Photo-nuclear Reactions of Light Nuclei Studied by Proton Scattering at RCNP

by Tamii Atsushi (Research Center for Nuclear Physics)


Photo-nuclear reactions in the mass region below a mass of 60 will be systematically investigated in the project PANDORA (Photo-Absorption of Nuclei and Decay Observation for Reactions in Astrophysics).


Virtual photon excitation by proton scattering and a high-intensity real-photon beam by laser Compton scattering will be applied to excite target nuclei for measuring the photo-absorption cross-sections and the decay branching ratios covering the giant dipole resonance (GDR).

The primary motivation of the project is to determine the energy loss process of the nuclei consisting of the Ultra-high-energy cosmic rays (UHECRs) in the inter-galactic propagation. UHECRs are observed on earth up to above 1020 eV at the Pierre Auger and Telescope Array observatories. The origin and the acceleration mechanism remain a mystery. A recent analysis of the air-shower depth distribution showed a trend to be larger in mass between a proton and an iron at the highest energy. UHECR nuclei are predicted to lose their energy primarily by emitting particles after photo-nuclear excitation by absorbing a cosmic microwave background (CMB) photon. Thus, photo-absorption cross-sections and decay branching ratios are the keys for understanding the energy and mass evolution of UHECRs during the inter-galactic propagation.


The first experiment was carried out at RCNP in October 2023.


I will introduce the experimental method using the virtual photon excitation at RCNP and the status of the experiment.