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Scholarly Works (3 results)

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UC Riverside Electronic Theses and Dissertations (2021)

Positronium (Ps) continues to prove itself an ideal candidate for studying various topics in physics, from conducting a precise test of bound-state quantum electrodynamics theory to the creation of the first Ps Bose-Einstein Condensate. Positrons from a sodium-22 radioactive isotope are moderated, trapped, transported, and focused onto a small spot on a suitable target. Mesoporous silica thin film targets yield considerable positronium formation, thereafter magnetic quenching creates majority singlet-state Ps annihilating into two gamma rays with deviations from collinearity resolved to 0.1 mrad with an Angular Correlation of Annihilation Radiation (ACAR) spectrometer. The construction of said spectrometer is detailed, including the characterization of the detectors, power supply, and data collection devices used. The spectrometer will be used for measuring the thermalization rate of positronium as well as material defect studies.

    Cover page: Thermalization Rate of Positronium in Mesoporous Silica Thin Films Studied With Angular Correlation of Annihilation Radiation SpectrometryCreative Commons 'BY-SA' version 4.0 license
    • Article
    • Peer Reviewed
    UC Riverside Previously Published Works (2022)
      Creative Commons 'BY' version 4.0 license
      • Article
      • Peer Reviewed
      UC Riverside Previously Published Works (2022)
      Abstract: The quest for making a triplet positronium (Ps) Bose–Einstein condensate confined in a micron-sized cavity in a material such as porous silica faces at least three interrelated problems: (1) About 107 10 7 spin polarized Ps atoms must be injected into a small cavity within a porous solid material without vaporizing it. (2) It is known that Ps atoms confined in 30–100 nm diameter cavities in porous silica do not remain in the gas phase, but become stuck to the cavity walls at room temperature (Cooper et al., Phys. Rev. B 97:205302, 2018). (3) Cooling a gas of Ps atoms to cryogenic temperatures by energy exchange with the walls would be a very slow process (Saito and Hyodo, in: Surko, Gianturco (eds) New Directions in Antimatter Chemistry and Physics, Springer Dordrecht, Netherlands, 2001) because of the relatively low collision rate with the walls and the large mismatch between the masses of the Ps and the wall atoms. A possible solution of these difficulties is presented, based on cooling the implanted positrons in an isotopically pure diamond single crystal target, subsequent saturating of the wall Ps coverage so that a substantial portion of the Ps will be in the gaseous state, and thermalizing the gas-phase Ps via collisions with the low effective mass wall Ps. A design process for the target material is outlined as well, including preliminary results in porous cavity fabrication using focused ion beam milling. Graphical abstract:
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