Positronium Cooling and Emission in Vacuum from Nanochannels at Cryogenic Temperature

Mariazzi, S.; Bettotti, Paolo; Brusa, R. S.

doi:10.1103/physrevlett.104.243401

Cited by 107 publications

(104 citation statements)

References 31 publications

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“…Other elemental and compound semiconductors that have dangling bond states should produce Ps via the same basic mechanism, and by varying their properties it may be possible to adjust the Ps energy. An efficient source of cold Ps that may be used in a low temperature environment, and that allows for the production of short-time bursts of positronium atoms [77] could have numerous experimental applications, including direct Ps gravity measurements [78], the formation of antihydrogen atoms via Ps-antiproton interactions [79], Psatom scattering [7], loading a stellerator to study electronpositron plasmas [80], the production of positron-atom bound states [81] and precision laser spectroscopy [4,82]. Any type of experiment involving Ps-laser interactions would benefit from an efficient source of monoenergetic Ps, since the Doppler spread of these light atoms (~ 500 GHz for thermal Ps) is in general much larger than typical laser bandwidths and is the limiting factor in the excitation efficiency.…”

Section: Discussionmentioning

confidence: 99%

Positronium formation via excitonlike states on Si and Ge surfaces

et al. 2011

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Recent experiments combining lifetime and laser spectroscopy of positronium (Ps) show that these atoms are emitted from p-Si(100) at a rate that depends on the sample temperature, suggesting a thermal activation process, but with an energy that does not, precluding direct thermal activation as the emission mechanism. Moreover, the amount of Ps emitted is substantially increased if the target is irradiated with 532 nm laser light just prior to the implantation of the positrons. Our interpretation of these data was that the Ps was emitted via an exciton-like positron-electron surface state, not dissimilar to an electronic surface exciton observed on Si in two-photon photoemission measurements. The hypothesis that this state may be populated by electrons from one of the occupied electronic surface states, either thermally or by laser excitation, is consistent with our observations and suggests that one should expect a high Ps yield at room temperature from an n-doped Si(100) sample, since in this case the same surface states will already be occupied. Here we present data obtained with an n-Si(100) target that supports our model, and also reveals the unexpected result that the kinetic energy of Ps emitted from this material actually decreases when it is heated, an effect we attribute to shifts in the surface energy levels due to the presence of a high density of thermally generated electrons. We show data obtained with a Ge(100) sample that corroborate the idea that the effects we observe are related to surface electron states, and hence should occur for any indirect band gap semiconductor with dangling bond states. Our model is further confirmed by the observation that the Ps yield from p-Si depends linearly on the surface density of the implanted positrons due to the effects of electron-hole pairs created as the positrons slow down.

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Section: Discussionmentioning

confidence: 99%

Positronium formation via excitonlike states on Si and Ge surfaces

et al. 2011

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“…In the target, e + were efficiently converted into o-Ps and emitted into vacuum [35,36]. A calibrated CsI detector and a microchannel plate (MCP) with a phosphor screen, set in place of the target, were used to characterize the number and the spot dimension of positrons impinging on the target.…”

Section: Experimental Methodsmentioning

confidence: 99%

Producing long-lived 23S positronium via 33P laser excitation in magnetic and electri

Aghion¹,

Amsler²,

Antonello³

et al. 2018

Phys. Rev. A

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Producing positronium (Ps) in the metastable 2 3 S state is of interest for various applications in fundamental physics. We report here on an experiment in which Ps atoms are produced in this long-lived state by spontaneous radiative decay of Ps excited to the 3 3 P level manifold. The Ps cloud excitation is obtained with a UV laser pulse in an experimental vacuum chamber in presence of guiding magnetic field of 25 mT and an average electric field of 300 V cm −1 . The evidence of the 2 3 S state production is obtained to the 3.6σ level of statistical significance using a novel analysis technique of the single-shot positronium annihilation lifetime spectra. The dynamic of the Ps population on the involved levels has been studied with a rate equation model.

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“…1. A bunch of positrons impinging on a Si target with oriented oxidized nanochannels [22,23] produced copious Ps emission in vacuum. Ps excitation was measured by means of the single shot positron annihilation lifetime spectroscopy (SSPALS) technique [24].…”

Section: Positron Confinement Ps Formation and Excitationmentioning

confidence: 99%