A variety of sensor types have been operated in electron bombarded mode, including CCDs CMOS sensors, and silicon sensors (pixellated photodiodes) in conjunction with active pixel sensors (e.g. Medipix [2]). This project aims to develop a photon counting capability for the TDCpix [3], a newly developed pixel sensor with exceptional timing resolution. It follows on from a previous PIPSS and BBSRC-funded collaboration with CERN to develop a multi-channel photon-counting detectors with picosecond event timing for life science applications. Our original IPS project utilized a microchannel plate detector with CERN-developed preamplifier and time-to-digital ASICs. The recent development of the TDCpix active pixel sensor by the same group at CERN offers comparable time resolution (100 ps binning, and electronic resolution ~30ps) but with a much higher pixel count (40 x 45 pixels, 12 x 13.5mm^2)), a much higher level of miniaturization provided by integration of the entire electronics on to the chip, and a greatly increased overall count rate capability of ~130 Mcount/s per ASIC, an order of magnitude higher per unit area than its microchannel plate based predecessor. An electron bombarded TDCpix would offer unrivalled performance with commercial potential for applications using time-correlated single photon counting (TCSPC) such as high content cell screening and other expanding fields in the life science sector, LIDAR instruments for remote sensing, and a variety of other event timing applications where only small arrays of individual photomultiplier tubes are the norm. Our aim in this project is to identify and develop a technology for photon counting detectors using electron bombarded silicon devices, in order to remove the active pixel sensor from within the vacuum tube, thus greatly simplifying design, de-risking the manufacturing process, and enhancing performance. Removing the chip from the tube will eliminate undesirable elements such as high density vacuum electrical feedthroughs, materials with poor vacuum compatibility, and internal bump, wire, and chip bonding, and will lift the restrictions imposed by these on tube processing which impact manufacturing yield, device reliability, and ultimately, sensor lifetime. Given a successful outcome to this project, we intend to propose a follow-on IPS project, one of whose goals would be to incorporate an additional, relatively low (x20) gain stage using a linear mode electron avalanche process within each pixel of the silicon sensor, matched to the requirements of electron bombarded operation. This will allow the electron bombardment gain to be lowered, reducing the tube operating voltage to safer levels, and reducing the lifetime-threatening radiation damage. The other elements of an electron bombarded detector design, the vacuum tube including photocathode, and the silicon sensor, will be provided by our industrial collaborators; Photek Ltd., and Micron Semiconductor Ltd, respectively. Photek have extensive experience of design and manufacture of custom vacuum-based detectors with specific expertise in the electron bombarded mode devices, having manufactured an electron bombarded Medipix-based detector. Micron Semiconductor have substantial experience and heritage producing large quantities of custom pixellated silicon sensors for harsh radiation environments at CERN LHC and other similar experiments. Specifically for this project, they have developed a thin entrance window technology which is highly desirable for electron bombarded mode to minimize photoelectron energy loss. The thickness of their currently available Type-9.5 window is 500 Angstroms, and a Type-10 window is under development with a thickness goal of 200 Angstroms. Micron also have a bump-bonding capability necessary for the interconnect development.

