Energy resolution vs. energy. Shown are the line widths (FWHM) for the strongest single/isolated backgroundlines. The energy resolution functions are shown as obtained from pre-launch calibrations Attié et al. (2003, dashed line), and from mission data (solid line). Results obtained for different detectors are slightly offset in energy for better visibility, and are centred around the laboratory energy of the respective background line. The 511 keV line clearly presents an anomaly, and the 1107 keV line from ⁶⁹Ge may also beblended with contributions from nearby lines (see text).