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First measurements of the differential positronium-formation cross-sections

Positrons are the antimatter version of electrons and so their fate in a matter world is ultimately to annihilate. However, prior to this, a positron may combine with an electron to form a matter-antimatter hybrid called positronium. This is akin to a hydrogen atom with the proton replaced by a positron. Fundamental to our understanding of the physical universe, positron and positronium are these days also acknowledged as being fantastically useful in practical applications such as probing material properties and medical diagnostics. However, there is still much that we do not know for sure about the details of the interactions of these particles with ordinary matter. For example if, in a collision with an atom or molecule, a positron captures an electron, in which directions is the positronium likely to travel and with what probability? More...

Published: Jun 17, 2015 12:35:19 PM

CO2 Satellite

New calculations to improve carbon dioxide monitoring from space

How light of different colours is absorbed by carbon dioxide (CO2) can now be accurately predicted using new calculations developed by a UCL-led team of scientists. This will help climate scientists studying Earth’s greenhouse gas emissions to better interpret data collected from satellites and ground stations measuring CO2. More...

Published: Jun 15, 2015 10:29:10 AM

Watt Steam Engine

On quantum scales, there are many second laws of thermodynamics

New research from UCL has uncovered additional second laws of thermodynamics which complement the ordinary second law of thermodynamics, one of the most fundamental laws of nature. These new second laws are generally not noticeable except on very small scales, at which point, they become increasingly important. More...

Published: Feb 10, 2015 11:55:53 AM

Positron-, Positronium-, and Electron-Collisions

Prof Nella Laricchia and Prof Jonathan Tennyson

The study collisions of particles with molecular targets is a core research activity within the AMOPP group. These studies reveal important fundamental details of collision physics of electrons, positrons and positronium with  atoms, and small and large molecules.

Collisions of Positrons and Positronium with molecules (Prof Nella Laricchia and Prof Jonathan Tennyson)

Although still considered somewhat exotic particles, positrons (the antiparticles of electrons) and positronium (the bound state of an electron and a positron) are currently employed in the exploration of fundamental effects ranging from condensed matter physics to astrophysics as well as in the diagnostics of living biological systems and of the electronic and structural properties of industrially important materials.

Our main research interests are in atomic physics problems where beams of positrons and positronium with speeds comparable to those of atomic electrons are contributing to the unravelling of general collision phenomena as well as illuminating specific interactions and processes such as exchange and annihilation. Current hot topics of research worldwide include positron-induced ion production (comprising ionization with and without Ps formation, annihilation, etc), positron impact excitation (vibrational and electronic) and positronium scattering. Measurements of differential ionization and positronium collisions are in their infancy. UCL is a pioneer in this type of research. You can read more about our work here.
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Scattering of electrons from molecules (Prof Jonathan Tennyson)

rmat The molecular physics group studies the scattering of electrons from diatomic and polyatomic molecules using the R-matrix method. Applications include fusion plasma modelling (see with workshop on Electron-molecule Collision Data for Modelling and Simulation of Plasma Processing in 1998) and applications in astrophysics. Scattering cross-sections are computed as well as bound state energies of N+1 electron systems.

Our work uses the UK molecular R-matrix code. The figure to the left illustrates the principle of the R-method. You can read more about our work here.