Abstract: A method and an apparatus are used for determining the neutron flux density of a neutron-emitting source, in particular a reactor core of a nuclear power facility. In the method, a first measurement signal and a second measurement signal, which differ from one another and are each monotonally dependent on the neutron flux density, are used to form a wide-range signal that depends uniquely on the neutron flux density. The wide-range signal is defined region-by-region, the wide-range signal is equated to the first measurement signal in a region where the values of the neutron flux density n are lower, n<n.sub.1, is equated to the second measurement signal in a region where the values of the neutron flux density are higher, n>n.sub.2, and is equated to a monotonal function of both measurement signals in an overlapping region located in between.