Characterization of neutron stray fields for residual activation estimation around high-energy accelerators using spectrometric and Monte Carlo methods

Information about the neutron spectral energy distribution is useful for various purposes, in particular for radiation protection and dosimetry or for the determination of residual neutron-induced radioactivity in shielding materials of high-energy accelerators.
A suitable device for spectrometric measurements of neutron fields is the extended range Bonner Sphere spectrometer (ERBSS). During this work, an ERBSS manufactured in Paul Scherrer Institute (PSI) was characterized and calibrated. Furthermore, state of the art measurement and data evaluation techniques based on Bayesian methods were adapted and optimized for the application in specific fields. The neutron spectrum was measured with the ERBSS around the PSI high-intensity proton accelerator (HIPA). Results of these measurements were compared with results obtained by the Monte Carlo particle transport code (MCNP) to benchmark the models used for investigation of neutron radiation field properties and residual activation. For the application in a multi-source environment, the background subtraction method was developed. This method is based on the application of shadow object, Monte Carlo simulations and Bayesian data analysis. It was tested by measurements in a workplace field produced by the spent nuclear transport and storage cask in the interim storage (Zwilag).