Enhancement of measurement accuracy in bulk material analyzer

In a bulk material analyzer in which bulk material is received in an activation region between a pair of neutron sources 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 laterally disposed on another side of the activation region for detecting gamma-rays emitted from the bulk material, a primary neutron moderator is disposed about the neutron sources for reducing the velocity of the emitted neutrons; and a secondary neutron moderator is disposed about the primary neutron moderator for further reducing the velocity of the neutrons and is further disposed adjacent the lateral edges of the activation region for channeling and reflecting the neutrons into the activation region. The two gamma-ray detectors are disposed toward opposite lateral edges of the activation region, with each detector being skewed so that a portion of each detector that is closer to the edge of the activation region toward which the detector is disposed than to the lateral center of the activation region is disposed closer to a plane passing laterally through the center of the activation region than is another portion of each detector that is closer to the lateral center of the activation region than to the edge of the activation region toward which the detector is disposed. Spatial compensators are disposed adjacent the same side of the activation region as the detectors for reflecting neutrons toward the activation region at a greater density toward opposite lateral edges of the activation region than toward the center of the activation region. Bladders containing a liquid primary neutron moderating material that expands and contracts with temperature variations, such as heavy water, are tightly packed within a compartment for maintaining a substantial quantity of the liquid material between the neutron sources and the activation region notwithstanding thermal contraction of the liquid material; and a resilient compressible foam is disposed about the bladders for enabling the tight packing of the liquid material to be maintained notwithstanding expansion and contraction of the liquid material.