Spectral decomposition into lines, near the positron annihilation line at 511 keV (above), and the ²⁶Al line (below). The annihilation line itself requires a composite model of a narrow (instrumental width) and a broader component, representing different modes of β-decay in spacecraft or detector materials. Several low-intensity lines at nearby energies are part of the spectral model, all modelled as Gaussians (red dashed lines). The isotopes causing these various background lines are indicated when identified.