Calibration of the mega prototype

Calibration measurements of the MEGA (Medium Energy Gamma-ray Astronomy) prototype have been performed with radioactive lab sources and at the High Intensity Gamma-ray Source (HIGS) at the Free Electron Laser Laboratory (FELL) of Duke University, Durham, NC. MEGA is a combined Compton scatter and pair creation telescope. It consists of two main detector units, the tracker and the calorimeter. Doublesided Silicon strip detectors form the tracker, which is surrounded by the pixelated CsI(Tl) blocks of the calorimeter. A prerequisite for successful data analysis is a calibration of each individual readout channel. This work is still ongoing. The performance of the detector units will be therefore presented as currently known. The encountered problems and the resulting (single detector) calibration methods will be described briefly. Since we aim at an energy range of 0.3 - 50 MeV, the HIGS -a Compton back-scattering source -with beams of mono-energetic, fully linearly polarized photons in the range of 0.7 - 50 MeV was a good match for the MEGA calibration. Measurements at various energies and for different incidence angles have been performed. Some preliminary results will be presented.