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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.”
Antoaneta Roca, Yuan-Hao Liu, Ray Moss, Finn Stecher-Rasmussen, Sander Nievaart
Nuclear Technology | Volume 168 | Number 1 | October 2009 | Pages 29-34
Detectors | Special Issue on the 11th International Conference on Radiation Shielding and the 15th Topical Meeting of the Radiation Protection and Shielding Division (Part 1) / Radiation Protection | doi.org/10.13182/NT09-A9096
Articles are hosted by Taylor and Francis Online.
The neutron and gamma dose in boron neutron capture therapy (BNCT) can be determined by using ionization chambers of different materials. However, inexplicable results, such as negative doses, are sometimes obtained. Computer simulations using MCNPX can help one to understand the behavior of ionization chambers. This paper deals with a part of this investigation: the contribution of protons to the total measured charge in a tissue equivalent (TE) ionization chamber that is flushed with methane-based TE gas. The inherent problem is that the Monte Carlo code MCNPX cannot track protons below 1 MeV.A custom-made program, called Proton Produced Ionization Chamber Charge (PPICC), calculates the deposited energy and thus the charge in the TE gas per proton. For this, it uses the stopping powers for protons in TE plastic and gas. MCNPX provides the total number of protons produced by all neutron interactions near the gas. To check this new procedure, measurements and simulations have been performed using a validated mixed beam of neutrons and gammas. The neutron fluence consists of 12% fast neutrons and 87% epithermal neutrons. In one setup the chamber is free-in-air (epithermal/fast neutron field) and in the other is in a cubic polymethylmethacrylate phantom at 25 mm depth (thermal/epithermal neutron field).The total charge is the sum of the charges due to electrons, originating from primary and neutron-induced gammas, and protons from 1H(n,n)1H and 14N(n,p)14C reactions. The total measured and calculated charges in the two setups have acceptable uncertainties and are in good agreement. The charge collected in a TE ionization chamber can be simulated in a mixed field of neutrons and gammas. The charge resulting from proton recoil in the gas is unexpectedly large.
