Criticality experiments with 235 U (metal and hydride) and 239 Pu (metal) were performed during the Manhattan Project. Results from these experiments provided necessary information for the success of the Manhattan Project. These experiments have been previously described in compilations made after the Manhattan Project, 1-3 but those works are either lacking in technical details or are not publicly available. This work aims to provide detailed information while showcasing the enduring impact of these experiments 75 years after they were performed. Furthermore, we use modern computational methods embodied in the MCNP6 code and ENDF data to analyze and interpret these historic measurements. The world's first four criticality accidents are also discussed, as lessons learned from these helped shape the field of criticality experiments.

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Catalog of sensitivity profiles for 1000s of experiments SU-based Analysis USL Upper Subcritical Limit for criticality safety analysis Nuclear Cross-section Covariance Data Sensitivity-Uncertainty Techniques for Nuclear Criticality Safety 9 Sensitivity-Uncertainty Techniques for Nuclear Criticality Safety 38 Flux Spectra for Neutron Slowing Down & Criticality 2 MeV neutrons hydrogen fission neutrons hydrogen fission neutrons water fission neutrons water + B 10 fission neutrons water + U 238 Fuel Pin Unit Cell loglin plots of φ(u) vs u loglog plots of φ(E) vs E 2 MeV neutrons hydrogen fission neutrons hydrogen fission neutrons water fission neutrons water + B 10 fission neutrons water + U 238 Fuel Pin Unit Cell

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Monte Carlo Codes Group (XCP-3), WHISPER module in LANL TeamForge GIT repository (2015) Monte Carlo Codes Group (XCP-3), MCNP6 module in LANL TeamForge GIT repository Monte Carlo Codes Group (XCP-3), "MCNP Process Documents", LANL Teamforge wiki for MCNP

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