COMPTEL measurements of 1.809 MeV gamma-ray line emission from the Galactic plane

The COMPTEL experiment on the Compton Gamma‐Ray Observatory (CGRO) is designed to image celestial gamma radiation in the energy range from 0.75 to 30 MeV within a field of view of 1 steradian. It can locate strong point sources with an accuracy better than 1° and is capable of mapping diffuse emission at the same time. The Galactic plane was observed by CGRO for several periods in 1991 and 1992. Emission in the 1.8 MeV line (attributed to radioactive 26Al) along the Galactic disc is observed towards the Galactic center region. In addition, the observations away from the central region of the Galaxy reveal evidence for 1.8 MeV emission. These preliminary results provide new data for determination of the 26Al source origin: detailed mapping in the Galactic‐center region may be supplemented by study of other less distant nucleosynthesis regions, such as the Vela region and Carina arm.