The Double Chooz experiment aims at accurately measuring the value of the ?13 leptonic mixing angle. To this intent, the experiment makes the most of two identical detectors – filled with gadolinium-loaded liquid scintillator – observing ? ?e’s released by the two 4.25 GWth nuclear reactors of the French Chooz power plant. The so-called "far detector" – located at an average distance of 1050m from the two nuclear cores – has been taking data since April 2011. The "near detector" – at an average distance of 400m from the cores – has monitored the reactor since December 2014. The ?13 mixing parameter leads to an energy dependent disappearance of ? ?e’s as they propagate from the nuclear cores to the detection sites, which allows for a fit of the sin2 2?13 value. By reason of correlations between the detectors and an iso-flux layout, the detection systematics and the ? ?e flux uncertainty impairing the ?13 measurement are dramatically suppressed. In consequence, the precision of the ?13 measurement is dominated by the uncertainty on the backgrounds and the relative normalisation of the ? ?e rates. The main background originates from the decay of ?n-emitters – generated by ?-spallation– within the detector itself. The energy spectra of these cosmogenic isotopes have been simulated and complemented by a diligent error treatment. These predictions have been successfully compared to the corresponding data spectra, extracted by means of an active veto, whose performance has been studied at both sites. The rate of cosmogenic background remaining within the observing ? ?e candidates has also been assessed. Additionally, the normalisation of the observing ? ?e e rates, bound to the number of target protons within each detector, has been evaluated. All this work was part of the first Double Chooz multi-detector results, yielding sin2(2?13) = 0.111 ± 0.018.