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EP/J003980/1 - Positronium - Matter Interactions

Research Perspectives grant details from EPSRC portfolio

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Professor G Laricchia EP/J003980/1 - Positronium - Matter Interactions

Principal Investigator - Physics and Astronomy, University College London

Scheme

Standard Research

Research Areas

Antihydrogen Antihydrogen

Start Date

09/2011

End Date

08/2014

Value

£468,305

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Grant Description

Summary and Description of the grant

The observed imbalance between matter and antimatter in our universe is one of the greatest mysteries in science. Positrons are the antimatter counterpart to electrons with which they annihilate releasing gamma-rays. In addition to their importance in our fundamental understanding of nature, studies of their interactions with ordinary everyday matter allow us, for example, to investigate crystal structures and to obtain functional images of human organs using the medical technique of positron emission tomography (PET). In many collisions of positrons with matter, positronium (Ps) is formed.

Positronium is a composite made of a positron and electron, analogous to the hydrogen atom with the positron replacing the proton. So often is Ps formed, that e.g. 80% of gamma-rays detected in PET, and 95% of all gamma-rays released from the galactic centre of the Milky Way are the result of Ps decay. Once formed, it has ample time to interact with matter before annihilating because its lifetime, although of the order of nanoseconds, is still millions of times longer than typical scattering times. For these reasons, knowledge of how Ps itself interacts with matter is important not only for collision physics but also, for example, so that we may improve radioprotection in PET, or learn about the environment in which positrons annihilate in outer space.

Since both experimental and theoretical studies with Ps projectiles are difficult, corresponding data are scarce or non-existent. Recently, however, we have discovered that positronium scatters from a wide variety of atomic and molecular targets in a similar manner to that of a bare electron at a given projectile velocity. This is not what was expected! And, whilst the reason is unclear, its ramifications at a fundamental and practical level might be far reaching. It looks like the positron in Ps is heavily screened (or "cloaked") from the target by its partner electron and we wish to understand why. In the process, through the proposed research, we shall charter the outcome of such collisions and glimpse into the formation of Ps resonances and possibly Ps compounds. From a practical viewpoint, the outcome of the project may feed directly into models of how Ps interacts with matter, encompassing interstellar clouds and the human body.

Structured Data / Microdata


Grant Event Details:
Name: Positronium - Matter Interactions - EP/J003980/1
Start Date: 2011-09-01T00:00:00+00:00
End Date: 2014-08-31T00:00:00+00:00

Organization: University College London

Description: The observed imbalance between matter and antimatter in our universe is one of the greatest mysteries in science. Positrons are the antimatter counterpart to electrons with which they annihilate releasing gamma-rays. In addition to their importance in our ...