The COMPTEL gamma-ray telescope has been operating in low Earthorbit for six years, since the launch of the Compton Gamma-RayObservatory in April 1991. Comparisons of data for different orbits andepochs show evidence of activation on time scales from minutes (27Mg, τ1/2=9.5 min) to years (22Na, τ1/2=2.58 yr). The activation is correlated with both theorbital altitude and solar cosmic-ray modulation. Because it requirescoincident measurements in two different detectors, COMPTEL is mostsusceptible to instrumental background events in which two or morephotons are produced simultaneously
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