Giant resonances in lead-208 measured by electron scattering with coincident neutrons
Bolme, Gerald Owen
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https://hdl.handle.net/2142/25348
Description
Title
Giant resonances in lead-208 measured by electron scattering with coincident neutrons
Author(s)
Bolme, Gerald Owen
Issue Date
1983
Doctoral Committee Chair(s)
Koester, L.J.
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
giant resonances
lead-208
inelastic electron scattering
coincident neutrons
effective momentum transfers
Language
en
Abstract
The inelastic electron scattering cross sections were measured in the excitation region from 9.0 MeV to 16.0 MeV of 208pb by detection of scattered electrons in coincidence with decay neutrons. The effective momentum transfers of 0.35, 0.41, and 0.47 rm-1 were achieved by detecting the scattered electrons at an angle of 600 relative to the beam axis for incident beam energies of 57.0 MeV, 67.6 MeV, . and
80.35 MeV respectively from the University of Illinois MUSL-2 accelerator. The decay neutrons were detected by two organic liquid scintillator detectors placed antiparallel and perpendicular to the momentum transfer axis at a distance of one meter. The gamma ray background in the neutron detectors was reduced to a very low level through both analog and digital pulse shape discrimination techniques.
The measured cross sections were separated into their E1 and combined E2 + EO components through a multipole decomposition based on the momentum transfer dependence. The combined E2 + EO reduced transition probabilities indicate the presence of two broad resonance peaks on top of a flat distribution spanning the entire excitation
region. The two peaks centered approximately at 10.6 MeV and 14.1 Mev have been assigned the multipolarities of E2 and EO respectively based on hadron scattering.
The excitation region was divided into two segments below and above
12.5 MeV, and the multipolarity of each segment was assigned according to the enclosed peak. The measured strength in the region from 9.0 MeV to 12.5 MeV exhausts (107~32)% of an isoscalar E2 energy weighted sum rule, and the measured strength in the region from 12.5 MeV to 16.0 MeV exhausts (94~28)% of an isoscalar EO energy weighted sum rule.
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