Evaluation of Photo-Disintegration Cross-Section for Light Nuclei Using SRC Based Approach

The SRC presence in nuclei has been confirmed with a wide variety of probes which include photons, pions, and multi-GeV electron and proton beams. These observations have stimulated a range of phenomenological/theoretical models including Quasi-Deuteron Model (QDM), the Independent Pair Model (IPAM), the 2N interaction model for pion interaction, and a recently proposed contact formalism. The required SRC percentile inside nuclei varies for different probes. In QDM for N=Z nuclei, it is about 50% of all nucleons (=NZ/A) and it accounts, as high as, 70% of pion absorption events (through 2N reaction mechanism). In this work, we propose an extension of IPAM in which the nucleons are assumed in 2-body/3-body SRCs instead of independently moving nucleons in mean-field. Apart from encompassing the above mentioned SRC observations, the current approach is also expected to provide an understanding of the cluster observations (since the paired n-p SRCs would be equivalent to quasi-alpha structures) and binding energy saturation (since the fundamental NN interaction in the SRC formation remains the same) in nuclei. Here, we have employed this approach to calculate the total photo-disintegration cross-section of N=Z light nuclei for Eγ ranging from 10 to 140 MeV. The photodisintegration process is assumed to be due to the quasi-deuteron/np-SRC and quasi-alpha degree of freedom. The photo-disintegration cross-section of quasi-deuterons/np-SRCs is evaluated by scaling the well-known expressions for free deuterons while that of quasi-alpha structures is estimated by Gunn-Irving photo-disintegration formulation. A significant fraction of the photo-disintegration cross-section in the GDR region may be accounted for by the contribution of quasi-α degree of freedom which decreases with higher Eγ. The derivation of the Levinger formula is obtained without any additional assumptions. The present work suggests an alternative and viable description of photodisintegration for N=Z nuclei.