Neutronenaktivierungsanalyse mit gepulsten 14 MeV Neutronen zur Charakterisierung heterogener radioaktiver Abfälle

For the transport, interim storage and disposal of radioactive waste, it is assumed to have knowledge of the radioactive and non-radioactive inventory 1. In order to determine the radioactive inventory destructive (e.g. $\alpha$-, $\beta$-, $\gamma$-measurements according to wet chemical sample preparation) and non-destructive (e.g. $\gamma$-scanning and neutron measurements) measurement methods are used 2. For the characterization of non-radioactive substances a prototype 3 for the assay of small-volume (50 L) samples was constructed and parameterized using the neutron activation analysis (NAA) with a pulsed 14 MeV neutron source. Subsequently, the non-destructive analytical method called MEDINA (Multi Element Detection Based on Instrumental Neutron Activation) for 200 l waste drums was developed in a cooperation between RWTH Aachen University and Forschungszentrum Jülich GmbH $^{4 5}$. The aim of this thesis is to investigate and characterize heterogeneous mixed samples regarding their material composition as well as their inhomogeneous distribution. For this purposes, studies were carried out on 200 l steel drums with heterogeneous matrices using the NAA in the MEDINA facility. The samples are composed out of a mixture of concrete and polyethylene(PE) bodies. Due to its high hydrogen content, the PE can have a strong influence on the neutron moderation and neutron absorption and can thereby occur as a possible disturbance variable in the characterization of the non-radioactive inventory. For these studies a pulsed 14 MeV neutron source is used to record the prompt and delayed $\gamma}$-rays between the neutronpulses, separately. Thus, the performance of the MEDINA method relating to strongly moderating mixed matrices and their characterization is studied. [...