Differential cross sections for the reaction He[superscript 3] ([gamma],[rho]) H[superscript 2] from 45 to 150 MeV
O'Fallon, Nancy Marie McCumber
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https://hdl.handle.net/2142/25064
Description
Title
Differential cross sections for the reaction He[superscript 3] ([gamma],[rho]) H[superscript 2] from 45 to 150 MeV
Author(s)
O'Fallon, Nancy Marie McCumber
Issue Date
1966
Doctoral Committee Chair(s)
Koester, L.J.
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
differential cross sections
deuteron telescope
proton telescope
particle identification
Language
en
Abstract
Differential cross sections for the reaction He 3 (y,p)H2
were measured for photons of 45 to 150 MeV at five angular
settings: (theta p , theta d) = (30°, 142°) I (60°, 106°), (90° I 75°),
(120°, 47.5°), and (135°, 34.5°) in the laboratory. At ep
of 60° and 90°, [equation] was obtained for photon energies down to
40 MeV. A gaseous He3 target at about 4°K and slightly less
than one atmosphere pressure was bombarded with 250 MeV
bremsstrahlung. The deuteron detection system, which was a
telescope of three semiconductor detectors followed by a
plastic scintillator, actually defined the solid angle. The
proton telescope of four plastic scintillators was large enough
to intercept all protons correlated with deuterons in the
deuteron telescope. Photographs were made of the pulses from
the detectors as displayed on an oscilloscope whenever there
was a coincidence between a proton in the. proton telescope
and a deuteron in the deuteron telescope. Pulse heights were
used for particle identification and energy assignment.. The
theta p = 90° cross sections ranged from 12.68 Z 0.45ub/sr to
1.07 ± 0.14ub/sr as photon energy increased. These 90° cross
sections join quite smoothly with results of previous experiments.
The total cross section as a function of photon energy,
obtained by integrating the differential cross sections, decreased
from 146 Z 5~b to 14 ~ 2~b as photon energy increased
from 45 to 150 MeV. Integrated and bremsstrahlung-weighted
cross sections obtained from the data of this experiment
combined with data of lower energy experiments and of threebody
photodisintegration experiments are 58.9 ~ 4.0 MeV rnb and
2.46 plus/minus .14 mb, respectively. Both values are in reasonable
agreement with sum rule calculations, and the integrated cross
section is in excellent agreement with a model-independent
dispersion theoretic calculation which includes effects of
all multipoles of electric interaction. It was not possible
to fit the total cross section with the expression derived
for electric dipole transitions with the Gunn and Irving wave
function for the ground state of He3 for any reasonable value
of the size parameter. With the size parameter that fits the
low energy data, the calculated high energy cross sections
are roughly a factor of two down from the measured cross
sections.
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