  We study the local vortex-vortex interaction force $\textbf{f}_i$ of the
structure frozen during a field-cooling process in an electron-irradiated
Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ sample. We compute this magnitude from
snapshots of the vortex structure obtained via magnetic decoration experiments
at various fields H in the same sample. Since the observed structures
correspond to the equilibrium ones frozen at T$\sim$T$_{irr}$(H), at this
temperature the local modulus of $\textbf{f}_i$ roughly equals the local
pinning force at the decorated surface of the sample. We estimate the most
probable local pinning force from the mode value of the f$_i$(r) distribution,
f $_{p}^{m}$. We found that f $_{p}^{m}$ grows algebraically with H and in
electron-irradiated samples is 50-20% smaller than for samples with columnar
defects.
