Topic
Positronium
About: Positronium is a research topic. Over the lifetime, 3895 publications have been published within this topic receiving 58571 citations. The topic is also known as: Ps.
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TL;DR: A balloon-borne germanium-gamma-ray telescope was used in this article to detect spectral features from the galactic center (GC) direction, and a 511 keV positron annihilation line was detected at a flux level of (1.22 +- 0.22) x 10/sup -3/ photons s/sup 1/ cm/sup 2.
Abstract: A balloon-borne germanium ..gamma..-ray telescope was flown over Alice Springs, Australia, in an attempt to detect spectral features from the galactic center (GC) direction. A 511 keV positron annihilation line was detected at a flux level of (1.22 +- 0.22) x 10/sup -3/ photons s/sup -1/ cm/sup -2/. Suggestive evidence for the detection of the three-photon positronium (ps) continuum is presented. A brief discussion of the possible origin of the positrons is given.
243 citations
TL;DR: In this paper, an extension of a simple quantum mechanical model of positronium annihilation in a pore adequately accounts for the temperature and pore size dependence of the Ps lifetime for pore sizes in the range from 0.1 nm to 600 nm.
Abstract: Depth-profiled positronium lifetime spectroscopy is used to probe the pore characteristics (size, distribution, and interconnectivity) in porous, low-dielectric silica films. The technique is sensitive to the entire void volume, both interconnected and isolated, even if the film is buried beneath a metal or oxide layer. Our extension of a simple quantum mechanical model of Ps annihilation in a pore adequately accounts for the temperature and pore size dependence of the Ps lifetime for pore sizes in the range from 0.1 nm to 600 nm. It is applicable to any porous media.
238 citations
TL;DR: It is found that when intense positron bursts are implanted into a thin film of porous silica, Ps2 is created on the internal pore surfaces much more efficiently than the competing process of spin exchange quenching, which appears to be suppressed in the confined pore geometry.
Abstract: It has been known for many years that an electron and its antiparticle, the positron, may together form a metastable hydrogen-like atom, known as positronium or Ps (ref. 1). In 1946, Wheeler speculated that two Ps atoms may combine to form the di-positronium molecule (Ps2), with a binding energy of 0.4 eV. More recently, this molecule has been studied theoretically; however, because Ps has a short lifetime and it is difficult to obtain low-energy positrons in large numbers, Ps2 has not previously been observed unambiguously. Here we show that when intense positron bursts are implanted into a thin film of porous silica, Ps2 is created on the internal pore surfaces. We found that molecule formation occurs much more efficiently than the competing process of spin exchange quenching, which appears to be suppressed in the confined pore geometry. This result experimentally confirms the existence of the Ps2 molecule and paves the way for further multi-positronium work. Using similar techniques, but with a more intense positron source, we expect to increase the Ps density to the point where many thousands of atoms interact and can undergo a phase transition to form a Bose-Einstein condensate. As a purely leptonic, macroscopic quantum matter-antimatter system this would be of interest in its own right, but it would also represent a milestone on the path to produce an annihilation gamma-ray laser.
223 citations
TL;DR: Positron annihilation spectroscopy (PAS) is a novel method that provides molecular-level information about complex macromolecular structure in a manner different from, but complementary to, conventional physical and chemical methodology as mentioned in this paper.
Abstract: Positron annihilation spectroscopy (PAS) is a novel method that provides molecular-level information about complex macromolecular structure in a manner different from, but complementary to, conventional physical and chemical methodology. This paper presents a perspective of PAS in polymeric systems covering 12 aspects: historical, spacial, spherical quantum model, anisotropic structure, voids, positronium chemistry, time, positron annihilation lifetime spectroscopy and data analysis, variable monoenergetic slow positron beam techniques and depth profiling, elemental analysis, multidimensional instrumentation advances in PAS, and free volume and free-volume theories.
208 citations
TL;DR: In this article, the positron affinity is defined as the sum of the Fermi level and the bottom of the lowest positron band relative to a common, well-defined reference energy.
Abstract: The relevant quantity in the comparison of the absolute positron energy levels in different materials is the sum of the internal electron and positron chemical potentials, i.e. the sum of the Fermi level and the bottom of the lowest positron band relative to a common, well-defined reference energy. This sum is defined as the positron affinity. The positron affinity reflects the preference of the positron for different components in heterostructures made of different materials and the preference between the host matrix and precipitates in alloys. Moreover, the affinity is closely related to the positron work function and positronium formation potential which are important parameters in the slow-positron-beam experiments. The authors have determined the positron affinity for the alkaline and alkaline-earth metals, 3d-, 4d-, and 5d-transition metal series, and for some metals on the right in the Periodic Table. The diamond structure semiconductors are also considered. The determination is based on the self-consistent electron structure calculations and the subsequent calculation of the positron band structure within the local-density approximation. The trends are studied and interpreted along the different columns and rows of the Periodic Table. The results are also compared with available experiments.
203 citations