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  General Kenneth Nichols and the Manhattan Project
  Nichols
  The Oak Ridger has published the latest in a series of articles about General Kenneth D. Nichols, the Manhattan Project, and the 1954 Atomic Energy Act. The series has been produced by Nichols’ grandniece Barbara Rogers Scollin and Oak Ridge (Tenn.) city historian David Ray Smith. Gen. Nichols (1907–2000) was the district engineer for the Manhattan Engineer District during the Manhattan Project.
  As Smith and Scollin explain, Nichols “had supervision of the research and development connected with, and the design, construction, and operation of, all plants required to produce plutonium-239 and uranium-235, including the construction of the towns of Oak Ridge, Tennessee, and Richland, Washington. The responsibility of his position was massive as he oversaw a workforce of both military and civilian personnel of approximately 125,000; his Oak Ridge office became the center of the wartime atomic energy’s activities.”
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Single- and polycrystalline tungsten samples were implanted with 30 keV³He ions to fluences of 5e16, 4e17 and 5e18 He/cm² at temperatures ranging from ~850 - 1000 °C. After implantation tungsten's retention characteristics were studied using ³He(d,p)⁴He nuclear reaction analysis (NRA) and ³He(n,p)T neutron depth profiling (NDP). Morphological analyses included scanning electron microscopy (SEM), focused ion beam (FIB) milling, and X-ray diffraction on the single crystalline W samples (XRD).

SEM analysis showed that the threshold forsurface pore formation occurs in both single-crystalline tungsten (SCW) and polycrystalline tungsten (PCW) between ~5e16 - 4e17 He⁺/cm². Both surface and sub-surface pore formation is observed to increase with higher implant fluences. Focused ion beam (FIB) milling revealed a sub-surface porous layer in both SCW and PCW, which increased in depth with implanted fluences. NRA measured the retained He fluence in SCW between 1.1e16 - 1.1e17 He/cm² and in PCW between 1.3e17 - 1.5e17 He/cm². NDP analysis measured the retained He fluence in SCW between 2.0e16 - 2.7e17 He/cm² and in PCW between 4.1e16 - 3.2e17 He/cm². Both of these analysis techniques reveal that the retained helium saturates in both single and polycrystalline W at ~4e17 cm^-2. The NDP analysis showed that the peak helium concentration shifted deeper into the specimens as the dose was increased, indicating a decrease in the effective density of the surface layer with an increased dose. Average retained helium concentrations were found to range from 0.7 - 8.6 at% in SCW and from 1.3 - 11.4 at% in PCW.