Abstract: The invention refers to a device for determining the nuclide content of a radioactive fluid. The device comprises a space (2) for receiving the fluid, a primary detector (6) for detection of gamma radiation emitted form the fluid in the space (2), and a processing member (10) for determining the nuclide content of the fluid based on the detected gamma radiation. The primary detector (6) includes a first detector part (8) having a front end directed towards the space and a second detector part (9) arranged adjacent to said front end between the first detector part (8) and the space (2).