Temporal evolution of the intensities for different background lines. Left column, from top to bottom: the evolution of the 198 keV line measuring neutron irradiation, the 511 keV line from local positron annihilation, and the neutron capture line at 2.2 MeV. Right column, from top to bottom: the 1107 keV line from 69Ge activation, the 1764 keV line from 214Bi in the veto system, and the 1332 keV line from 60Co radioactivity as it builds up. Intensities are scaled to underlying continuum intensity. For comparison, the time history of the sunspot number count is shown. Failures of individual Ge detectors occurred at times marked by dotted vertical lines, and show the most significant impact in the case of the 511 keV line (see text).
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