In March 2012, the Double Chooz reactor neutrino experiment published its most precise result so far: sin22θ13 = 0.109 ± 0.030(stat.) ± 0.025(syst.). The statistical significance is 99.9% away from the no-oscillation hypothesis. The systematic uncertainties from background and detection efficiency are smaller than the first publication of the Double Chooz experiment. The neutron detection efficiency, one of the biggest contributions in detection systematic uncertainties, is the first part of my talk. 252Cf is used to determine the neutron detection efficiency in this study. The neutron detection efficiency from the 252Cf result is confirmed by the electron antineutrino data and Monte Carlo simulations. The seasonal variation in detector performance and the seasonal variations of the muon intensity are described in the second part of my talk. The detector stability is confirmed by observation of two phenomena: 1) the electron antineutrino rate, which is seen to be uncorrelated with the liquid scintillator temperature, and 2) the daily muon rate, which has the expected correspondence with the effective atmospheric temperature. The correlation between the muon rate and effective atmospheric temperature is further analyzed to determine the ratio of kaon to pion in the local atmosphere. Finally, the talk concludes with the potential instabilities from neutron detection efficiency and seasonal variation and estimation of how these potential instabilities affect the result of sin22θ13.