The University of Edinburgh Nuclear Physics group is one of the most diverse in the country, with interests at both extremes of scale in the Universe. On the smallest scales, the properties of nuclei may be understood in terms of the interactions between their constituent elementary particles, quarks and gluons, while the macroscopic evolution of the universe is directly related to the interactions between nuclei.
Much of the success of the Group has been underpinned through its ongoing programme of development of Silicon detector devices, which is conducted in collaboration with the commercial company Micron Semiconductors. The research techniques developed by the Group have also found application in Environmental Radiation Monitoring. Most recently, the Group has begun a programme of Dark Matter Research, joining the UK Dark Matter Consortium in a search for the first direct evidence of non-baryonic dark matter that is thought to make up most of the mass of the Universe
During the last decade, a new generation of telescopes has allowed for the observation of cosmic γ rays throughout the interstellar medium, providing a versatile tool for studies of nucleosynthesis in stellar environments. In particular, observations of characteristic γ rays, associated with the decay of 26Al, provided the first direct evidence of ongoing nucleosynthesis in our Galaxy.
The COMPTEL and, more recently, INTEGRAL satellite missions indicate that supernovae and Wolf-Rayet stars, massive stars that suffer significant mass loss through strong stellar winds, are the likely dominant astrophysical sources of 26Al. However, large uncertainties in the nuclear reactions responsible for the destruction of 26Al in such environments have hindered comparisons between astrophysical models and observational data. This PhD project will focus on significantly reducing such uncertainties through experimental studies of the 26mAl(p,γ)27Si and 26gAl(d,p)27Al reactions at the world-leading TRIUMF national laboratory, Vancouver, Canada, and the 26Al(n,p)26Mg and 26Al(n,α)23Na reactions at the neutron time-of-flight ( n_TOF) facility at CERN, Switzerland. These measurements represent key goals for experimental nuclear astrophysics as well as unique technical challenges.
The nucleosynthesis of elements beyond iron is dominated by the slow (s) and rapid (r) neutron capture processes. However, 32 stable, proton-rich nuclides between 74Se and 196Hg, known as the ‘p-nuclei’, cannot be formed during those processes. The favoured production mechanism for the ‘p-nuclei’ is known as the p process, where material is initially processed from the neutron-rich to proton-rich side of stability by a series of (γ,n) reactions. However, almost no experimental data exist on the rates of the reactions involved in the p process since measuring cross sections in the Gamow window for such reactions, even for stable isotopes, is extremely challenging.
This PhD project will focus on utilizing a new sensitive method, recently developed for measuring these challenging reactions, using the heavy-ion storage ring (ESR) and decelerated stable beams at the GSI laboratory, Darmstadt, Germany. Such innovative measurements will vastly improve the current knowledge of p process reaction rates and considerably aid in answering an outstanding puzzle in nuclear astrophysics relating to the observed massive overabundance of p-rich isotopes of Molybdenum and Ruthenium in the Galaxy that cannot be accounted for by present p-process calculations.
The 34Ar(a,p)37K reaction has been identified as a key waiting point in the reaction path that leads to thermonuclear X-ray bursts on the surface of a neutron star. The reaction has never been measured directly because no 34Ar beam is presently available (34Ar is an unstable nucleus with a 0.844 s half life). However, a time reversal study, i.e. investigating the 37K(p,a)34Ar and inferring the cross section for the direct reaction by means of the reciprocity theorem, is now feasible thanks to the availability of a 37K beam.The project will be carried out at overseas facilities (either TRIUMF, Vancouver or Texas A&M University, College Station, Texas).
The student will be expected to play a key role in the planning of the experiment, its setup and running and the subsequent data analysis. Familiarity with experimental techniques in Nuclear Physics as well as in Fortran programming language is desirable.
Non-explosive stellar evolution is maintained by thermonuclear reactions between (mostly) stable nuclei. As these reactions proceed by quantum tunnelling, their experimental investigation in terrestrial laboratories is severely hampered by extremely low cross sections. Often, the only possibility to measure such cross sections directly at the energies of astrophysical interest rests in carrying out measurements underground. LUNA (Laboratory Underground for Nuclear Astrophysics), under the Gran Sasso massif in Italy, is currently the only facility in the world were these measurements can be made.
The student working on this project will have the opportunity to be involved in all the stages required for the measurement of a key low-energy nuclear reaction, including target preparation, experiment setup, beam tuning, data taking, data analysis and interpretation. The project is offered to a student with a strong academic background, a high degree of independence, and the aspiration to work within an international collaboration. Good data analysis and programming skills are desirable.
X-ray bursts are among some of the most energetic explosions in the Universe. They are believed to take place in binary stellar systems and to be triggered by the runway of thermonuclear reactions on the surface of a compact, degenerate object such as a neutron stars. The project will focus on the experimental measurement of reaction cross-sections for key reactions of interest using the time-reverse approach. The investigations will be carried out at the ISACII facility in TRIUMF (Vancouver). The student will be expected to play a key role in the planning of the experiment, its setup and running and the subsequent data analysis. Familiarity with experimental techniques in Nuclear Physics as well as in Fortran programming language is desirable.
