[en] One of the most interesting questions concerns the nature of the weakly active nucleus of the Galaxy. Gamma spectroscopy contributes an important share to clarify the problem. Beside the measurement of the 0.511 MeV line arising from positron annihilation from the galactic center, a 1.81 MeV line was found, stemming from the decay of Al²⁶ and subsequent formation of Mg²⁶. A scenario for the processes going on in the galactic center is outlined. (UPO)

No abstract available

[en] A sky map of the anticenter region of the galaxy between α = 50deg to 110deg and delta = +10deg to +50deg at energies from 1-10 MeV is derived from data obtained during a balloon flight of the MPI Compton telescope. The telescope has a field of view of 40deg to 50deg (FWHM) and a 1σ-angular resolution of 5deg within its field of view. A significantly enhanced γ-ray emission is observed along the galactic plane from about l = 160deg to l = 195deg. Part of the emission is due to the Crab which can be resolved. The limited angular resolution of the telescope does not allow to decide whether the remainder of the emission is diffuse in nature or due to unresolved sources. No enhanced γ-ray emission is observed from the direction of the high energy γ-ray source Geminga (2CG 195+04)

[en] An image of the anticenter region of the Galaxy between right ascension 50⁰ and 110⁰ and between declination +10⁰ and +50⁰ in the energy range 1.1--10 MeV is derived from data obtained during a balloon flight with the MPI Compton telescope. The telescope has a field of view of 40⁰--50⁰ (FWHM) and a 1 sigma angular resolution of about 4⁰ within this field. A significantly enhanced γ-ray emission is observed along the galactic plane from l/sup II/ = 160⁰ to l/sup II/ = 197⁰. Part of the emission is due to the Crab Nebula. The energy spectrum of the pulsed and total Crab emission is determined. Because of the limited angular resolution of the telescope it is not possible to decide whether the remainder of the emission is diffuse in nature or due to unresolved sources. No significantly enhanced γ-ray emission is observed from the direction of the high-energy γ-ray source Geminga (2CG 195+04) or from the Seyfert galaxy MCG 8--11--11, which recently was reported to be a soft γ-ray source. An upper limit to the diffuse galactic γ-ray emission is determined, which leads to restrictions of the spectrum of interstellar cosmic ray electrons at MeV energies

[en] A simple model is developed in order to interpret the recently measured zenith angle distribution of MeV γ rays in the upper atmosphere, which shows a maximum of intensity at angles around 120degree (upward moving direction). Because γ ray production by electron bremsstrahlung is by far the most important process in this energy range, an attempt has been made to derive the γ ray source functions within the atmosphere from measured electron fluxes. The transport of γ rays from their source position to the detector altitude is simulated in a Monte Carlo calculation. The calculation shows that the observed maximum around zenith angles of 120degree is caused by those γ rays which were originally ejected preferentially in the horizontal direction but which were Compton-scattered on their way to the detector. Because the mean Compton scattering angle and the scattering probability depend on energy, the maximum in the zenith angle distribution varies with energy: with increasing energy it is more and more shifted toward 90degree

[en] An experimental calibration procedure for arbitrarily shaped liquid organic scintillation detectors is described, which is based on a coincidence arrangement using an NaI detector. (orig.)

[en] A simple model is developed in order to interpret the recently measured zenith angle distribution of MeV γ-rays in the upper atmosphere, which shows a maximum of intensity at angles around 120⁰ (upward moving direction). Because γ-ray production by electron bremsstrahlung is by far the most important process in this energy range, an attempt has been made to derive the γ-ray source functions within the atmosphere from measured electron fluxes. The transport of γ-rays from their source position to the detector altitude is simulated in a Monte Carlo calculation. The calculation shows that the observed maximum around zenith angles of 120⁰ is caused by those γ-rays, which were originally ejected preferentially in the horizontal direction, but which were Compton-scattered on their way to the detector. Because the mean Compton scattering angle and the scattering probability depend on energy, the maximum in the zenith angle distribution varies with energy: with increasing energy it is more and more shifted towards 90⁰