Obtaining uniformity of response in analytical measurement in a

Abstract

In an apparatus for neutron-capture-based on-line elemental analysis of bulk substances, an improved uniformity of response of analytical measurement will make the apparatus less sensitive to segregations that occur in moving streams of the bulk substance. The apparatus incorporates a measurement volume having a substantially-square cross-section with rounded corners in the plane perpendicular to the direction of flow in order to exclude the bulk substance from regions of unusual sensitivities and to facilitate the orientation of the instrument for minimum sensitivity to segregations in the bulk substance. The apparatus also includes a plurality of neutron sources which expose the analyzed bulk substance momentarily contained within the apparatus to a flux of neutrons. The apparatus also provides for the use of neutron reflectors to increase the neutron flux near the sides of the measurement volume, further improving the uniformity of measurement. The analyzed substance captures some of the neutrons by (n,.gamma.) reactions, producing prompt gamma rays which are detected to provide the composition measurement. The use of multiple sources causes the neutron flux to rise instead of fall near the sides of the volume containing the bulk substance compared to the center of the volume, and flux variations can be made to cancel solid-angle variations to produce a more-uniform response over a substantial portion of the measurement volume. Similarly the use of multiple gamma-ray detectors can also reduce these solid-angle variations, improving measurement uniformity, particularly if the measurement volume is large because of material-flow requirements.