The 14O(a,p)17F reaction is one of the most important reaction for explosive hydrogen burning in stars as it governs the conditions for a breakout from the Hot-CNO cycle, leading to the synthesis of elements up to the Sn region. Despite various direct and indirect attempts at measuring the cross section for this reaction, considerable discrepancy still exists between different data sets. The project will involve the direct investigation of this reaction cross-section and will be carried out at the GANIL facility in France. The student will be expected to play a key role in the planning of the experiment, its setup and running and the subsequent data analysis. Familiarity with experimental techniques in Nuclear Physics as well as in Fortran programming language is desirable.
Core collapse supernovae are some of the most violent explosions known, and present a truly extreme laboratory for doing nuclear physics. Our understanding of the mechanism by which they explode is limited by the complexity of the processes occurring. An exciting possibility for progress lies in satellites searching for gamma rays emitted by the explosion. In particular, gamma rays of a certain energy would tell us about the amount of 44Ti produced in the explosion, which in turn will reveal unique information about the hydrodynamics occurring deep within the thermonuclear explosion. In this work, we will use, for the first time, 44Ti reclaimed from previously irradiated material,and perform new experiments at the ISOLDE facility, CERN.
Astronomical evidence strongly suggests that the baryonic matter (the neutrons, protons, electrons etc of everyday material) contribute only some 4% to the mass of the Universe. The rest is composed of dark energy and dark matter. Direct detection of dark matter would both allow this view to be confirmed, and provide a route to new fundamental particle physics. The LUX project, based at the Homestake Mine in South Dakota, will be one of the world's leading projects in this highly exciting area.
As with any composite system (e.g atomic, nuclear) the excitation spectrum contains fundamental information on the dynamics and interactions of its components. The nucleon is a composite system comprised of three light quarks existing in a sea of gluons and quark-antiquark pairs. Around 98% of the mass of the nucleon (and therefore the visible universe!) is created by the energy of these interactions so study of the excitation spectrum of the nucleon is crucial to test our understanding of nucleon structure and the origin of mass generation. The PhD project will provide first accurate measurements of polarisation observables in meson photoproduction from the nucleon, a leading experiment in the current world programme to establish the excitation spectrum with accuracy for the first time. Currently the poor knowlege of this spectrum is a major issue in nuclear and hadron physics and it's current study is very timely given the recent advances in theoretical predictions from Lattice QCD, constituent quark models and higher dimensional theories based on string theory. These approaches give many contradictory predictions for the spectrum.
The experiment will be based at the Jefferson Laboratory in the USA (http://www.jlab.org) which is located on the east coast ~2.5 hours south of Washington D.C. The project will exploit the newly developed HD polarised nucleon and deuteron target with the CLAS spectrometer. There are also possible projects at the MAMI facility in Mainz (http://www.kph.uni-mainz.de)
In recent years theoretical and computational developments have made possible a direct link between the underlying theory of the strong interaction (QCD) and bound light quark systems for the first time. This opens up a rich hunting ground to not only test QCD as providing the detailed theory to describe the confinement processes but also to hunt for exotic beasts of QCD, which are predicted by the theory but remain unobserved. The existence, spectrum and nature of these particles are a fundamental test of QCD. The list include glueballs (particles made entirely from gluons) and hybrid mesons (in which the excited gluonic field inside the meson contributes to the meson's quantum numbers).
Our group is leading a major new experimental proposal which will run as the first experiment following the energy upgrade of Jefferson Lab (http://www.jlab.org) in the USA. We will construct new apparatus to detect electrons scattered at very small angles from the electron beam. Coincident reaction products from the interaction of the electron beam in the target will be detected using the new CLAS12 spectrometer. We have shown that our experiment has discovery potential for these exotic beasts of QCD. The PhD project will be to the execution of this experiment and analysis of the new data.
Heavy nuclei contain many more neutrons than protons. It has long been proposed that the neutrons form a skin on the surface of the heavy nuclei. We recently obtained data using a novel technique (coherent neutral meson photoproduction) which has established the existence of a neutron skin in heavy nuclei with world leading accuracy. This was done for a single nucleus (208Pb). The data provided a big improvement in the constraints on the density dependence of the asymmetry energy of nuclear matter. This has direct implications for the mass-radii relationship in neutron stars, structure of neutron stars and even rules out some proposed cooling mechanisms for heavy neutron stars. The next stage of this experiment has been approved to run in 2012 and will involve measurement of the development of a neutron skin across an isotopic chain of nuclei. The way the neutron skin develops as additional neutrons are added gives further precise information on the energetics of neutron rich matter. The experiment will take place at the MAMI facility in Mainz, Germany (http://www.kph.uni-mainz.de).
