Positronium Decay in Molecular Substances

Brandt, Werner; Berko, S.; Walker, William W.

doi:10.1103/physrev.120.1289

Cited by 309 publications

(148 citation statements)

References 20 publications

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“…for T g < T < 5 0 0 K (1) and in the glassy state by ( 2 ) with the temperature T i n K. Maximum deviations from the exact solution never exceed 0.0003 within the given validity ranges of eqs.…”

Section: Free Volume Calculationsmentioning

confidence: 97%

See 1 more Smart Citation

Monte Carlo calculations of hole size distributions: Simulation of positron annihilation spectroscopy

Vleeshouwers

Kluin

McGervey

et al. 1992

J Polym Sci B Polym Phys

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SYNOPSISConsequences are explored of a hole size distribution in an amorphous polymer for the ortho-positronium (0-Ps) lifetime ( T~) and intensity ( Z3), determined by positron annihilation lifetime spectroscopy. The disordered lattice model, with a vacancy fraction h as a central quantity, is used to represent the equation-of-state behavior of the polymer. By means of Monte Carlo simulations, we obtain the cluster size distribution as a function of h and hence temperature. The predicted average cluster size and the cluster concentration are compared to T~ and I3 data, respectively, for bisphenol-a polycarbonate. Furthermore, the influence of an 0-Ps lifetime distribution on the experimental mean 7 3 is investigated. By mimicking the computational methods used in experimental analysis, agreement between experiment and theory in respect to 73 and to Z3 in the melt ensues. In the glass, however, the experimental Z, becomes increasingly smaller with decreasing temperature than is computed. These deviations may result from a distortion of the equilibrium free volume. 0 1992

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Section: Free Volume Calculationsmentioning

confidence: 97%

“…(1) or eq. (2). The number-averaged cluster size ( n ) can be calculated by and the total cluster concentration N,, by…”

Section: C Calculationsmentioning

confidence: 99%

Monte Carlo calculations of hole size distributions: Simulation of positron annihilation spectroscopy

Vleeshouwers

Kluin

McGervey

et al. 1992

J Polym Sci B Polym Phys

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show abstract

“…However, by definition, this assumption gives no information about contact densities. Another family of models consider both Ps constituent particles as independent but confined into the cavity [5,6], or interacting with the material through effective potentials [7], or finally forming a bubble-like state in a dielectric medium with special assumption about work functions [8]. Only the last model can describe the wellknown observation that the contact density is usually found to be well below the vacuum value, while all other models predict an increase.…”

Section: Introductionmentioning

confidence: 99%

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

2017

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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 twoparticle 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.

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“…The work of Deutsch and colleagues did not immediately provoke widespread experimental Ps research, although in the following decades some measurements were conducted, including studies of magnetic quenching [29][30][31] and electric field effects on Ps in gases [32], (unsuccessful) searches for Ps Lyman alpha lines [33], measurements of Ps formation [34] and diffusion [35] in solid materials, powders [36], and liquids [37], positron polarization measurements [38], symmetry tests [39] and more refined hyperfine interval measurements [40], as well as Ps decay rate measurements [41]. All of this work utilized positrons emitted from radioactive sources and captured in the material in which Ps formation occurred.…”

Section: Introductionmentioning

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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Positronium Decay in Molecular Substances

Cited by 309 publications

References 20 publications

Monte Carlo calculations of hole size distributions: Simulation of positron annihilation spectroscopy

Monte Carlo calculations of hole size distributions: Simulation of positron annihilation spectroscopy

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

Experimental progress in positronium laser physics

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