Investigation of the photoneutron cross section in 206Pb and 208 Pb from 9 to 16 MeV

The time of flight of photoneutrons from 206Pb and 208Pb was observed at scattering angles of 55 0 90 0 , and 125 o. Photons with energies between 9 and 16 MeV were used to excite the target nuclei. The incident photon beam was provided by the University of Illinois Tagged Photon Facility and had an effective energy resolution of around 400 keY. Neutron energies were determined by time of flight through a 1.5 meter path. The effective energy resolution of the neutrons was between 7.6% at 1 MeV and 12.5% at 5 MeV. Neutron detector efficiency was determined by measuring the photo-disintegration of deuterium. The resulting efficiency was found to be constant across the neutron energy range of interest. The fraction of neutrons with energy insufficient to pass the detector threshold was estimated to be 10.7%. The total cross section (or both 206Pb and 208Pb are well described by Lorentzian curves with widths of 4.12 ± 0.24 MeV for 206Pb and 4.09 ± 0.38 MeV for 208Pb. The peak positions of the curves were determined to be 13.70 ± 0.06 MeV for 206Pb and 13.53 ± 0.05 MeV in 208Pb. No angular asymmetry about 90 in the differential cross sections was detected in either element above 11 MeV. Below 11 MeV the asymmetry varied with energy between alternate positive and negative values for each element. The time-of-flight spectra could be parameterized for low energy neutrons by a statistical decay with a nuclear temperature of O,g MeV. There was an excess of high energy neutrons above this distribution. A more detailed analysis of the spectra using the Hauser-Feshbach formalism suggests that this excess is also from the statistical decay of the nucleus.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Physics

Year dc:date

2011

Author dc:creator

• Morford, Larry Joe

Contributors dc:contributor

• Debevec, Paul T.

• photoneutron
• incident photon beam
• neutron energies

Statement dc:rights

• 1985 Larry Joe Morford

Language dc:language

en

Identifier

862787

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/25281