In a groundbreaking advancement poised to reshape nuclear physics and astrophysics, researchers at the Shanghai Synchrotron Radiation Facility (SSRF) have successfully conducted high-precision measurements of the ^27Al(γ, n)^26Al reaction using quasi-monoenergetic gamma-ray beams. This significant achievement addresses decades-old inconsistencies in nuclear cross-section data that have long challenged scientists studying nucleosynthesis and cosmic phenomena. Leveraging the unique capabilities of the SLEGS beamline—powered by state-of-the-art inverse Compton scattering technology—the research team produced remarkably uniform and finely tunable gamma-ray energies, thereby enabling systematic and reliable exploration of nuclear reaction mechanisms critical to astrophysical models.
The ^27Al(γ, n)^26Al reaction is intimately linked with stellar nucleosynthesis, playing a crucial role in the formation of radioactive aluminum-26 within stars and supernovae. Aluminum-26 serves as a cosmic chronometer and energy source, its decay gamma emissions providing invaluable insights into astrophysical processes and the chemical evolution of the universe. Despite the reaction’s importance, previous experimental efforts struggled with large discrepancies, often up to 50%, due to limitations inherent in traditional gamma-ray sources such as bremsstrahlung and positron annihilation radiation. These conventional methods suffered from broad energy spectra and high systematic uncertainties, resulting in conflicting datasets that impeded theoretical advancements.
Capitalizing on SLEGS’s advanced laser Compton scattering (LCS) gamma-ray beams, researchers achieved an unprecedented level of precision by mapping the reaction cross sections across 38 discrete energy points ranging from 13.2 to 21.7 MeV. The use of LCS provides several critical advantages—most notably, the generation of quasi-monochromatic gamma rays with a remarkably narrow energy spread and the ability to finely tune energies with 10 keV resolution steps. This precision tuning is critical in isolating specific nuclear reaction channels and minimizing background interference, enabling direct and accurate measurements that surpass those of previous studies.
Central to the success of this study is the innovative deployment of a novel ^3He flat-efficiency detector (FED). The design incorporates concentric neutron counters embedded within polyethylene moderators, optimized to maintain a uniform and flat neutron detection efficiency between 40 and 42% across a broad neutron energy spectrum. This uniformity dramatically minimizes systematic biases that have traditionally confounded neutron detection in nuclear reaction experiments. Complemented by sophisticated pulse processing techniques, the FED delivers clear and unambiguous neutron signals, enhancing the reliability of the recorded data. The detector’s performance was rigorously benchmarked using Geant4 Monte Carlo simulations and meticulously calibrated against standardized ^252Cf neutron sources, confirming accuracy levels to within a remarkable 1.3%.
The resulting dataset shows compelling agreement with the latest global nuclear data evaluations, particularly the TENDL-2021 library, with improved smoothness and consistency across the energy domain below 16.3 MeV. Notably, the experimental results identify significant deviations from previously accepted data above this threshold, where older datasets exhibited unphysical oscillations that posed challenges for theoretical nuclear modelers. This refined dataset enables enhanced parameterization of nuclear reactions within the framework of quasiparticle random phase approximation (QRPA) models, which are pivotal for simulating the production rates and behavior of ^26Al in astrophysical environments, including supernova explosions and the interiors of massive stars.
This research not only fulfills a critical need in nuclear data evaluation but also substantially strengthens the foundation upon which many astrophysical simulations rest. The improved cross-section measurements allow for more accurate modeling of nucleosynthetic pathways, leading to a deeper understanding of galactic chemical evolution and radioactive isotope distribution in space. Furthermore, the enhanced reliability of nuclear reaction data influences a broad array of applications ranging from nuclear energy safety protocols to the precision manufacture of medical isotopes, where knowledge of photonuclear processes is essential.
The SLEGS facility’s ability to deliver finely tunable gamma rays with exceptional beam quality exemplifies China’s rising prominence in photonuclear experimental research. The top-up operational mode of the SSRF storage ring, maintaining a critically stable electron beam current between 160 and 210 mA at energies of 3.5 GeV, underpins the consistent production of quasi-monoenergetic gamma rays via inverse Compton scattering with a 10,640 nm CO₂ laser. This orchestration of laser and electron beams represents a technical tour de force, facilitating experimental regimes previously unattainable with conventional photon sources.
Future research ambitions include extending these precise measurements to explore the ^27Al(γ, 2n) reaction channel, which remains underexplored yet carries significant implications for modeling nuclear reaction networks in astrophysical events. The team’s continued innovation in detector design and experimental technique promises to unlock new frontiers in nuclear science, bridging gaps between fundamental nuclear physics, applied technologies, and cosmological inquiry.
Moreover, SLEGS’s advancements resonate well beyond astrophysics. The facility’s breakthroughs contribute to a safer and more efficient nuclear energy landscape by informing reactor design and neutron behavior under photon irradiation. In medical sciences, photonuclear reactions underpin the generation of novel isotopes used in diagnostic imaging and targeted therapies, highlighting the interdisciplinary impact of this research. As the global scientific community increasingly demands high-integrity nuclear datasets, the refined photonuclear measurements at SLEGS position China at the forefront of delivering transformative solutions across sectors.
Dr. Pu Jiao and the dedicated team led by Professor Chunwang Ma at Henan Normal University and the Henan Academy of Sciences have pushed the envelope of experimental nuclear science with this work. Their blend of precision engineering, comprehensive simulation validation, and methodical calibration protocols exemplify the meticulous approach required for high-stakes nuclear measurements. Sustained support from national scientific funding bodies underscores the critical importance of these efforts in maintaining and expanding China’s strategic capabilities in nuclear research and technology development.
By resolving previously entrenched experimental uncertainties and aligning nuclear cross-section data more closely with theoretical constructs such as QRPA, this work sets a new standard for nuclear data quality and reliability. The enhanced agreement between empirical data and model predictions fosters confidence in simulations that inform not only astrophysical theories but also diverse fields dependent on accurate nuclear reaction mechanisms. The collaborative integration of laser technology, particle physics, detector innovation, and computational modeling encapsulates a holistic scientific approach that is emblematic of next-generation nuclear research.
The detailed and highly reproducible nature of these findings offers a compelling template for future investigations into photon-induced nuclear reactions. The unprecedented measurement accuracy achieved reinstates confidence in archival nuclear databases while encouraging the reevaluation of older datasets, potentially reshaping long-held assumptions in nuclear science. This contribution exemplifies the powerful synergy of advanced instrumentation and theoretical insight, marking a transformative milestone in the pursuit of understanding the intricate behaviors governing atomic nuclei and their cosmic manifestations.
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Subject of Research: Not applicable
Article Title: Measurements of ^27Al(γ, n) reaction using quasi‑monoenergetic gamma beams from 13.2 to 21.7 MeV at SLEGS
News Publication Date: 25-Feb-2025
Web References:
http://dx.doi.org/10.1007/s41365-025-01662-y
Image Credits: Chun-Wang Ma
Keywords
Nuclear reactions, Nuclear physics, Nuclear reaction theory, Nuclear fusion
