Multi-photon decay mode spectroscopy of positronium
| dc.contributor.advisor | Leadbeater, Thomas | |
| dc.contributor.advisor | Jones, Pete | |
| dc.contributor.author | Johnson, Storm | |
| dc.date.accessioned | 2022-06-10T10:11:07Z | |
| dc.date.available | 2022-06-10T10:11:07Z | |
| dc.date.issued | 2022 | |
| dc.date.updated | 2022-06-10T10:10:13Z | |
| dc.description.abstract | An approximation for the branching ratio of the four-photon decay of parapositronium (BR4γ) was measured using a multi-gamma-ray spectrometer. For the first time in such measurements, the spectrometer consisted of an array of eight identical LaBr3:Ce scintillator detectors, each of which combines good energy resolutions (5% and 10% at 511 keV for the signals from the eighth dynode and anode of the photomultiplier tube, respectively) with an excellent timing resolution (∼ 300 ps). These energy resolutions were minimised through an optimal selection of the digital signal processing parameter settings. The detectors were situated in a planar geometry, where the source-to-detector distance of the detector system was selected such that the effect of peak pulse pile-up was minimised (to less than 3%), while maximising the full-energy peak detection efficiency at 511 keV (to 3%). For this work, locally-produced 22Na radioactive sources were used as positron emitters, which enabled the formation of positronium and subsequent gamma decays. Energy calibration measurements were performed using a 152Eu source, where the prominent energy peaks of (121.8, 244.7, 344.3, 778.9, 964.1, 1408.0) keV were used for calibration. For the BR4γ measurement, 5×1011 events were accumulated over a measurement period of 60 days, which resulted in low statistical uncertainties for the coincident counting between detector pairs (less than 1%). Through simplifying assumptions that neglected the background corrections and efficiency normalisations for each of the 2γ and 4γ decays, a first order approximation of BR4γ was determined as the ratio between measured 4γ events (N4γ) and measured 2γ events (N2γ), such that BR4γ ∼ N4γ N2γ = 4.8 (19) × 10−7. This measured value of BR4γ differs from previous measurements and accepted literature values by a factor of 3. | |
| dc.identifier.apacitation | Johnson, S. (2022). <i>Multi-photon decay mode spectroscopy of positronium</i>. (). ,Faculty of Science ,Department of Physics. Retrieved from http://hdl.handle.net/11427/36466 | en_ZA |
| dc.identifier.chicagocitation | Johnson, Storm. <i>"Multi-photon decay mode spectroscopy of positronium."</i> ., ,Faculty of Science ,Department of Physics, 2022. http://hdl.handle.net/11427/36466 | en_ZA |
| dc.identifier.citation | Johnson, S. 2022. Multi-photon decay mode spectroscopy of positronium. . ,Faculty of Science ,Department of Physics. http://hdl.handle.net/11427/36466 | en_ZA |
| dc.identifier.ris | TY - Master Thesis AU - Johnson, Storm AB - An approximation for the branching ratio of the four-photon decay of parapositronium (BR4γ) was measured using a multi-gamma-ray spectrometer. For the first time in such measurements, the spectrometer consisted of an array of eight identical LaBr3:Ce scintillator detectors, each of which combines good energy resolutions (5% and 10% at 511 keV for the signals from the eighth dynode and anode of the photomultiplier tube, respectively) with an excellent timing resolution (∼ 300 ps). These energy resolutions were minimised through an optimal selection of the digital signal processing parameter settings. The detectors were situated in a planar geometry, where the source-to-detector distance of the detector system was selected such that the effect of peak pulse pile-up was minimised (to less than 3%), while maximising the full-energy peak detection efficiency at 511 keV (to 3%). For this work, locally-produced 22Na radioactive sources were used as positron emitters, which enabled the formation of positronium and subsequent gamma decays. Energy calibration measurements were performed using a 152Eu source, where the prominent energy peaks of (121.8, 244.7, 344.3, 778.9, 964.1, 1408.0) keV were used for calibration. For the BR4γ measurement, 5×1011 events were accumulated over a measurement period of 60 days, which resulted in low statistical uncertainties for the coincident counting between detector pairs (less than 1%). Through simplifying assumptions that neglected the background corrections and efficiency normalisations for each of the 2γ and 4γ decays, a first order approximation of BR4γ was determined as the ratio between measured 4γ events (N4γ) and measured 2γ events (N2γ), such that BR4γ ∼ N4γ N2γ = 4.8 (19) × 10−7. This measured value of BR4γ differs from previous measurements and accepted literature values by a factor of 3. DA - 2022 DB - OpenUCT DP - University of Cape Town KW - Physics LK - https://open.uct.ac.za PY - 2022 T1 - Multi-photon decay mode spectroscopy of positronium TI - Multi-photon decay mode spectroscopy of positronium UR - http://hdl.handle.net/11427/36466 ER - | en_ZA |
| dc.identifier.uri | http://hdl.handle.net/11427/36466 | |
| dc.identifier.vancouvercitation | Johnson S. Multi-photon decay mode spectroscopy of positronium. []. ,Faculty of Science ,Department of Physics, 2022 [cited yyyy month dd]. Available from: http://hdl.handle.net/11427/36466 | en_ZA |
| dc.language.rfc3066 | eng | |
| dc.publisher.department | Department of Physics | |
| dc.publisher.faculty | Faculty of Science | |
| dc.subject | Physics | |
| dc.title | Multi-photon decay mode spectroscopy of positronium | |
| dc.type | Master Thesis | |
| dc.type.qualificationlevel | Masters | |
| dc.type.qualificationlevel | MSc |