Birmingham Nuclear Physics Consolidated Grant 2016

Lead Research Organisation: University of Birmingham
Department Name: School of Physics and Astronomy


Our proposed research has three broad themes that build upon our world leading areas of expertise.

The first of these involves the study of high-energy nuclear collisions at the Large Hadron Collider, the world's highest energy particle accelerator. The aim of the ALICE experiment is to study nuclear matter, as it would have existed about a millionth of a second after the Big Bang when the Universe was so hot and so dense that nuclei did not exist. In its primordial state nuclear matter consists of its fundamental constituents (quarks and gluons) in a plasma state. We recreate this novel state of matter in our experiment and we are developing ways of studying these high-energy nuclear collisions to discover the properties of the quark-gluon plasma. This is technically challenging and the group has developed a sophisticated electronic trigger system that controls the experiment. The quark-gluon plasma has remarkable properties, such as an abundance of strange quarks and near-perfect fluidity. In this proposal, we are trying to determine whether size matters by finding the smallest drop of plasma that still retains these properties. We are using grazing collisions to explore the internal structure of nuclei at high energy. And we are looking at the debris of quarks and gluons that are sometimes scattered out of the collision, producing a shower of particles in our detector known as a jet, to study the conditions inside the plasma. We are also performing R&D into new detector technologies based on silicon pixel detectors in which the readout electronics is contained within the pixel.

The second strand extends beyond the quark scale to the scale of nuclei. Here the challenge is to understand how the nature of the strong interaction plays out on the nuclear, rather than the sub-nucleon scale. Here the strong force is highly complex, which is manifest in correlations. These can be pairing correlations or correlations of higher order, which results in the formation of alpha-particle clusters. The geometric arrangement of clusters produces dynamical symmetries, which in turn gives a fingerprint of quantum mechanical states. The work performed by the Birmingham group has indicated the presence of a triangular arrangement of alpha particles in 12C. We propose to extend the techniques and ideas to a study of 16O that is predicted to be strongly influenced by a tetrahedral structure. What happens to alpha-particle clustering as particles are either added or removed from the cluster cores is extremely important as this is intimately connected with the structure of nuclei at the drip-lines. We will be studying a number of systems that will provide a deeper insight into phenomena such as nuclear molecules. Finally, we plan to develop an experimental programme to exploit gamma-ray beams to probe with great precision the structure of clustered nuclei via their electromagnetic properties. To-date this tool has provided us with some of the best insights into the structure of light nuclei and we plan to extend these studies to exotic cluster states above the cluster decay threshold. This programme will produce measurements to constrain state-of-the-art theory.

This grant also recognises the importance of applying nuclear physics knowledge through a variety of applications. In the field of energy production using both nuclear fission and fusion there is a need for more precise measurements of a variety of nuclear reactions. We plan to use the University of Birmingham's MC40 cyclotron for nuclear data studies. Moreover, the cyclotron may be used to create a high radiation environment that mimics either reactor or decommissioning environments. We will develop a facility that will be used to test instrumentation and detection systems for use in such environments.

Planned Impact

There are three areas of impact related to this proposal: knowledge exchange and industrial engagement, public understanding of science and outreach.

The Birmingham Nuclear Physics Group will seek to maximise impact from its two nationally leading facilities: the MC40 cyclotron and the Positron Imaging Centre. This will build upon the group's role in the Birmingham Centre for Nuclear Education and Research, which is a focal point for industrial engagement with the nuclear industry. This is already paying dividends through investment in robotics research for nuclear decommissioning and by virtue of the training we provide to a new generation of nuclear engineers through undergraduate and postgraduate courses that we have developed. During this grant we will develop a pan European training network in collaboration with the European Commission's Joint Research Centre. We will continue to develop flipped learning packages building on already successful materials produced for EDF and the Royal Society of Chemistry. Through some of the applications proposed in this grant there is an opportunity to perform measurements of nuclear reactions critical to the development of advanced materials for fusion and fission energy applications. There is scope to establish the cyclotron as a national facility for these type of measurements. Furthermore, we are working to bring our expertise in radiation detection and measurement to bear on the problem of large area radiation monitoring, relevant to nuclear decommissioning. The Positron Imaging Centre has developed the technique of Positron Emission Particle Tracking, important for understanding industrial mixing processes. There is scope to expand this capability, using the MC40 cyclotron to make the required radioactive tracers. Similarly, some of the electronics developments that we are carrying out for the upgrade of the ALICE experiment may have wider impact. The proposed hardware developments related to MAPS sensors may have applications to medical physics as well as being relevant for a number of future projects in nuclear and particle physics.

