Evaluation of a Multilayer Neutron Detector for Nonproliferation and Arms Control

Current efforts are being made in the U.S. and Russia to determine appropriate schemes for the transparent monitoring of the storage of U.S. and Russian fissile weapons components. The results of experimental measurements using a multilayer neutron detector scheme are presented here. The measurements are used to evaluate the ability of the detector to produce unique signatures of fissile material components. The signatures from the detector must also be difficult or unfeasible to simulate. Therefore, the measurement environment (room background, relative positions of object and detector, and nearby objects) must be well controlled. In addition, the signatures should not reveal sensitive information about the design of the component. The neutron detector consists of five blocks of ten 3He tubes. Each block is separated by a layer of polyethylene to moderate incident neutrons. In addition, each layer is a separate data channel in the pulse counting system. The multilayer geometry and pulse counter provides energy spectral information for the incident neutrons in a five-channel histogram. In a verification application, a container is measured to produce a histogram, which is then compared to a template histogram of the expected object. A match with the template histogram in magnitude and shape confirms the presence of the object. This work was performed under the auspices of the U. S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under Contract No. W-7405-Eng-48.