General trends of positronium pick-off annihilation in molecular substances

Dutta, Dhanadeep; Ganguly, Bichitra Nandi; Gangopadhyay, Debarshi; Mukherjee, Tapas; Dutta-Roy, Binayak

doi:10.1088/0953-8984/14/32/313

Cited by 30 publications

(25 citation statements)

References 34 publications

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“…R 1 R qðrÞz eff j WðrÞj 2 r 2 dr in Eq. (1), which physically means the arrangement of electron density surrounding Ps could solely bring about the changes within the annihilation rate constant k, which can also account for the free volume changes as calculated from [21], in Fig. 5, in absence of any chemical changes in the system.…”

Section: Low Temperature Studies With Palsmentioning

confidence: 96%

“…In order to introduce the diffusivity, roughness at the walls of the cavity and the corrections due to the finite size of Ps, a lumped parameter with the dimension of length has been introduced. The model has been described systematically in [21]. The cavity size (R) ( Table 1) calculated using this smooth boundary potential is found to be $3.45…”

Section: Room Temperature Studiesmentioning

confidence: 99%

“…3 r k ep C e ðr; tÞC p ðr; tÞ: The changes of the free volume (V ) with the temperature (T) for the polyamide sample calculated from[21] solely on the basis of Eq. (1), in absence of any chemical interaction.…”

mentioning

confidence: 99%

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Insignia of positronium–molecular interaction in polyamide membrane material

Dutta

Bhattacharyya

Chatterjee

et al. 2003

Chemical Physics Letters

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Section: Low Temperature Studies With Palsmentioning

confidence: 96%

Section: Room Temperature Studiesmentioning

confidence: 99%

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Insignia of positronium–molecular interaction in polyamide membrane material

Dutta

Bhattacharyya

Chatterjee

et al. 2003

Chemical Physics Letters

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“…Another independent measurable quantity is the rate of pickoff annihilation λ PO , well studied by many authors [3,6,8,12,15,21]. The annihilation rate of o-Ps in a small cavity is largely dominated by pickoff and can be expressed as…”

mentioning

confidence: 99%

Positronium Confinement in Small Cavities: A Two-Particle Model for the Lowering of Contact Density

2016

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Positronium (Ps) is widely used as a probe for studying nanometric porosities in condensed matter. Accessible experimental measurements concern annihilation rates by pickoff processes and contact densities (the electron density at the positron position). Existing models for describing Ps properties in small cavities do not justify the lowering of the contact density with respect to that of Ps in vacuum, as found in most materials. We formulate 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. Our calculation fully explains experimental data for a large class of materials and suggests a way to gain information on pore sizes and positron work functions. DOI: 10.1103/PhysRevLett.116.033401 Positronium (Ps) is a hydrogenlike bound state of an electron and its antiparticle, the positron. Ps can exist in two different states: the singlet state p-Ps, rapidly decaying into 2γ rays with a lifetime of 0.125 ns, and the triplet state o-Ps annihilating in 3γ rays with a lifetime of 142 ns in vacuum [1]. Ps is usually formed by implanting positrons in condensed matter. Many insulators and molecular solids allow Ps formation, sometimes with high efficiency; when generated near the surface (e.g., by using a slow positron beam) Ps can rapidly spread toward the surface and eventually be released into the vacuum [2]. In porous materials, o-Ps is also emitted into cavities, and, mainly in subnanometricsized voids, its lifetime can be notably reduced by pickoff annihilation: the o-Ps positron can annihilate via 2γ decay with an electron of the surrounding cavity walls if a relative singlet state is realized [3]. This property is at the heart of the use of Ps as a probe for studying nanoscale structures in condensed matter. In fact, while 2γ annihilation in vacuum depends on the electron density at the positron position (the contact density [4]), pickoff processes depend on the electron density in the bulk around the cavity.Experimental data obtained with the positron annihilation lifetime spectroscopy technique, also in the presence of a magnetic field (via magnetic quenching), primarily concern pickoff annihilation with lifetimes as low as a few ns [5,6]. The contact density can be determined from fitting lifetime spectra [7]. In molecular solids, this quantity is usually found to be well below the vacuum value. It is of paramount importance to connect these measurable quantities with the properties of Ps in small cavities as a means to obtain information on pore dimensions and other material characteristics.To describe Ps inside small cavities, the most used models are based on the Tao-Eldrup approach [8][9][10][11], which relates pickoff annihilation rates to pore sizes by considering Ps as a single quantum particle. Consequently, these models cannot give information about contact density and are suitable only when cavities are much larger than twice the Ps Bohr radius α 0 ¼ 0.106 nm. Another family of models, more ...

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“…Refs. [14]- [16] for experimental results and physical models), and positron binding with intra-molecular annihilation.…”

Section: Introductionmentioning

confidence: 99%

The effects of positron binding and annihilation mechanisms in biomolecules on PET resolution

Pichl

Tachikawa²,

Buenker³

et al.

IEEE Symposium Conference Record Nuclear Science 2004.

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Abstract-The angular correlation distribution of electronpositron annihilation photons is presented for polar biological molecules, and the associated non-collinearity effect on resolution in positron emission tomography is discussed. The image resolution in PET is known to be limited by a number of factors such as radioactive decay statistics, attenuation, scatter or random coincidence of annihilation photons. This work deals with the resolution limits on the side of the measured system. Our calculated distribution of annihilation momentum belongs to the intrinsic resolution factors together with the positron range in biological tissue; the other factors are due to the interactions along the photon path from the tissue to the detector. Here we demonstrate that the angular distribution of annihilation trajectories is not necessarily gaussian, especially when the positron temporarily binds in a molecular dipole moment field before annihilation. The theoretical framework treats the electron and positron on the same footing by using the multi-reference single-and double-excitation configuration interaction algorithms applicable also to other bound-state systems. Our results form a subset of parameters relevant to the statistical image reconstruction algorithms, which may eventually increase the sensitivity of PET imaging in clinical setting.

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General trends of positronium pick-off annihilation in molecular substances

Cited by 30 publications

References 34 publications

Insignia of positronium–molecular interaction in polyamide membrane material

Insignia of positronium–molecular interaction in polyamide membrane material

Positronium Confinement in Small Cavities: A Two-Particle Model for the Lowering of Contact Density

The effects of positron binding and annihilation mechanisms in biomolecules on PET resolution

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