For understanding an anomalous nuclear effect experimentally observed for the beryllium-9 nucleus at the Thomas Jefferson National Accelerator Facility, clustering aspects are studied in structure functions of deep inelastic lepton-nucleus scattering by using momentum distributions calculated in antisymmetrized (or fermionic) molecular dynamics (AMD) and also in a simple shell model for comparison. According to AMD, the ${}^9\mathrm{Be}$ nucleus consists of two $\alpha$-like clusters with a surrounding neutron. The clustering produces high-momentum components in nuclear wave functions, which affects nuclear modifications of the structure functions. We investigated whether clustering features could appear in the structure function $F_2$ of ${}^9\mathrm{Be}$ along with studies for other light nuclei. We found that nuclear modifications of $F_2$ are similar in both AMD and shell models within our simple convolution description although there are slight differences in ${}^9\mathrm{Be}$. It indicates that the anomalous ${}^9\mathrm{Be}$ result should be explained by a different mechanism from the nuclear binding and Fermi motion. If nuclear-modification slopes $d(F_2^A/F_2^D)/\mathit{dx}$ are shown by the maximum local densities, the ${}^9\mathrm{Be}$ anomaly can be explained by the AMD picture, namely by the clustering structure, whereas it certainly cannot be described in the simple shell model. This fact suggests that the large nuclear modification in ${}^9\mathrm{Be}$ should be explained by large densities in the clusters. For example, internal nucleon structure could be modified in the high-density clusters. The clustering aspect of nuclear structure functions is an unexplored topic which is interesting for future investigations.

• Received 7 August 2010

DOI:https://doi.org/10.1103/PhysRevC.83.035202