MEASURING CONCENTRATIONS OF ELEMENTS USING NEUTRON RADIATION

The invention provides an apparatus for measuring the concentrations of elements in a material sample by the capture gamma method, said apparatus including a neutron source in the form of an isotope source or a neutron generator, a moderator surrounding the neutron source and being at least partly constituted by heavy water, a semiconductor detector serving as gamma radiation detector and positioned in the immediate vicinity of the material to be analyzed and in the flux of slow neutrons, so much of the moderator being provided before the detector that this is reached only by a very low number of fast neutrons that have a damaging effect upon the detector. The material itself can form part of the moderator and also graphite is preferably used as a moderator around said heavy water. Furthermore, a body of bismuth having the shape of a cone or a double cone is preferably positioned in front of the neutron source so as to absorb gamma radiation and to scatter fast neutrons.