Investigation of Nuclear Materials with Positron Measurements

Licentiate thesis, 2011

Positron Annihilation Lifetime Spectroscopy can be used to characterize radia- tion-induced material defects to subsequently optimize nuclear materials with respect to radiation damage. Nuclear Systems of the future such as Generation IV and fusion concepts demand high performance from structural materials, comprising a material's stability in highly-radiative and hot environments. Analyzing experimental data obtained with the Chalmers Pulsed Positron Beam can help to design material compositions that are able to perform safely under such such conditions. The following work summarizes the efforts made to understand necessary basics of the measurement technique and to validate simulation tools for estimating positron behavior in solid media. A study on positron depth profiling aims at approximating the range positrons travel until annihilation takes place in order to estimate the depth of ion-implanted defects. In the framework of the European collaboration project GETMAT, ions are used to simulate neutron irradiation as expected from reactor conditions in Generation IV Systems. Temporary results from this project are presented and lay base for more detailed information on the evolution of ion-implanted lattice defects. So far it is concluded that the Monte Carlo code PENELOPE is a useful tool for calibrating the Chalmers Pulsed Positron Beam since experimental and simulation data agree well with each other. Early results within GETMAT predict that microscopic material structures are clearly influenced by radiation even though distinct conclusions regarding macroscopic effects are not made yet.