The quenching of o<i>rtho</i> ‐positronium

Hyodo, Toshio; Nakayama, Takashi; Saito, Haruo; Saito, Fuminori; Wada, Ken

doi:10.1002/pssc.200982118

Cited by 20 publications

(9 citation statements)

References 28 publications

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“…Note that MQ is distinct from other quenching mechanisms induced by interactions with external (unpaired) electrons, even though they too involve spin interactions [369]. Annihilation can either occur with an external electron, or the interaction can convert the triplet atom into a singlet state, which then self-annihilates.…”

Section: Stark and Zeeman Effects In N = 2 Psmentioning

confidence: 98%

“…Furthermore, a very broad excitation lineshape was observed, as shown in Figure 17. The underlying cause of this extreme broadening is not yet understood: one possibility is that isolated pores may contain contaminants that are removed from internal voids connected to the vacuum, and which may lead to chemical quenching [369]. The ground state lifetimes in the pores should be close to the vacuum lifetime [248,409], which implies that there is a weaker quenching effect affecting ground state atoms, and a much stronger one affecting excited state atoms.…”

Section: Spectroscopy Of Confined Psmentioning

confidence: 99%

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Experimental progress in positronium laser physics

2018

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Abstract. The field of experimental positronium physics has advanced significantly in the last few decades, with new areas of research driven by the development of techniques for trapping and manipulating positrons using Surko-type buffer gas traps. Large numbers of positrons (typically ≥10 6 ) accumulated in such a device may be ejected all at once, so as to generate an intense pulse. Standard bunching techniques can produce pulses with ns (mm) temporal (spatial) beam profiles. These pulses can be converted into a dilute Ps gas in vacuum with densities on the order of 10 7 cm −3 which can be probed by standard ns pulsed laser systems. This allows for the efficient production of excited Ps states, including long-lived Rydberg states, which in turn facilitates numerous experimental programs, such as precision optical and microwave spectroscopy of Ps, the application of Stark deceleration methods to guide, decelerate and focus Rydberg Ps beams, and studies of the interactions of such beams with other atomic and molecular species. These methods are also applicable to antihydrogen production and spectroscopic studies of energy levels and resonances in positronium ions and molecules. A summary of recent progress in this area will be given, with the objective of providing an overview of the field as it currently exists, and a brief discussion of some future directions.

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Section: Stark and Zeeman Effects In N = 2 Psmentioning

confidence: 98%

Section: Spectroscopy Of Confined Psmentioning

confidence: 99%

Experimental progress in positronium laser physics

2018

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“…15 For spin-conversion process, the o-Ps exchanges one electron ͑which has spin opposite to that of the positron͒ with surrounding paramagnetic mol- ecule, thus the o-Ps is converted to p-Ps and then undergoes self-annihilation by 2␥ emission. In the chemical quenching process, the o-Ps will combine with some molecules and annihilate from this bound state.…”

Section: B Positron Lifetime Measurementsmentioning

confidence: 99%

Spin conversion of positronium inNiO/Al2O3catalysts observed by coincidence Doppler broadening technique

et al. 2010

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High-purity NiO/ Al 2 O 3 catalysts were prepared by mixing NiO and ␥-Al 2 O 3 nanopowders. X-ray diffraction patterns were measured to characterize the grain size and crystalline phase of the nanopowders. Positronannihilation spectroscopy was used to study the microstructure and surface properties of the pores inside the NiO/ Al 2 O 3 catalysts. The positron lifetime spectrum comprises two short and two long lifetime components. The two long lifetimes 3 and 4 correspond to ortho-positronium ͑o-Ps͒ annihilated in microvoids and large pores, respectively. With increasing NiO content in the NiO/ Al 2 O 3 catalysts, both 4 and its intensity I 4 show continuous decrease. Meanwhile, the para-positronium ͑p-Ps͒ intensity, obtained from coincidence Doppler broadening spectra, increases gradually with NiO content. The different variation in o-Ps and p-Ps intensity suggests the ortho-para conversion of positronium in NiO/ Al 2 O 3 catalysts. X-ray photoelectron spectroscopy shows that Ni mainly exists in the form of NiO. The electron-spin-resonance measurements reveal that the ortho-para conversion of Ps is induced by the unpaired electrons of the paramagnetic centers of NiO.

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“…Ortho-positronium (o-Ps) pick-off annihilations can occur when long-lived o-Ps encounters another surface and results when the positron within an o-Ps atom annihilates with an electron of the opposite spin through a variety of processes [1]. In the present apparatus [2], it is possible for a positron incident on a sample to induce secondary electron emission through impact ionization.…”

Section: Introductionmentioning

confidence: 99%

Estimation of Ortho-Positronium Pick-Off Contributions to the Coincident Measurement of the Energy Spectra of Positron-Induced Electrons and Annihilation Gamma Quanta

et al. 2020

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We present preliminary results that were collected using a new positron beam system at the University of Texas at Arlington. The beam allows for the coincident measurement of the energy of positron annihilation gamma photon and time-coincident positron-induced electrons. This system enables the parallel collection of a 2dimensional array of coincident pairs of gamma and electron energies over the full energy range of relevance. Here, we present gamma spectra constructed from the correlation of secondary electrons with the delayed annihilation of positronium, and the observation of pick-off annihilations that results from this analysis. These measurements will play an important role in determining the contributions due to pick-off annihilations to the Doppler-broadened gamma spectra from the internal or external exposed surfaces of materials. Subtracting the background properly is crucial for the measurement of the Doppler broadened spectrum of annihilation gamma photons originating from the annihilation of positrons with electrons of specific electronic core levels.

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The quenching of ortho ‐positronium

Cited by 20 publications

References 28 publications

Experimental progress in positronium laser physics

Experimental progress in positronium laser physics

Spin conversion of positronium inNiO/Al2O3catalysts observed by coincidence Doppler broadening technique

Estimation of Ortho-Positronium Pick-Off Contributions to the Coincident Measurement of the Energy Spectra of Positron-Induced Electrons and Annihilation Gamma Quanta

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