A second strand revolves around the public understanding of science. The research that is outlined in this proposal has the potential to capture the imagination and to inspire a new generation of scientists. One part of the proposed research programme is involved in studying nuclear matter as it would have existed a fraction of a second after the Big Bang. This aspect is relevant to evolution of the early universe. The other focuses on the Hoyle state in 12C, responsible for the synthesis of carbon in stars. Understanding the structure of the Hoyle state is a challenge that is relevant not only to nuclear science but also the origins of carbon-based life itself. The group has a excellent track record in bringing its work to the awareness of the general public. We will continue to do this in the next grant period with the aspiration to inform and to educate.

Finally, the group has an extensive outreach programme, interacting with local schools and regional science centres and hosting events at the University. In the last grant period we developed and hosted a Nuclear Physics Masterclass for Y11 school students. We are committed to repeating this on an annual basis.


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Description 1. We have demonstrated that hadrons containing strange quarks are enhanced in high multiplicity proton-proton and proton-lead collisions at the LHC. Strangeness enhancement has long been believed to be a signature of quark-gluon plasma formation in heavy-ion collision. Observing similar enhancements in smaller systems suggest that quark-gluon plasma formation may be a general feature of high energy collisions at the LHC.
2. Baryons containing two or three strange quarks are particularly sensitive to strangeness enhancement. Our studies have shown that the enhancement of these types of particles is a function only of the event multiplicity and independent of the collision system or collision energy. This appears to confirm the previous finding, suggesting that the strangeness enhancement depends most strongly on the size of the final system and not how it was made.
3. Ultra-peripheral collisions are grazing collisions with minimal overlap between the opposing beams. This type of collision is senstive to the internal quark (and gluon) structure of nuclei, in ways that direct nuclear collisions are not. Particle production process are driven by photo-nuclear reactions where the cross sections are sensitive to the gluon density in the nucleus. Ultra-peripheral proton-lead and lead-lead collisions have been studied to look for evidence of gluon saturation in nuclei. Our results favour theoretical models incorporating moderate gluon shadowing illustrating the importance of quantum interference effects in nuclei.
4. In high energy nuclear collisions, quarks and gluons can be scattered out of the colliding beams materialising as high energy jets of hadrons. Jets provide a novel way of exploring the properties of hot nuclear matter created in these collisions. This work has explored how the internal structure of jets is modified by the hot nuclear medium through which they pass. We showed that jets with a well-defined two-prong cluster structure can be used to probe colour-screening effects in the quark-gluon plasma, providing new insight into the mechanism of medium-induced jet quenching. We also showed that jet energy-loss (or jet quenching) is sensitive to the opening angle of two-pronged jets, measuring the ability of the medium to resolve the internal structure of the jet.
5. The novel application of machine learning algorithms to identifying clustering in complex medium mass nuclei has been demonstrated. This goes hand-in-hand with a new technique of using the wavelet transform on experimental spectra from thick-target resonant scattering in inverse kinematics. This is the first time the wavelet transform has been applied in this field and the results demonstrate (for the first time) that titanium-52 exhibits clustering of the form: calcium-48 + alpha. This result is important for understanding nucleosynthesis in stars and can be applied to many more medium-mass systems.
6. Following conflicting reports of nuclear clustering in the literature for the oxygen-18 system, the Birmingham group have led a systematic study of this system. This comprehensive investigation has established the decay properties of a large number of states (>50) in oxygen-18 up to 16 MeV and established that all but a few exhibit no strong cluster structure. This resulted from using a method to measure the decay properties of states in a novel kinematically complete way to capture all decay paths in one investigation. This includes decays via neutral particles that are often omitted due to the difficulty in detecting them. These results are relevant to stellar burning processes and nucleosynthesis as the lack of clustering means there is no significant enhancement in the alpha reaction channels leading to this nucleus.
7. A new gamma simulator has been developed and used to generate training data for a machine learning model to rapidly and accurately identify radioactive isotopes using low-statistics spectra from a range of shielding scenarios. This use of a convolutional neutral network (CNN) results have been verified by comparing to experimental data. This work has demonstrated the accuracy and speed improvements that can be made using machine learning in this challenging area which has many applications.
Exploitation Route This work will be taken forward in LHC Run 3 with an upgraded ALICE detector, starting in 2022. The work on jets and ultra-peripheral collisions is relevant for studies of proton and nuclear structure at a future electron-ion collider (EIC) that is under construction in the United States and expected to come into operation in the early 2030s.
Sectors Education

Description The the gamma simulator and machine learning (Convolutional Neural Network - CNN) for radio-isotope identification (RIID) is part of an industrially funded project between AWE, University of Birmingham and CCFE UKAEA. This has resulted in demonstration of a CNN for improving speed and accuracy and has many potential applications in the areas of radiation monitoring and security. Additionally, the simulator and associated tools from this project have been used during the COVID19 pandemic; forming the basis of an Online Virtual Nuclear Laboratory (O-LAB) developed at Birmingham which benefited, in 2020, over a 120 students in it's first roll out. The group at Birmingham plans to further develop this into an open source that can be used for engagement activities as well as teaching.
Sector Aerospace, Defence and Marine,Education,Energy
Impact Types Economic