After surgery, radiation treatments are the most widely used and successful way to cure cancers. However, modern radiotherapy plans often cause severe side-effects to the patient and the overall success rate is still only moderate. Therefore there is a need to research new ways of delivering radiotherapies in order to inform and improve new treatments in the future.Radiotherapy works by killing cancer cells - usually by breaking the DNA in those cells. If the damage is so severe that the cells cannot repair it, the cells die. A lot of the research into radiotherapy is aimed at understanding how cells respond to radiations of different types and doses.One reason why radiotherapy results in side-effects is because healthy cells are damaged, or killed, as well as cancerous ones. Therefore considerable efforts have been made to minimize these effects and to focus the destructive power of radiation on tumour cells. This has been achieved, to some extent, with X-rays by irradiating the patient from multiple external sites. An alternative, and very promising, approach is the use of ion beams in place of x-rays. There are already numerous proton treatment facilities worldwide (including one in the UK) and centres using heavier ions (eg carbon) are now being brought into operation.The big advantage of ion beams is due to the way they deposit their energy in tissue. When an X-ray beam enters a person, energy is deposited immediately upon entry, thus causing damage. In contrast, ion beams can pass several centimeters through tissue before depositing the bulk of their energy. By manipulation of the physical properties of the ion beam, the depth at which ion beams deposit their energy can be controlled and made to correspond to the site of the tumour. Thus the bulk of this type of radiation's destructive power is concentrated in the cells which we wish to destroy. The results from ion beam irradiation are impressive, with improved clear-up rates and decreased side-effects.A further improvement on ion beams, may be to use antiprotons. Antiprotons will be familiar to any reader of science fiction - usually as the means of propulsion of interstellar starships or in a fearsome and destructive weapons systems. However, antiprotons can be produced here on earth, contained, controlled and used in experiments. Like their regular matter counterparts, protons, they can pass through material for several centimeters before depositing their energy. Their potential advantage arises from the fact that when an antiproton meets a proton, the two particles annihilate each other (according to Einstein's famous equation E=mc2) releasing lots of energy.A group of scientists at the European Centre for Nuclear Research (CERN) in Switzerland have begun experiments to see if antiprotons can be used in cancer therapies. This group (the ACE collaboration) have shown that antiprotons kill cells approximately four time better than protons. However, before antiprotons can be considered a viable possibility in cancer radiotherapy, considerable extra scientific work is required.In 2008, the applicants joined the ACE collaboration and carried out an experiment at CERN to investigate the effects of antiprotons on cultured human cells. They showed that antiprotons cause damage to the DNA in these cells and that the more antiprotons the cells are exposed to, the more DNA damage is caused. In addition, they demonstrated that media from irradiated cells can cause DNA damage responses in non-irradiated cells. This phenomenon, the so-called bystander effect, is well documented with other types of radiation, but has not previously been shown with antiproton irradiation.The applicants now seek funding to return to CERN in autumn 2009, in order to continue these experiments. This year they hope to learn more about the bystander effect resulting from antiproton irradiation, including quantifying the magnitude of these effects.

Abstracts are not currently available in GtR for all funded research. This is normally because the abstract was not required at the time of proposal submission, but may be because it included sensitive information such as personal details.

Antihydrogen was the first, and so far the only, atom made entirely of antimatter to be produced. In 2002 two teams of scientists independently produced the first cold antimatter atoms at the European centre for nuclear physics, CERN. Antihydrogen is neutral, and is therefore relatively unperturbed by electric and magnetic fields. Measurements on antihydrogen can therefore, in principle, reach the highest level of precision of any man-made measurements via spectroscopic comparison with its normal matter counterpart hydrogen. This comparison is intended to help explain the antimatter/matter asymmetry in the Universe. The current standard model of particle physics, and the underlying quantum theories, imply that there is perfect symmetry between matter and antimatter. This symmetry means that when energy is transformed into matter (following Einstein's famous equation E=mc^2) / exactly equal amounts of matter and antimatter will be formed. However, the Universe of today seems not to contain significant amounts of antimatter, in particular is there no evidence of antimatter stars or planets, nor that the so-called dark-matter should be antimatter. Thus, to put it popularly, we currently miss 50% of the Universe. The research into antimatter, which this project is all about, aims to help resolve this mystery.An important step towards precision comparison of antihydrogen and hydrogen, is to trap the neutral antihydrogen. (Anti)hydrogen can only be trapped in a magnetic trap, which is very shallow, only allowing trapping of atoms with temperatures below about one degree above absolute zero. This means that it is not enough to just make the antihydrogen cold, it has to be very cold. The aim of this project is exactly that; make very cold antihydrogen and trap it. Antihydrogen is normally made by merging plasmas of its constituents: antielectrons (positrons) and antiprotons. In earlier work by the principal investigator and others it was found that up until now, the somewhat brute-force approach used makes antihydrogen which is significantly warmer than the surroundings. So, even with cryogenic surroundings at four degrees above absolute zero, very few trappable antiatoms would be produced. In this project a range of plasma physics techniques will be implemented. These techniques offer detailed control over the shape and density of the plasmas, as well as diagnostics for these parameters. Although the techniques have been applied elsewhere, the challenge here is to make them into work horses in the complex experimental setup that is used for antihydrogen formation. Furthermore, the techniques have not been applied to the extent proposed here in multi-species plasmas. Using these techniques, it is expected that detailed control of the antihydrogen internal states and their temperature can be obtained. These two parameters are both crucial for the success of magnetic trapping, and the future goal of antihydrogen spectroscopy.

