A MEASUREMENT OF THE PROMPT FISSION NEUTRON ENERGY SPECTRUM FOR ²³⁵U(n,f) AND THE NEUTRON-INDUCED FISSION CROSS SECTION FOR ²³⁸U(n,f)

Author

Zachariah W. Miller, University of KentuckyFollow

Date Available

4-21-2015

Year of Publication

2015

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Arts and Sciences

Department/School/Program

Physics and Astronomy

First Advisor

Dr. Michael A. Kovash

Abstract

Two measurements have been made, addressing gaps in knowledge for ²³⁵U(n,f) and ²³⁸U(n,f). The energy distribution for prompt fission neutrons is not well-understood below 1 MeV in ²³⁵U(n,f). To measure the ²³⁵U(n,f) prompt fission neutron distribution, a pulsed neutron beam at the WNR facility in Los Alamos National Laboratory was directed onto a ²³⁵U target with neutron detectors placed 1 m from the target. These neutron detectors were designed specifically for this experiment and employed a unique geometry of scintillating plastic material that was designed to reject backgrounds. Fission fragments were detected using an avalanche counter. Coincidences between fission fragment production and neutron detector events were analyzed, using a double time-of-flight technique to determine the energy of the prompt fission neutrons. A separate measurement was made, investigating the neutron-induced fission cross section for ²³⁸U(n,f). This measurement also used the pulsed neutron beam at the WNR facility. The neutron flux was normalized to the well-known hydrogen standard and the fission rate was observed for beam neutrons in the energy range of 130-300 MeV. Using an extrapolation technique, the energy dependence of the cross section was determined. These new data filled a sparsely populated energy region that was not well-studied and were measured relative to the hydrogen standard, unlike the majority of available data. These data can be used to constrain the fission cross section, which is considered a nuclear reaction standard.

Recommended Citation

Miller, Zachariah W., "A MEASUREMENT OF THE PROMPT FISSION NEUTRON ENERGY SPECTRUM FOR ²³⁵U(n,f) AND THE NEUTRON-INDUCED FISSION CROSS SECTION FOR ²³⁸U(n,f)" (2015). Theses and Dissertations--Physics and Astronomy. 29.
https://uknowledge.uky.edu/physastron_etds/29