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1

Discrete and Continuous Analysis of Positron Lifetime Spectra: a Comparison

100%

Consolati G., Quasso F.

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vol. 95

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issue 4

505-508

EN

Positron lifetime spectra in poly[1-(trimethylsilyl)]propine membranes were collected at different temperatures and various number of accumulated counts, in order to compare the results from analyses obtained by different decay models: discrete (that is, purely exponential) or continuous (with at least one distribution of lifetimes). Analysis into four discrete components is inadequate, unless a low number of counts (1 to 2 millions) is accumulated. Conversely, deconvolutions which allow the ortho-positronium lifetime to be distributed give satisfactory fits, even at the highest statistics (60 millions). An equivalent good fit in terms of χ^{2} test is obtained with a five discrete components analysis, from which it is possible to extract information on the first moments (centroid and standard deviation) of ortho -positronium lifetime distribution.

2

Quasi-Positronium in Polyethylene Terephthalate - Temperature and Magnetic Quenching Effects

100%

Consolati G., Quasso F.

Acta Physica Polonica A

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1993

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vol. 83

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issue 3

273-276

EN

The features of the positron-electron bound system (quasi-positronium, qPs) in the semicrystalline polymer polyethylene terephthalate (mylar) are obtained while studying the dependence of the ortho-qPs lifetime on temperature in the range of 25-105°C, in the presence as well as in the absence of magnetic fields. In particular, the "anomalous" effect, previously discovered by Bisi et al. at room temperature, is maintained at higher temperature.

3

Outdoor Ageing of an Ethylene-Propylene Copolymer: A Positron Annihilation Study

81%

Consolati G., Quasso F., Gallo R., Severini F.

Acta Physica Polonica A

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2005

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vol. 107

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issue 5

805-810

EN

An investigation on the environmental degradation of an ethylene-propylene copolymer was carried out through positron annihilation lifetime spectroscopy, density and differential scanning calorimetry measurements. Polymer sheets were exposed to sunlight up to 11000 hours. Density and melting enthalpy increase with ageing, while ortho-positronium intensity decreases; ortho-positronium lifetime does not show significant variations up to 4400 hours. At higher exposures it starts to decrease. Outdoor ageing produces an increased crystallinity of the copolymer; also a degradation occurs with formation of carbonyl groups. The corresponding Ps inhibition is the main reason for the decrease in ortho-positronium intensity, the other one being the reduced amount of the amorphous phase available. The lifetime decrease observed at the highest exposures can be interpreted in terms of a shrinking of the nanoholes trapping positronium.

4

Numerical Solution of a Two-Particle Model of Positronium Confined in Small Cavities

81%

Tanzi Marlotti G., Castelli F., Consolati G.

Acta Physica Polonica A

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2017

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vol. 132

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issue 5

1575-1578

EN

The positronium atom (Ps) is widely used as a probe to characterize nanoporous and mesoporous materials. Existing theoretical models for describing Ps annihilation rates by pick-off processes generally treat Ps as a point particle confined in a potential well. Hence these models do not justify any change in the internal structure of Ps, which is experimentally accessible by means of the contact density parameter. Recently we formulated a two-particle model in which only the electron is confined in the cavity, while the positron is moving freely and feels the medium via a positive work function. We present here a numerical treatment of the problem of calculating contact densities and pick-off annihilation rates, by using a variational method. Results are in agreement with experimental data for a large class of materials, and suggest a way to connect these data with pore sizes and positron work functions.

5

Water Sorption and Dessiccation in a Portland Cement Paste: Positron Annihilation Results

81%

Consolati G., Dotelli G., Quasso F.

Acta Physica Polonica A

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2001

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vol. 99

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issue 3-4

345-349

EN

Positron annihilation experiments were carried out on a Portland cement paste one year aged, which was subjected to cycles of dessiccation and subsequent water resaturation, in order to study possible changes of the porosity. Analysis of the annihilation time spectra suggests that drying and rewetting treatments do not induce irreversible modifications in the configuration of the finest gel pores.

6

Production of Cold Positronium Atoms

61%

Brusa R., Mariazzi S., Consolati G., Dupasquier A., Quasso F., Giammarchi M.

Acta Physica Polonica A

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2008

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vol. 113

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issue 5

1301-1306

EN

Positronium will play a primary role in the next generation of antimatter experiments through the following antihydrogen production reaction: p̅ + Ps* → p̅e⁺ + 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.

7

Positronium for Antihydrogen Production in the AEGIS Experiment

23%

Consolati G., Aghion S., Amsler C., Bonomi G., Brusa R., Caccia M., Caravita R., Castelli F., Cerchiari G., Comparat D., Demetrio A., Di Noto L., Doser M., Evans C., Fanì M., Ferragut R., Fesel J., Fontana A., Gerber S., Giammarchi M., Gligorova A., Guatieri F., Haider S., Hinterberger A., Holmestad H., Kellerbauer A., Khalidova O., Krasnicky D., Lagomarsino V., Lansonneur P., Lebrun P., Malbrunot C., Mariazzi S., Marton J., Matveev V., Mazzotta Z., Müller S., Nebbia G., Nedelec P., Oberthaler M., Pacifico N., Pagano D., Penasa L., Petracek V., Prelz F., Prevedelli M., Ravelli L., Rienaecker B., Robert J., Røhne O., Rotondi A., Sandaker H., Santoro R., Smestad L., Sorrentino F., Testera G., Tietje I., Widmann E., Yzombard P., Zimmer C., Zmeskal J., Zurlo N.

Acta Physica Polonica A

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2017

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vol. 132

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issue 5

1443-1449

EN

The primary goal of the Antihydrogen Experiment: Gravity, Interferometry, Spectroscopy (AEGIS) collaboration is to measure for the first time precisely the gravitational acceleration of antihydrogen, H̅, a fundamental issue of contemporary physics, using a beam of antiatoms. Indeed, although indirect arguments have been raised against a different acceleration of antimatter with respect to matter, nevertheless some attempts to formulate quantum theories of gravity, or to unify gravity with the other forces, consider the possibility of a non-identical gravitational interaction between matter and antimatter. We plan to generate H̅ through a charge-exchange reaction between excited Ps and antiprotons coming from the Antiproton Decelerator facility at CERN. It offers the advantage to produce sufficiently cold antihydrogen to make feasible a measurement of gravitational acceleration with reasonable uncertainty (of the order of a few percent). Since the cross-section of the above reaction increases with n⁴, n being the principal quantum number of Ps, it is essential to generate Ps in a highly excited (Rydberg) state. This will occur by means of two laser excitations of Ps emitted from a nanoporous silica target: a first UV laser (at 205 nm) will bring Ps from the ground to the n=3 state; a second laser pulse (tunable in the range 1650-1700 nm) will further excite Ps to the Rydberg state.

Refine search results

Discrete and Continuous Analysis of Positron Lifetime Spectra: a Comparison

Quasi-Positronium in Polyethylene Terephthalate - Temperature and Magnetic Quenching Effects

Outdoor Ageing of an Ethylene-Propylene Copolymer: A Positron Annihilation Study

Numerical Solution of a Two-Particle Model of Positronium Confined in Small Cavities

Water Sorption and Dessiccation in a Portland Cement Paste: Positron Annihilation Results

Production of Cold Positronium Atoms

Positronium for Antihydrogen Production in the AEGIS Experiment