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ANS hosts webinar on criticality safety standards
A diagram depicting the NRC’s regulatory structure for nuclear criticality safety. (Image: Oak Ridge National Laboratory)
The American Nuclear Society’s Risk-informed, Performance-based Principles and Policy Committee (RP3C) held another presentation in its monthly Community of Practice (CoP) series last month. RP3C chair Steven Krahn opened the meeting with brief introductory remarks about the importance of risk-informed, performance based (RIPB) decision-making and the need for new approaches to nuclear design that go beyond conventional and deterministic methods.
John I. Martinez, Derek W. Schmidt, Thomas H. Day, Christopher Wilson, Valerie E. Fatherley
Fusion Science and Technology | Volume 73 | Number 3 | April 2018 | Pages 453-457
Technical Paper | doi.org/10.1080/15361055.2017.1406238
Articles are hosted by Taylor and Francis Online.
The neutron imaging pinhole is a complex aperture that is designed to have its image plane at the center of a laser fusion capsule implosion. The aperture’s high-Z materials of tungsten and gold block the neutrons so that only the neutrons passing through the machined apertures make it to the image plane and detector. The pinhole assembly consists of 11 layers of gold in between two layers of tungsten and gold. These 64 triangular pinholes and six penumbra apertures provide a matrix image that can be reconstructed to image complex deuterium-tritium neutron burn details in laser fusion capsules. The gold layers were diamond turned flat before the profiles were cut into their faces. Four of the layers were profiled with penumbral profile arrays that tapered from a radius of 250 to 150 µm. Three gold layers were just diamond turned to wedges to set the tilt of the whole aperture. Three gold layers were profiled on both sides with triangle groove arrays that consist of eight equilateral triangles with the depth of 200 to 15 µm over the 200-mm length, with a tolerance of 2 µm. Custom software programming routines were written using Labview to move the diamond-turning profiler through the required X-Y-Z movements to cut the penumbral and grooved profiles of the pinhole into the varying tilted arrays of features. The software is optimized to push the profile of the whole part into the face while eliminating any unneeded passes that do not cut any material. Each layer was thoroughly inspected on both sides using an optical coordinate measuring machine and white-light interferometer to validate each of the profiles. The pinhole assembly was inspected on a rotary stage so that both ends of the assembly can be inspected and presented in a single point cloud. The process of machining, programming, assembly, and inspection of the neutron imaging pinhole is covered in this paper.