AGATA: Precision Spectroscopy of Exotic Nuclei

The structure of the atomic nuclei, i.e. how protons and neutrons arrange themselves and how they interact among each other to form complex nuclei, has a decisive impact on everyday life, from the very existence of carbon-based life on Earth to critical nuclear physics applications such as carbon dating. Our understanding of nuclear structure is still elusive and relies on sophisticated experiments that deliver critical observables of atomic nuclei. For example, our experiments use particle accelerators that collide nuclei travelling at up to 50% the speed of light on stationary material to induce nuclear reactions. Typically, fewer than one in a million reactions will create the nucleus under study and the states of interest live, typically for less than a billionth of a second. To detect such rare events and measure the properties we are after, we need to develop very sensitive instruments.

This project supports the development of one of the most sensitive "microscopes", the AGATA spectrometer, for gamma rays that are emitted during the accelerator-induced nuclear reactions. These gamma rays carry critical information about what happened during the (violent) nuclear reaction. By studying the energy and direction of the gamma rays, we can extract the properties of the atomic nuclei that were involved in the collisions. Our results will help address critical questions in modern nuclear science.

AGATA constitutes a dramatic advance in gamma-ray detection that has wide ranging applications in medical imaging, astrophysics, nuclear safeguards and radioactive-waste monitoring, as well as introducing new detection capability for nuclear-structure studies. Indeed, the instrumentation and technical advances driven by this work and the knowledge gained by those involved will be important in a wide range of applications, such as in medicine and industry. For example, in medical imaging, reconstruction of the gamma-ray energies and determination of their direction will result in vastly improved images. Another beneficiary will be in nuclear safeguards where one of the big problems is the identification of the range of isotopes in waste and the determination of their quantities.

The impact of the UK project will derive from the signal processing and technological advances delivered to the next phase of the AGATA spectrometer. This impact will be enabled through the partnerships with industrial collaborators, major outreach projects, and will impact on other scientific disciplines outside nuclear physics. The innovative gamma-ray imaging technology developed will continue to lead to many collaborative projects for nuclear physics in the medical, security, decommissioning and environmental monitoring areas. The groups have a strong track record of industrial collaboration with partners including AWE, Kromek, the Defence Academy of the United Kingdom, Mirion Technologies (Canberra), Ametek (Ortec), John Caunt Scientific, National Nuclear Laboratory and Rapiscan. There have been many collaborative projects (for example NuPNET, DEPICT, GRi+, ProSPECTus, PorGamRays, PGRIS and GammaKeV), a number of which directly derive from earlier work pioneered within the AGATA collaboration. STFC has helped to leverage funds from these partners with support provided through the STFC CLASP, STFC mini-IPS, STFC follow-on, STFC IPS and STFC CASE schemes.

The technologies and techniques developed through the AGATA project have had and will continue to influence other disciplines. Examples include
The Pulse Shape Analysis and characterisation methods for HPGe signals are crucial for the success of background rejection in two large scale neutrinoless double-beta decay experiments, GERDA and MAJORANA which have recently merged to form the LEGEND collaboration. Moreover, realistic electric field calculations and signal generation algorithms are essential for an effective pulse-shape analysis and offer significant linkages between the AGATA project and these experiments.
Gamma-ray tracking algorithms are also used in Compton gamma cameras, which find applications in nuclear astrophysics, nuclear security, nuclear decontamination and decommissioning, and medical imaging.
The need for highly-segmented, position sensitive HPGe crystals imposed by the AGATA and GRETA arrays has enabled the vendor and industrial partner (Mirion Technologies) to develop the necessary detector technology to high standards.
In each of these areas there are significant opportunities to exploit the advances that will be enabled by the UK AGATA project. For the LEGEND collaboration, Liverpool are the UK lead for the next generation "inverted coax" detector characterisation programme which with output from the AGATA project grant will enable a new level of background reduction to be achieved. The gamma-ray tracking Compton Camera systems rely on high performance signal decomposition and tracking algorithms. The realisation of an automated approach to optimising these algorithms would open a huge range of opportunities. Finally pushing detector manufacturers industrialise high-segmented gamma-ray detector systems will in time lead to such systems being available for wider commercial application.

We will build on our excellent track record in public engagement and outreach to fulfil the important role of educating the public in nuclear radiation and its wider aspects. York have pioneered the 'binding blocks' nuclear-physics outreach project, with support from STFC. This allows members of the public and schools to build a 9m long 3D nuclear chart of all isotopes made completely out of Lego. We will continue this engagement, highlighting the areas of the chart that will be explored using AGATA. The groups engage widely with school pupils and teachers via several events, such as the year-12 nuclear-physics masterclasses, which have been hosted already by three of the institutions on this project. Events such as these will be used to highlight the innovation and scientific exploitation of the AGATA programme.