New gamma-ray detector to search for fundamental structure of matter
UK physicists are constructing a novel, highly sensitive detector to create and probe rare and exotic types of atomic nuclei. The Advanced Gamma Tracking Array (AGATA) will be a thousand times more sensitive than previous detectors and will not only give physicists a new approach to uncovering the structure of the atomic nucleus but will help in the advancement of medical gamma-ray technology, used in hospital scans.
Atomic nuclei make up most of the visible matter in the Universe, including ourselves, so unlocking their structures is of great significance in not only understanding how the forces of nature work but also how the elements were created. By probing the structure of rare exotic atomic nuclei, with significant or extreme ratios of protons to neutrons, we may reveal why certain proton-neutron combinations are more stable than others, or have particular shapes. It may also shed light on how the elements are built up in stars, thought to happen via processes involving nuclei that are unusually rich in neutrons or protons. Another goal is to make massive nuclei with as many protons as possible in pursuit of discovering new super-heavy elements.
The social and economic benefits of AGATA include improved gamma-ray technology for PET and SPECT scanners - medical imaging and diagnosis machines which produce three-dimensional images of people’s bodies to provide information about localised function in internal organs and detect disease and tumors. Work is already in hand to develop portable radiation monitors based on AGATA technology, which could be used by the security services to detect dirty bombs, and also to monitor radioactive waste.
Professor Keith Mason, Chief Executive of STFC said, “This project is an exciting new step on our journey to uncover the structure of matter. It’s also a prime example of how fundamental research can have great economic and social impact on our everyday lives.”
Detecting gamma-rays from just a handful of transient exotic nuclei requires a new level of highly sophisticated spectroscopic instrumentation. AGATA, is being built by more than 40 partners from 12 countries. UK nuclear physicists have pioneered the development of gamma-ray spectrometers, and teams from The Science and Technology Facilities Council’s Daresbury Laboratory and the Universities of Liverpool, Manchester, Surrey, West of Scotland and York are taking a leading role in the development of this new and unique detector.
"The UK is responsible for the overall design and is heavily involved in the generation of the electronic digital data acquisition system," says John Simpson, from STFC's Daresbury Laboratory, the AGATA project manager.'
Like previous gamma-ray detectors, AGATA collects the gamma rays emitted when the nuclei decay, or when they are excited into a higher energy state by a laser or a collision with another particle. However, it differs from previous detectors in that the germanium detectors – a spherical, segmented array of germanium crystals, each about the size of baked-bean can - fill up the entire sphere, which dramatically improves the sensitivity.
The paths of the gamma rays, as they bounce around inside the detector, can be reconstructed using state-of-the-art computer methods. This enables the researchers to record both the position and energies of all the gamma rays reaching the detector. The characteristic spectrum of gamma-ray energies reveals much about the energy levels in the nuclei, the arrangement of protons and neutrons, and the overall shape of the nucleus.
STFC has recently announced its support to UK groups for the first operating phase, where the spectrometer will be built up to cover a quarter of the total solid angle. To maximize the science output of AGATA, campaigns of experiments of typically 15 months duration, with complementary research programmes will be pursued at accelerator research facilities within Europe. The first scientific campaign will start next year at Legnaro National Laboratory in Italy. The Ganil laboratory in France and the GSI facility in Germany will also host AGATA.
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Page last updated: 30 October 2008
by Julia Short
