γ-spectroscopy and development of high resolution detectors in space and energy

The contribution of TUM and IKP to the joint research project is the development and construction of a mobile Compton camera which can be used to trace radioactive materials.

A mobile detector system consisting of a segmented large volume high purity germanium and a highly segmented planar silicon detector is developed for tracing radioactive sources using the method of Compton imaging. Weak radioactive sources can be localized and radioactive waste can be characterized by this system.

The energy and the direction of the incoming photon can be computed by measuring the spot of Compton scattering and photo absorption in combination with measuring the energy of the Compton electron and scattered photon (see figure 1). The precise reconstruction of the point of Compton scattering is possible in highly segmented planar silicon detectors. A segmented large volume position sensitive germanium detector (see figure 2) is able to measure precisely  the spot of photo absorption. The determination of the interaction point is possible because of a recently developed pulse shape analysis which compares the digitised preamplifier signals with simulated pulse forms using intelligent and fast algorithms (particle swarm optimisation). 

The scattering angle can be calculated from the Compton scattering formula:

\cos\theta = 1 - \frac{E_e m_e c^2}{E_{\gamma'}(E_{\gamma'}+E_e)}

If θ and the interaction points are known, the position of the source can be localized to the surface of a cone. The exact position can be computed from several measurements.

 

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