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The increase of Computed Tomography (CT) as an applicable metrology and Non Destructive Testing (NDT) method raises interest on developing the application fields to larger objects, which were rarely used in the past due to their requirements on the imaging system. Especially the classical X-ray generation techniques based on standard equipment restricted the applications of CT to typical material penetration lengths of only a few cm of steel. Even with accelerator technology that offers a suitable way to overcome these restrictions just the 2D radioscopy technique found a widespread application. Beside the production and detection of photons in the MeV range itself, the achievable image quality is limited using standard detectors due to the dominating absorption effect of Compton Scattering at high energies. Especially for CT reconstruction purposes these effects have to be considered on the development path from 2D to 3D imaging. Most High Energy CT applications are therefore based on line detectors shielding scattered radiation to a maximum with an increase in imaging quality but with time consuming large volume scan capabilities. In this contribution we present the High-Energy X-ray Imaging project at the Fraunhofer Development Centre for X-ray Technology with the characterization and the potential of the CT-system according to metrological and other application capabilities. [ABSTRACT FROM AUTHOR]

The COMPTEL and EGRET detectors aboard the Compton Gamma-Ray Observatory measured an extragalactic γ-ray background (EGRB) extending from ∼ 1 MeV to ∼ 100 GeV. Calculations performed making reasonable assumptions indicate that blazars can account for the background between ∼ l0 MeV and ∼ 10 GeV. Below 30 MeV, the background flux and spectrum are not very well determined and a dedicated satellite detector will be required to remedy this situation. Below 10 MeV, supernovae and possibly AGN may contribute to the extragalactic background flux. Above 10 GeV, the role of blazars in contributing to the background is unclear because we do not have data on their spectra at these energies and because theoretical models predict that many of them will have spectra which should cut off in this energy range. At these higher energies, a new component, perhaps from topological defects, may contribute to the background, as well as X-ray selected BL Lac objects. GLAST should provide important data on the emission of extragalactic sources above 10 GeV and help resolve this issue. GLAST may also be able to detect the signature of intergalactic absorption by pair production interactions of background γ-rays of energy above ∼ 20 GeV with starlight photons, this signature being a steepening of the background spectrum. [ABSTRACT FROM AUTHOR]