Coincident neutron/proton pairs from 6̳Li photodisintegration with 40-100 MeV photons
Ritchie, Buddy Boyce
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https://hdl.handle.net/2142/18914
Description
Title
Coincident neutron/proton pairs from 6̳Li photodisintegration with 40-100 MeV photons
Author(s)
Ritchie, Buddy Boyce
Issue Date
1991
Doctoral Committee Chair(s)
Brussel, M.K.
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
coincident neutron proton pairs
lithium
photodisintegration
Language
en
Abstract
"Bremsstrahlung photons with endpoint energies from 55 to 100 MeV were used
to photodisintegrate 6Li nuclei, and emitted neutron/proton pairs were observed in
coincidence. Measurement of the energies and angles of the emitted pair allowed
reconstruction of the photon energy, as well as the recoil angle and energy of the
residual 4He nucleus. Cross sections for the 6Li(l,np) reaction were computed by
normalizing the data to measured yields and published cross sections for the 2H( 1 ,np)
reaction.
The 6Li target was in the form of solid metal foil. Protons were detected with
a ~E-E scintillator telescope, and their energy measured by the amount of energy
deposited in the ""E"" element (a Nal crystal). The neutron detector was a large
solid angle array of long plastic scintillator elements. Neutron trajectories were
resolved within the coverage of the array through a combination of detector element
identity and the difference in arrival times of scintillation photons at either end of
that element. Neutron energy was determined by measuring the time of flight of the
neutron over a distance of ~4 m.
Cross sections were measured with the proton detector fixed at 81 o (in the laboratory
frame) for neutron angles of 50-120°. In addition, measurements were made
with detectors at equal angles of 71-101 o on opposite sides of the photon beam.
The singly differential cross section ( da / dO.P) at f)P = 81° was calculated by integrating
over the neutron angle; its ratio to the deuterium cross section varied from
0.26±0.03 at 45 MeV to 0.55±0.12 at 95 MeV. Cross sections were also evaluated
in terms of the recoil momentum of the residual 4He nucleus, which should reflect
the combined momentum of the neutron-proton pair prior to the photoabsorption.
The distribution of recoil momentum transverse to the photon beam had a central
peak of width 96.8±3.5 MeV /c (FWHM); this is consistent with a harmonic oscillator
2s wave function description of the pair-41-Ie relative motion with width parameter
qo = 91.5 ± 3.3 MeV jc."
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