Absolute thermal neutron fluence determination by thin film of natural uranium

An absolute monitor of thermal neutron fluence based on the 235U induced fission was developed. This monitor is constituted by a solid state nuclear track detector juxtaposed to a natural uranium film with a negligible self-absorption to fission fragments. In order to perform the calibration of the films, the alpha-activity was measured by using nuclear emulsions. The preparation, calibration and employment procedures of this monitor are presented.