Edinburgh Nuclear Physics Group Consolidated Grant Proposal

Lead Research Organisation: University of Edinburgh
Department Name: Sch of Physics and Astronomy


The elements we see around us today are still being forged by nuclear reactions in stars and some were first produced as early the primordial big-bang. Understanding the different astrophysical origins and production mechanisms of the elements is a fundamental challenge in science. Remarkable new astronomical observations, including those of neutron star mergers by Gravitational Wave, and electromagnetic radiation measurements, provide a challenge to nuclear physics to determine the key nuclear properties required to understand and model element production at these astrophysical sites. In the case of neutron star mergers and the production of heavy elements beyond Iron, this involves explosive reactions on isotopes with 20-30 neutrons more than the stable isotopes we see around us today. Here on the earth we are now able to produce these exotic isotopes for the first time using modern heavy ion accelerators. The Edinburgh Group has led the development of a key detection system, AIDA, to perform these measurements on these isotopes as they begin their long decay journey back to stability. In a new development within the Group we will be using ion traps to momentarily incarcerate these exotic isotopes to precisely measure their masses, a fundamental property that determines how far from stability the production of heavy elements proceeds.

Heavy elements can also be produced over a long period of time by neutron fusion reactions during quiescent phases of stellar evolution, tracking closely to the line of stability. In this case, the reaction probabilities need to be measured directly in nuclear reaction measurements with intense neutron beams. The origin of the neutrons in stellar environments occurs by very low energy fusion reactions between charged particles and requires quantum tunnelling to proceed. These reactions have very low reaction probabilities and will be measured at a new underground accelerator facility LUNA MV where the background from cosmic rays is low. At the same facility, we will explore the reaction rate between Carbon nuclei that determines whether massive stars explode as supernovae or whither away into white dwarfs. We will measure a reaction occurring during core collapse supernovae explosions that controls the amount of gamma-rays observed from the subsequent decays of radioactive nuclei after the explosion using a storage ring where the radioactive ions repeatedly traverse a Helium gas target and the reactions are measured with a new detector system, CARME, developed by the Group. This system will also be used to measure reactions occurring in novae explosions that control the production of elements ejected into the cosmos and isotopic ratios measured in pre-solar grains found in meteorites. We will also explore the evolution of nuclear shell structures far from stability, including phenomena at magic numbers, representing particular stable quantum configurations. These structures leave behind their fingerprints in the abundances of the elements.

Finally we return to the original elemental origin, the Big Bang. Here astronomical observations, of the microwave background radiation and light element abundances, now supercede the precision of nuclear reaction measurements required to model the Big Bang so we will measure a key reaction for the Big Bang using CARME on the storage ring representing a completely new approach to such measurements, where we hope to improve the precision and eliminate certain systematic sources of error. Such improved measurements can for example limit the possible existence of exotic particles beyond the Standard Model of Particle Physics.

Planned Impact

The Group studies nuclear astrophysics in explosive stellar events and quiescent stellar burning, stellar modelling, and the structure of unstable nuclei. This programme is underpinned by innovative experimental techniques and particularly expertise in semiconductor radiation detectors instrumentation, low background measurements, mass spectrometry with ion traps, and advanced computer simulations.

Dr. Reiter is rapidly developing ion trap and mass spectrometry capabilities at our research laboratories in Edinburgh. He is exploring synergies with the Scottish Instrumentation and Resource Centre for Advanced Mass Spectrometry, a facility for ultra-high-resolution mass spectrometry based at the School of Chemistry. The centre provides one of the most advanced mass measurement facilities in Europe providing access to academic and industrial users from across the UK and the world. Currently the centre employs narrow-band, ultra-high-resolution and broadband, medium-resolution devices. The new Multiple-Reflection Time-Of-Flight (MR-TOF) technique, closes the gap between the existing experimental capabilities of the centre. The unique combination of MR-TOF performance characteristics (combining high resolving power, high precision, fast measurement speed, large ion handling capabilities, and large signal to background ratios) makes the technique ideally suited for mass measurements of very rare and short-lived isotopes. This opens up unique applications in analytic mass spectrometry including Isotope Ratio measurements. The isotopic profile is unique to the origin and history of a substance. Isotope Ratio Mass Spectrometry has a wide range of applications, ranging from forensic sciences (drug identification, environmental monitoring, etc), archaeology, geochemistry to biological sciences (toxicology, metabolic studies etc.) as outlined by the UK Forensic Isotope Ratio Mass Spectrometry Network. Commercial mass spectrometry companies have started the development of their own MR-TOF-MS devices indicating the wider impact and commercial potential of such device developments.

Nuclear energy can play an important role in addressing the world's increasing energy demands, if safety, waste and proliferation issues are satisfactorily addressed. Advances in the design of advanced systems such as Generation IV reactors (with full or partial waste recycling capabilities), or accelerator driven systems, as well as finding new fuel cycles require improvement in basic nuclear data, in particular cross-sections for neutron induced reactions on actinides. High accuracy neutron reaction measurements on actinides are performed at the n_TOF facility, CERN. Measurements on actinides include radiative neutron capture and neutron induced fission. The Group developed a silicon strip detection system to measure neutron-induced charged particle reactions. It was used to measure neutron induced reactions on 14N and 35Cl. Nitrogen and Chlorine are present in the human body and the 14N(n,p)14C and 35Cl(n,p)35S reactions are of key importance in the boron neutron capture therapy of cancer because the emitted protons deliver locally a significant tissue dose. Understanding the radiation risks imposed by such background reactions of neutrons is essential for developing NCT into a routine treatment.

Alex Murphy is co-leading the STFC Public Engagement Sparks award, Remote3: Remote sensing by Remote schools in Remote environments. The aim of this project is to bring STEM opportunities to pupils located in remote communities, for which the distance from urban centres presents a significant barrier to engagement with outreach opportunities.The research by the Group engages with the public's enthusiasm and interest for science at the largest and smallest scales. Members of the Group promote this public interest with a wide range of engagements and activities such as talks to schools public lectures, national print and radio media..