Abstract: The present invention provides a nuclear activation apparatus for one or more fluid samples comprising the following modules; a means for introducing one or more fluid samples to a sample conduit, an activation thimble, comprising a section of sample conduit configured for multiple passes adjacent a radiation source, an absorber located adjacent to the activation thimble, and a detector located adjacent the sample conduit, wherein the relative arrangement of the modules can be altered specific to an application and the rate of flow of the fluid sample adjacent the radiation source can be controlled.