Identification of ortho-positronium annihilation sites in Y zeolites by positron lifetime measurements in different environments

Chiari, Luca; Noguchi, Haruka; Michishio, Koji

doi:10.1016/j.radphyschem.2023.111470

Radiation Physics and Chemistry

2024

DOI: 10.1016/j.radphyschem.2023.111470

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Identification of ortho-positronium annihilation sites in Y zeolites by positron lifetime measurements in different environments

Luca Chiari,

Haruka Noguchi,

Koji Michishio

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2024

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Ortho-positronium annihilation processes in Y zeolites under different environments by measurements of the energy spectra of the positron annihilation radiation

Noguchi,

Chiari

2024

Eur. Phys. J. D

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Measurements of the energy distribution of the positron annihilation radiation in Y zeolites are carried out to elucidate the various ortho-positronium annihilation processes that take place in these microporous materials and relate them to the ortho-positronium lifetime components observed by positron annihilation lifetime spectroscopy in earlier studies. Y zeolites with various Si/Al ratios in the range from 2.6 to 40 are investigated under a controlled atmosphere of N2 gas and after exposure to the atmosphere. The ortho-positronium annihilation modes are characterized by analyzing the γ-ray spectra through the use of the f3γ index, which represents the fraction of 3γ-annihilation, and the S parameter. The proportion of ortho-positronium self-annihilation is found to be no less than 15% in N2 gas, but drastically decreases by the physisorption of water molecules and possibly positronium spin exchange interaction with oxygen in the atmosphere. The presence of water molecules suppresses ortho-positronium intrinsic annihilation and, at the same time, promotes ortho-positronium pick-off annihilation in the pores. Similarly, the S parameter rises due to an increased contribution from para-positronium annihilation and ortho-positronium pick-off annihilation, which is also consistent with the physisorption of water and positronium spin exchange. In conjunction with the previously measured ortho-positronium lifetime components, the specific ortho-positronium annihilation sites and processes in these porous materials under different environments are determined and a complete picture of the ortho-positronium behavior in Y zeolites is obtained. Graphical abstract

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Ortho-positronium annihilation processes in Y zeolites under different environments by measurements of the energy spectra of the positron annihilation radiation

Noguchi,

Chiari

2024

Eur. Phys. J. D

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Identification of ortho-positronium annihilation sites in Y zeolites by positron lifetime measurements in different environments

Cited by 1 publication

References 42 publications

Ortho-positronium annihilation processes in Y zeolites under different environments by measurements of the energy spectra of the positron annihilation radiation

Ortho-positronium annihilation processes in Y zeolites under different environments by measurements of the energy spectra of the positron annihilation radiation

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