The observation that the particulate Universe is currently comprised mostly of matter seems unequivocal, as does the assertion that at its birth, the Universe contained equal amounts of matter and antimatter. Just why this imbalance, or asymmetry, has evolved is currently not understood, and indeed it is one of the central questions of physics beyond what is known as the Standard Model. The conventional approach to experimentally explore symmetry in fundamental physics is to study particle collisions at ever-higher kinetic energies, in an effort to reproduce conditions further back towards the beginning of the Universe (the Big Bang). It is becoming increasingly clear, though, that such investigations can be complemented and enriched via small scale experiments, for instance in setting limits on particle electric dipole moments, with novel dark matter searches and, as here, in precision comparisons of the properties of matter and antimatter. We have chosen to bring the powerful toolbox developed via the physics of atom trapping and cooling and atomic spectroscopy to bear on this problem. In short, we create, capture and then cool antihydrogen atoms before studying their properties and behaviour. In one set of experiments (ALPHA-III, which will be devoted to spectroscopic investigations) we intend to systematically probe the transition between the ground state of the anti-atom and its first excited state using a technique known as two-photon Doppler-free spectroscopy. We hope to determine its frequency with a precision similar to that currently achieved for the hydrogen atom, for which it is known to a staggering 14 decimal places. This will deliver a very direct test of symmetry. We have already measured the same transition in antihydrogen to 12 decimal places and we are now aiming for the hydrogen precision. Additionally, we intend to determine fundamental constants in anti-atoms, such as the anti-Rydberg constant and the antiproton charge radius, by combining the ground-to-first excited state work with spectroscopic measurements of additional transitions. In our second major experimental avenue, so-called ALPHA-g, we will analyse the trajectories of antihydrogen atoms as they leave a purpose-built atom trap whose magnetic fields have been carefully tailored to enhance experimental sensitivity to the gravitational behaviour of the anti-atom. We expect to make the first determination of the acceleration of antimatter due to gravity. Eventually we hope to extract the value of g for antihydrogen to an accuracy of 1% or better. Interest in the behaviour of gravity on (anti-)atomic systems stems in part from another puzzle of modern physics, namely that our theory of gravity (Einstein's General Relativity) is incompatible with currently accepted quantum field theories. And whilst the equivalence principle dictates that all objects, irrespective of their content (e.g., in this context independently of whether they are comprised of matter or antimatter), should fall with the same acceleration towards the Earth, testing the (classical) theory of gravity on quantum objects is of fundamental interest. Electrically neutral antimatter-systems are preferable, since they are immune to the influence of electric fields, which can swamp the effects of gravity for charged particles, and antihydrogen is particularly suitable, since it can now be trapped and cooled. Thus, our two-pronged attack on symmetry and gravity by exploring the physics of antihydrogen promises the development of new insights into nature. Our ability to pin down the properties and behaviour of anti-objects is unprecedented, and we aim to further develop this with the work set out in this proposal. Any difference between matter and antimatter, however small, will have profound consequences for our understanding of physics and the laws of nature.