Evidence for pore surface dependent positronium thermalization in mesoporous silica/hybrid silica films

He, Chunqing; Ohdaira, Toshiyuki; Oshima, Nobuyuki; Muramatsu, Makoto; Kinomura, A.; Suzuki, Ryoichi; Oka, Toshitaka; Kobayashi, Yoshinori

doi:10.1103/physrevb.75.195404

Cited by 50 publications

(30 citation statements)

References 20 publications

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“…However, it is true that the cooling rate decreases as cooling proceeds, so that at some point an additional cooling mechanism may be required. This could be laser cooling, or it could be modified collisional cooling, which can be achieved by introducing low mass molecules that increase the energy loss per collision [280]. Other avenues may also be possible: for example, the availability of narrow velocity distributions hinted at by MOF measurements [124] is a promising area for future research, especially considering the huge number of possible MOF materials.…”

Section: Discussionmentioning

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: Discussionmentioning

confidence: 99%

“…This work has also led to the use of thin mesoporous films that can be used as Ps converters [109,110,[246][247][248][279][280][281][282][283][284]. These materials produce Ps in a similar way to the powders discussed previously [35,36].…”

Section: Ps Productionmentioning

confidence: 99%

Experimental progress in positronium laser physics

2018

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“…The lifetime of a fraction of o-Ps is shortened in the nanoporosities by pick-off annihilation, in which the positron of the o-Ps annihilates with an electron of the walls of the pores into 2 c-rays. Porous silica has proved to be a good choice for converting positrons into cold positronium due to the large Ps yield in the bulk and on the porous surface, combined with the relatively efficient cooling of o-Ps by collisions with the walls of the pores [17][18][19].…”

Section: Introductionmentioning

confidence: 99%

Characterization of a transmission positron/positronium converter for antihydrogen production

Aghion

Amsler

Ariga

et al. 2017

Nuclear Instruments and Methods in Physics Research Section B:

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and 10 ns temporal width. The forward emission of implanted positrons and secondary electrons was investigated with a micro-channel plate -phosphor screen assembly, connected either to a CCD camera for imaging of the impinging particles, or to a fast photomultiplier tube to extract information about their time of flight. The maximum Ps formation fraction was estimated to be $10%. At least 10% of the positrons implanted with an energy of 3.3 keV are forward-emitted with a scattering angle smaller than 50°and maximum kinetic energy of 1.2 keV. At least 0.1-0.2 secondary electrons per implanted positron were also found to be forward-emitted with a kinetic energy of a few eV. The possible application of this kind of positron/positronium converter for antihydrogen production is discussed.

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“…Length L and diameter d of the pore (framed as a cylinder) can be correlated to the number k of collisions: a stochastic approximation for the random walk of a Ps colliding against the walls of the pore and diffusing toward the open end supplies the relation L = d √ k. Within the same approximation the travel time t is related to the pore diameter d and to the average Ps speed v: t = kd √ 2/v. Travel time and average Ps speed can be assumed t ≈ τ oPs /10, v = 4 × 10of collisions strongly depends on the effective mass of atoms on pore walls: we can estimate for k a range k = 1 × 10 5 −3 × 10 5 [16]. With the above data we obtain d ≈ 4-12 nm and L ≈ 2−4 µm.…”

Section: Positron To Ps Conversionmentioning

confidence: 71%

Production of Cold Positronium Atoms

et al. 2008

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Positronium will play a primary role in the next generation of antimatter experiments through the following antihydrogen production reaction: p + Ps * →pe + + e − . In order to study antimatter physical properties (CPT (charge, parity, time) invariance and principle of equivalence test) it is necessary to keep this system at the lowest possible (sub-kelvin) temperatures. This requires the generation of a suitable flux of cold Ps atoms in a vacuum, a non-trivial requirement at the light of the present experimental results. In this paper we discuss the state of the actual knowledge on positronium formation and consequent emission from metallic surfaces and insulators and we show the opportunity to use suitable porous materials to cool positronium through collisions with the inner walls of the pores. We get a rough indication on the geometrical parameters of the pore and we propose a simple experiment to obtain the kinetic energy -and therefore the equivalent temperature -of emitted positronium without using a positron beam.

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Evidence for pore surface dependent positronium thermalization in mesoporous silica/hybrid silica films

Cited by 50 publications

References 20 publications

Experimental progress in positronium laser physics

Experimental progress in positronium laser physics

Characterization of a transmission positron/positronium converter for antihydrogen production

Production of Cold Positronium Atoms

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