Activation in the COMPTEL double-scattering gamma-ray telescope

The COMPTEL gamma-ray telescope has been operating in low Earth orbit for six years, since the launch of the Compton Gamma-Ray Observatory in April 1991. Comparisons of data for different orbits and epochs show evidence of activation on time scales from minutes (/sup 27/Mg, /spl tau//sub 1/2/=9.5 min) to years (/sup 22/Na, /spl tau//sub 1/2/=2.58 yr). The activation is correlated with both the orbital altitude and solar cosmic-ray modulation. Because it requires coincident measurements in two different detectors, COMPTEL is most susceptible to instrumental background events in which two or more photons are produced simultaneously.