory
