Shaping neutron energies to achieve sensitivity and uniformity of bulk material analysis

摘要

In a bulk material analyzer in which bulk material (38) is received in an activation region (34) between a pair of neutron sources (14) laterally disposed on one side of the activation region for emitting neutrons for bombarding the bulk material within the activation region to cause gamma-rays to be emitted from the bombarded bulk material and a pair of gamma-ray detectors (16) laterally disposed on an opposite side of the activation region for detecting gamma-rays emitted from the bulk material, and in which a neutron moderator (20) is disposed between the neutron sources and the activation region for reducing the velocity of the emitted neutrons such that the neutrons entering the activation region include thermal neutrons and faster neutrons, the uniformity of sensitivity of the bulk material analyzer to materials at different positions in a sample of the bulk material being analyzed is enhanced by controlling the proportions of thermal neutron at different positions within the sample being analyzed. A neutron absorber (23) disposed close to the one side of the activation region reduces the proportion of thermal neutrons that enter the activation region from the one side of the activation region. A neutron reflector (25) disposed on the opposite side of the activation region at least as close to the activation region as the gamma-ray detectors reflects neutrons into the activation region for bombarding bulk material within the activation region. In some embodiments, the neutron absorber and/or the neutron reflector are adjustable; and the disposition of the neutron sources also is adjustable for also adjusting the proportion of the thermal neutrons that enter the activation region from the one side of the activation region. IMAGE