  INTEGRAL/SPI is a space-based coded mask telescope featuring a 19-element
Germanium detector array for high-resolution gamma-ray spectroscopy,
encapsulated in a scintillation detector assembly that provide a veto for
background from charged particles. In space, cosmic rays irradiate spacecraft
and instrument, which results in a large instrumental background from
activation of those materials, and leads to deterioration of the charge
collection properties of the Ge detectors. We use 13.5 years of INTEGRAL/SPI
spectra for each detector and for each pointing of the satellite. Spectral fits
provide us with details about separated background components. From the
strongest background lines, we first determine how the spectral response
changes with time. We then determine how the instrumental background components
change in intensities and other characteristics, most-importantly their
relative distribution among detectors. Spectral resolution of Ge detectors in
space degrades with time, up to 15% within half a year, consistently for all
detectors, and across the SPI energy range. Semi-annual annealing operations
recover these losses, yet there is a small long-term degradation. The intensity
of instrumental background varies anti-correlated to solar activity, in
general. There are significant differences among different lines and with
respect to continuum. Background lines are found to have a characteristic,
well-defined and long-term consistent intensity ratio among detectors. We use
this to categorise lines in groups of similar behaviour. The dataset of
spectral-response and background parameters as fitted across the INTEGRAL
mission allows studies of SPI spectral response and background behaviour in a
broad perspective, and efficiently supports precision modelling of instrumental
background.
