Gamma activation analysis (GAA) represents a powerful elemental analysis technique, particularly suitable for light elements and those insensitive to thermal neutron activation. The establishment of the Shanghai Laser Electron Gamma Source (SLEGS) beamline has provided a unique platform in China for conducting advanced gamma activation studies using quasi-monochromatic gamma beams and obtaining high-precision nuclear data. This paper systematically presents the gamma activation data measurement methodology and experimental setup developed at the SLEGS beamline, while demonstrating its specific applications and significant achievements in beam diagnostics and nuclear astrophysics research. As is shown in the overall workflow in Fig. 10.
The study was conducted at the SLEGS beamline. SLEGS generates tunable quasi-monochromatic gamma beams in the energy range of 0.66–21.7 MeV through inverse Compton scattering mode between a 3.5 GeV electron beam and a 10.64 μm CO₂ laser (see experimental layout in Figure 1). The experimental procedure began with the online irradiation of target samples (e.g., natural abundance Au, Zn and Ru/Ga) to produce radioactive nuclei via photonuclear reactions. During irradiation, beam monitoring was conducted using LaBr₃(Ce) or BGO detectors alongside spectral unfolding. Subsequently, offline γ-ray spectroscopy was performed on the activated samples using shielded HPGe detectors. Based on these measurements, the reaction cross-sections were ultimately determined by analyzing characteristic gamma peaks in conjunction with beam parameters and detector effciency data.
Absolute calibration of SLEGS gamma beam intensity was successfully achieved using ¹⁹⁷Au(γ,n)¹⁹⁶Au and ⁶⁴Zn(γ,n)⁶³Zn reactions. The measured results agreed with online monitor data and Geant4 simulations within 10% uncertainty (Figure 6), validating activation as a reliable beam diagnostic tool. Key photonuclear reaction cross-sections relevant to p-process nucleosynthesis were measured. Using natural abundance Ru targets, preliminary quasi-monoenergetic cross-section data were obtained for ⁹⁶Ru(γ,n)⁹⁵Ru, ⁹⁶Ru(γ,p)⁹⁵Tc and ⁹⁸Ru(γ,n)⁹⁷Ru reactions (Figures 8a, 8b). Systematic measurements of the ⁶⁹Ga(γ,n)⁶⁸Ga monoenergetic reaction cross-section were performed (Figures 8c, 8d). The experimental data constrained parameters in the TALYS nuclear reaction model, enabling calculation of ⁶⁹Ga(γ,n), (γ,p), and (γ,α) reaction rates over 1.5~10 GK temperature range (Figure 9). REACLIB-format parameters were derived for astrophysical network calculations. These experimental results provide crucial constraints for understanding the origin of p-nuclei.
The study has successfully established a comprehensive and reliable gamma activation data acquisition and analysis platform at the SLEGS beamline of Shanghai Synchrotron Radiation Facility. Experimental results demonstrate that this platform can not only precisely calibrate gamma beam parameters but also conduct frontier fundamental research in nuclear astrophysics, particularly for measuring critical yet challenging p-process photonuclear reaction cross-sections. The obtained datasets hold significant importance for nuclear databases and astrophysical models. Looking forward, the SLEGS gamma activation platform will expand its applications to broader fields including characteristic nuclide identification, archaeometry, materials science, and medical isotope production.
Low-background gamma data and partial gamma activation data were provided, which can be accessed in the dataset at: https://www.scidb.cn/s/RVRjEz.