Graduate Thesis Or Dissertation
 

Verifying safe use of a thinner aluminum scattering chamber for fission physics

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/4f16cb882

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  • This thesis describes calculations done to determine the radiation hazard of the current Prompt Gamma Neutron Activation Analysis (PGNAA) scattering chamber at the Oregon State TRIGA Reactor (OSTR) and compare it to the amount that would be given off by a new thin-walled chamber design. These calculations were completed with the Monte Carlo N-Particle Transport Code (MCNP) and is composed of two main sets of calculations. The first calculations use a given model of the scattering chamber, with a sample of 235U subjected to a neutron flux at three different energies, – 5 eV, 150 keV, and 2 MeV. These represent a wide range of neutron energies that are available from the reactor. Neutrons scatter from the ~ 1 cm focus, then, through collisions, its surrounding area, posing a potential radiation hazard to operators. The second analysis looks at the inverse challenge, as future fission physics studies will need the maximum transmission of gamma rays and X-rays. In these calculations, the target is assumed to have been hit by neutrons from the beamline, and work tracks the potential gammas that would be coming off at a wide range of energies. Both the current scattering chamber design and the new thin-walled design were modeled in order to simulate these constraints, minimizing the attenuation of gammas, while examining the influence on neutron dose. The hypothesis of this experiment was that, while the thin-walled scattering chamber design should see less attenuation of both neutrons and gammas than the current design, the differences should be small enough to where the current design can be replaced without undue hazard. The results showed that not only was this hypothesis correct, but that the difference was far smaller than what was originally considered at risk. Multiple analyses confirm this, and they are outlined in the thesis below. Due to the much greater transmission of low-energy photons, a scattering chamber using the much thinner wall will enable much more sensitive detection of X-rays than the current design.
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