Degree Type

Dissertation

Date of Award

1990

Degree Name

Doctor of Philosophy

Department

Nuclear Engineering

First Advisor

Monroe Wechsler

Abstract

Characterization of the radiation environment at the Los Alamos Spallation Radiation Effects Facility (LASREF) has been completed. Monte Carlo neutronics calculations, foil activation experiments, and radiation damage calculations were performed to determine the neutron and proton flux and energy spectrum at the LASREF;Thirteen foil activation experiments using high-purity iron, scandium, copper, nickel, vanadium, titanium, aluminum and cobalt foils were irradiated in a "rabbit" dosimetry insert to measure the neutron and proton flux and energy spectrum in neutron irradiation ports outside the IP targets and the beam stop and one proton irradiation port. Cobalt, scandium, and iron foils wrapped with gadolinium were irradiated to measure the epithermal neutron flux. The average proton flux in the proton irradiation port was 4.8 x 10[superscript]13 protons (p)/cm[superscript]2-s-mA. The highest neutron flux, 5.5 x 10[superscript]13 n/cm[superscript]2-s-mA, was measured outside the IP targets. The measured flux compared favorably with the flux calculated using the Monte Carlo programs. Irradiation capsules were stacked on top of each other to measure the neutron flux above, on, and below beam centerline. No difference was seen in these positions except for statistical variation. Irradiation capsules were irradiated in tubes in the dosimetry insert located radially from the beamline to determine radial variations in the flux and energy spectrum. The spectral shape did not change but the flux decreased in the first three tubes. An enhancement for neutron energies below 0.1 MeV was seen in tube four. The magnitude of the flux and the spectral shape varied with the IP target loading;The measured neutron spectrum was used to calculate the differential and total displacement and helium production rates in copper at LASREF using SPECTER and VNMTC computer codes. The total displacement production rate for neutrons was 4 x 10[superscript]-8 displacements per atom (dpa/s). Twenty-six percent was produced by neutrons above 20 MeV. The total helium production rate for neutrons was 7 x 10[superscript]-7 atomic parts per million (appm) He/s. Ninety-five percent was produced by spallation neutrons. The rates for the primary proton beam were 6.3 x 10[superscript]-7 dpa/s and 6.6 x 10[superscript]-5 appm He/s. Calculations show a significant contribution from spallation neutrons and an even higher contribution from the primary proton beam.

DOI

https://doi.org/10.31274/rtd-180813-12950

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/

Copyright Owner

Dorothy R. Davidson

Language

en

Proquest ID

AAI9100425

File Format

application/pdf

File Size

172 pages

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