Quenching of positronium by surface paramagnetic centers in ultraviolet- and positron-irradiated fine oxide grains

Saito, Haruo; Hyodo, Toshio

doi:10.1103/physrevb.60.11070

Cited by 40 publications

(37 citation statements)

References 39 publications

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“…These centers can inhibit Ps formation [700] or can convert triplets to singlets via spin exchange [701], and are therefore not compatible with Ps BEC experiments. Moreover, there are many types of paramagnetic center, and often they become more stable at lower temperatures [131,702,703], and thus could present a particularly serious problem for experiments that require cryogenic Ps.…”

Section: Bose-einstein Condensationmentioning

confidence: 99%

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: Bose-einstein Condensationmentioning

confidence: 99%

Experimental progress in positronium laser physics

2018

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“…Since Ps emission times can be comparable to the lifetime in the pores, which may be 10's of ns or more [30], Ps produced by this method may not be optimal for some experiments (for example, excitation with laser pulses that are much shorter than the Ps emission time). Moreover, such materials can be highly susceptible to laser damage even at room temperature [31]; this situation is likely to be worse at lower temperatures [32], and may even lead to significant damage being created by the incident positron beam if it is intense enough [33].…”

Section: Introductionmentioning

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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“…A similar lifetime shortening in alumina powders due to irradiation was reported in [12] and it was ascribed to quenching of surface-bound o-Ps by irradiation-created interstitial atoms migrating to the surface. Similar effects were interpreted as a consequence of reaction with paramagnetic centers on the surfaces in SiO 2 [13] and in fine oxide grains [14]. Our samples are rich in internal grain surfaces and they contain elements (Al, Si, O) suitable for these effects.…”

Section: Resultsmentioning

confidence: 84%

Positron and Positronium Trapping in Heat Treated Zeolites (Ceramics), the Effect of Swift Heavy Ion Irradiation

et al. 2008

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A systematic study of zeolite precursor gels, zeolites, and products of their recrystallization to ceramics was carried out in presence of various alkali ions. The investigation of radiation damage induced by high-energy ion beam irradiation with swift heavy ions (Bi ions at 670 MeV energy with 4×10 12 ion/cm 2 fluence) was also included. The shortening of lifetimes found after irradiation in ceramics might probably be ascribed to interactions of o-Ps with free radicals and other quenching agents created through the ion irradiation. These lifetime-shortening interactions probably partly hide the o-Ps trapping in free volume sites.

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Quenching of positronium by surface paramagnetic centers in ultraviolet- and positron-irradiated fine oxide grains

Cited by 40 publications

References 39 publications

Experimental progress in positronium laser physics

Experimental progress in positronium laser physics

Positronium formation via excitonlike states on Si and Ge surfaces

Positron and Positronium Trapping in Heat Treated Zeolites (Ceramics), the Effect of Swift Heavy Ion Irradiation

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