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The annihilation of positrons in helium Lee, Gregory Frank
Abstract
Lifetime techniques have been used to investigate the annihilation of positrons in helium as a function of electric field and density. Positronium formation has also been examined as a function of electric field. Results obtained for zero electric field yielded a linear dependence of the direct annihilation rate on density of (0.7214 ± .0082)D x 10⁶ sec⁻¹ amagat⁻¹, with no evidence of non-linearity. This corresponds to a Zeff of 3.628 ± .041. Assuming the free ortho-positronium annihilation rate of 7.2 x 10⁶ sec⁻¹ a value of (0.0991 ± .0067) x 10⁶ sec amagat⁻¹ was obtained for the ortho-positronium quenching rate. A dependence of the direct annihilation rate on applied electric field was observed and compared with several current theories describing the positron-helium interaction. The predictions of the theory of Drachman (1968) are shown to be in closest agreement. Measurement of the amount of positronium formed as a function of electric field disagrees with previous results and based on the present work a value for the momentum-transfer cross-section of positrons in helium at 17.7 ev is found to be at least .135π a₀² .
Item Metadata
Title |
The annihilation of positrons in helium
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Creator | |
Publisher |
University of British Columbia
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Date Issued |
1969
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Description |
Lifetime techniques have been used to investigate the annihilation
of positrons in helium as a function of electric field and density.
Positronium formation has also been examined as a function of electric field.
Results obtained for zero electric field yielded a linear dependence
of the direct annihilation rate on density of (0.7214 ± .0082)D x 10⁶
sec⁻¹ amagat⁻¹, with no evidence of non-linearity. This corresponds to
a Zeff of 3.628 ± .041. Assuming the free ortho-positronium annihilation rate of 7.2 x 10⁶ sec⁻¹ a value of (0.0991 ± .0067) x 10⁶ sec amagat⁻¹ was obtained for the ortho-positronium quenching rate.
A dependence of the direct annihilation rate on applied electric
field was observed and compared with several current theories describing the positron-helium interaction. The predictions of the theory of Drachman (1968) are shown to be in closest agreement.
Measurement of the amount of positronium formed as a function of
electric field disagrees with previous results and based on the present
work a value for the momentum-transfer cross-section of positrons in
helium at 17.7 ev is found to be at least .135π a₀² .
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Genre | |
Type | |
Language |
eng
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Date Available |
2011-08-24
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Provider |
Vancouver : University of British Columbia Library
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Rights |
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.
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DOI |
10.14288/1.0103738
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URI | |
Degree | |
Program | |
Affiliation | |
Degree Grantor |
University of British Columbia
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Campus | |
Scholarly Level |
Graduate
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Aggregated Source Repository |
DSpace
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Item Citations and Data
Rights
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.