UK physicists are constructing a novel, 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," said The Science and Technology Facilities Council (STFC).

Detecting gamma-rays from just a handful of transient exotic nuclei requires sophisticated spectroscopic instrumentation.

UK nuclear physicists have pioneered the development of gamma-ray spectrometers, claims STFC, with teams from STFC's Daresbury Laboratory and the Universities of Liverpool, Manchester, Surrey, West of Scotland and York taking a leading role in the development.

AGATA, is being built by more than 40 partners from 12 countries.

"The UK is responsible for the overall design and is heavily involved in the generation of the electronic digital data acquisition system," said AGATA project manager John Simpson, from the Daresbury Lab in Oxfordshire.

Like previous gamma-ray detectors, AGATA collects gamma rays emitted when nuclei decay, or when they are excited into a higher energy state by a laser or a collision with another particle.

It differs from previous detectors in that the germanium detectors fill up an entire sphere centred on the reaction site.

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The sphere is an array of 60 'hexaconical' and 12 'pentaconical' germanium crystals (grey in the diagram), each about the size of baked-bean can - 206kg of germanium in total, machined from 400kg of cylindrical ingots.

Behind each segment are pre-amplifiers and digital electronics. In the diagram, the electronics are yellow, support structure red, and the green parts are cryogenic Dewar flasks.

The paths of the gamma rays as they bounce around inside the detector will be reconstructed using computer. "This enables researchers to record both the position and energies of all the gamma rays reaching the detector," said STFC. "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 is to support UK groups for the first operating phase, where the spectrometer will be built up to cover a quarter of the total solid angle.

To maximise the science output of AGATA, campaigns of experiments of typically 15 months duration, with complementary research programmes, will be pursued at accelerator research facilities across Europe.

The first campaign will start next year at Legnaro National Laboratory in Italy, followed by the Ganil laboratory in France and the GSI facility in Germany.