Research in CAMS
Research in CAMS falls into three main areas, outlined below. For more technical detail, see the Research section of the website.
Fundamental physics
One focus of CAMS activities will be the investigation of fundamental physics with positrons. By this, we mean investigating the interactions of positrons with atoms and molecules in a way that gives us insight into their behaviour at a quantum mechanical level. Despite that fact that quantum mechanics has been around for a long time, and is a well established theory, the interactions of charged particles, such as positrons, with single atoms is notoriously difficult to model correctly. This has to do with the nature of quantum mechanics itself — despite that fact that equations governing these interactions can be written down, they are impossible to solve analytically. Instead, numerous approximations have to be made to describe the interactions and a lot of computing power is needed to solve the equations numerically. Work such as this has been underway for electron interactions for a long time, but positrons present a different set of challenges as different interactions may take place, in particular the formation of positronium. The facilities of CAMS will allow the experimental investigation of these interactions at an unprecedented level of accuracy. In addition, CAMS includes some of the best theorists in the world in this area. By combining experiments with a new theoretical understanding, we plan to greatly increase our understanding of the interactions of positrons and matter at a fundamental level.
Materials science
Despite their exotic nature, positrons have a place in practical pursuits as well. In particular, they are becoming a useful tool in the analysis of material structure in certain situations. When positrons are injected into a material, they tend to drift towards any open volumes — very small holes. This is because they like to be away from the positive charge of the fixed nuclei in the material — like charges repel. When it finds a hole in the material, there are no electrons to annihilate with, so the size of the hole determines how long the positron lives. By looking at the lifetime of the positrons in the material, we can get information about the size and distribution of holes, or defects, that are about 1 nanometre in size. Holes of this size are related to important properties in some materials, such as porosity and conductivity. They can also be an early indicator of material degradation. In CAMS we plan to use one of the positron beamlines for the study of materials for various applications, from new plastics to silicon wafers to novel drug delivery devices for medical treatments.
Biological sciences
PET scans have become the tool of choice for imaging brain functions and certain types of cancers. This is done by injecting a positron emitting radio-isotope into the patient and looking at where the annihilation gamma rays are coming from. Despite the fact that this is a well established diagnostic tool, there is little understanding of what happens between the positrons being emitted from the isotope and annihilating. Usually the positrons come out with a high energy and need to slow down before meeting with an electron and producing the gamma rays. We plan to use the tools available in CAMS to study the interaction of positrons with bio-molecules and try and shed light on what happens between positron emission and positron annihilation. In particular, we want to look at ways in which the efficiency of the process might be improved.
