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A diverse set of probes has confirmed two-nucleon (2N) short-ranged correlated structures inside nuclei, mainly in n-p form [1]. Additionally, some light nuclei of astrophysical importance, like $^7$Li and $^7$Be, exhibit clear signatures of loosely bound 3N structures with core-α [2]. Moreover, the energetic photons in GDR and quasi-deuteron regions are expected to interact with few-nucleon correlated structures and clusters present in light nuclei. Hence, the photonuclear reaction cross-section for light nuclei like $^6$Li, $^7$Li, $^7$Be, $^{12}$C, $^{15}$N, $^{16}$O etc., can be evaluated by summing the cross-sections of their constituent 2N, 3N correlated structures and clusters. After a detailed analysis of the photonuclear processes for deuteron, tritium, $^3$He, and $^4$He and assuming that the photonuclear cross-section of quasi-deuterons/quasi-tritium/quasi-$^{3}$He and $\alpha$-cluster can be evaluated by scaling the appropriate expression for their free counterparts, we have obtained the photonuclear reaction cross-sections for light nuclei [3-4]. A significant fraction of the GDR cross-section may be accounted for by the contribution of the quasi-$\alpha$ degree of freedom [3], which decreases for higher E$\gamma$. Contrary to general perception, the quasi-deuteron photonuclear contribution starts in the GDR region itself and dominates for E$\gamma$ > 50 MeV. The present work also illuminates the microscopic origin of the Levinger formula, the damping factor for the quasi-deuteron cross-section at lower Eγ values, and an explanation for the double peak excitation function for the $^6$Li photonuclear reaction [2], etc. Some of the testable predictions for the current approach are also outlined.
[1] R. Dalal and MacGregor I. J. D, “Nucleon-nucleon correlations inside atomic nuclei: synergies, observations and theoretical models,” https://doi.org/10.48550/arXiv.2210.06114
[2] M. R. Sené et al., “The 7Li(γ, N) and 7Li(e, N) reactions at intermediate photon energies,” Nucl. Phy. A, 442, 215 (1985).
[3] R. Dalal and R. Beniwal, “Photo-disintegration of N=Z light nuclei using SRC-based approach,” PoS (PANIC2021), 380, 323 (2021).
[4] R. Beniwal and R. Dalal, SRC based model for the photonuclear reactions on N=Z light nuclei, Accepted in Phy. At. Nucl. (2023).
