Evaluation of the activation of the radiation shielding of the LaDiff neutron triple-axis-spectrometer at FRM-II by simulation/calculation

Neutron radiation is widely used for investigation of matter at research reactors and spallation sources. One undesired side-effect is the production of radioactive nuclides in structure materials of the instruments (e.g. mounting structures and radiation shieldings) due to neutron capture reactions. Hence the structure materials themselves become radiation sources. The knowledge of the activities after a certain time of operation is essential for determination of the accessibility, for modifications of the instrument, for reusing the material and for waste management. It is desirable to have these data in the design phase of the instrument. One possibility to obtain the data is a combination of simulation and calculation. In this paper the simulations/calculations for the LaDiff cold triple-axis neutron spectrometer project at FRM-II (research reactor Munich) are presented. The activities in the shielding house around the experimental area of the instrument made from stainless steel and lead are considered for the cases with and without boron-carbide cover and for different Sb-contents of the lead layer. The influence of the skyshine is also considered.