Interacting loops: temporal evolution of final energy spectra of electrons (panel a) and protons (panel b), initiated at different snapshots during MHD experiment (where the fragmentation of one flux tube destabilises a second tube). An initial energy spectrum is seen as a dashed histogram, while the coloured spectra represent the final energies for orbits started at different times. A power law has been fit to each spectra between 100 eV and 1 MeV, with the power law index (p) and initiation time of each spectra given in the legend.