Nuclear operations with reactors and particle accelerators lead to the generation of neutrons, with a consequent activation of surrounding shielding materials. In general these materials consist of a concrete bioshield with associated metal work from steel reinforcement and support structures. This paper considers the interaction mechanisms of the neutrons in the concrete and the distribution and activity profile of activated materials. The most common source of high thermal neutron fluxes is of course from fission reactor systems. However, there are also other systems such as fusion reactors, which generate a far higher energy neutron flux, as the requirement for electrical confinement of the plasma means that the available bioshielding close to the power source is more limited. In addition, there are also neutron generation mechanisms from particle accelerator systems such synchrotrons and Van De Graaf devices. This study examines the interaction mechanisms of the neutrons in the bioshields, the radioelement abundances of the activated products generated, in-situ and ex-situ measurement of their concentration and profile of the radionuclides and finally methods of assaying and sentencing such materials. Examples of decommissioning operations of reactor and accelerator systems will be given as practical examples of the use of the assaying methodologies developed.

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