For all sources of radioactivity, radiological risk assessments are essential for safeguarding human and environmental health. But assessments often have to rely upon simplistic assumptions, such as the use of simple ratios in risk calculations which combine many processes. This pragmatic approach has largely arisen due to the lack of scientific knowledge and/or data in key areas. The resultant uncertainty has been taken into account through conservative approaches to radiological risk assessment which may tend to overestimate risk. Uncertainty arises at all stages of the assessment process from the estimation of transfer to human foodstuffs and wildlife, exposure and risk. Reducing uncertainty is important as it relates directly to scientific credibility, which will always be open to challenge given the highly sensitive nature of radiological risk assessment in society. We propose an integrated, multi-disciplinary, programme to assess and reduce the uncertainty associated with radiological risk assessment to protect human health and the environment. At the same time we will contribute to building the capacity needed to ensure that the UK rebuilds and maintains expertise in environmental radioactivity into the future. Our project has four major and highly inter-related components to address the key goal of RATE to rebuild UK capacity and make a major contribution to enhancing environmental protection and safeguarding human health. The first component will study how the biological availability of radionuclides varies in soils over time. We will investigate if short-term measurements (collected in three year controlled experiments) can be used to predict the long-term availability of radionuclides in soils by testing our models in the Chernobyl exclusion zone. The second component will apply the concepts of 'phylogeny' and 'ionomics' to characterise radionuclide uptake by plants and other organisms. These approaches, and statistical modelling methods, are increasingly applied to describe uptake of a range of elements in plant nutrition, and we are pioneering their use for studying radionuclide uptake in other organisms and human foods. A particularly exciting aspect of the approach is the possibility to make predictions for any plant or animal. This is of great value as it is impossible to measure uptake for all wildlife, crops and farm animals. The third component of the work will extend our efforts to improve the quantification of radiation exposure and understanding of resultant biological effects by investigating the underlying mechanisms involved. A key aim is to see whether what we know from experiments on animals and plants in the laboratory is a good representation of what happens in the real world: some scientists believe that animals in the natural environment are more susceptible to radiation than laboratory animals: we need to test this to have confidence in our risk assessments. Together these studies will enable us to reduce and better quantify the uncertainties associated with radiological risk assessment. By training a cohort of PDRA and PhDs our fourth component will help to renew UK capacity in environmental radioactivity by providing trained, experienced researchers who are well networked within the UK and internationally through the contacts of the investigators. Our students will be trained in a wide range of essential skills through their controlled laboratory studies and working in contaminated environments. They will benefit from being a member of a multidisciplinary team and opportunities to take placements with our beneficiaries and extensive range of project partners. The outputs of the project will benefit governmental and non-governmental organisations with responsibility for assessing the risks to humans and wildlife posed by environmental radioactivity. It will also make a major contribution to improved scientific and public confidence in the outcomes of environmental safety assessments.

Aerosol science, the study of airborne particles from the nanometre to the millimetre scale, has been increasingly in the public consciousness in recent years, particularly due to the role played by aerosols in the transmission of COVID-19. Vaccines and medications for treating lung and systemic diseases can be delivered by aerosol inhalation, and aerosols are widely used in agricultural and consumer products. Aerosols are a key mediator of poor air quality and respiratory and cardiac health outcomes. Improving human health depends on insights from aerosol science on emission sources and transport, supported by standardised metrology. Similar challenges exist for understanding climate, with aerosol radiative forcing remaining uncertain. Furthermore, aerosol routes to the engineering and manufacture of new materials can provide greener, more sustainable alternatives to conventional approaches and offer routes to new high-performance materials that can sequester carbon dioxide. The physical science underpinning the diverse areas in which aerosols play a role is rarely taught at undergraduate level and the training of postgraduate research students (PGRs) has been fragmentary. This is a consequence of the challenges of fostering the intellectual agility demanded of a multidisciplinary subject in the context of any single academic discipline. To begin to address these challenges, we established the EPSRC Centre for Doctoral Training in Aerosol Science in 2019 (CDT2019). CDT2019 has trained 92 PGRs with 40% undertaking industry co-funded research projects, leveraged £7.9M from partners and universities based on an EPSRC investment of £6.9M, and broadened access to our unique training environment to over 400 partner employees and aligned students. CDT2019 revealed strong industrial and governmental demand for researchers in aerosol science. Our vision for CDT2024 is to deliver a CDT that 'meets user needs' and expands the reach and impact of our training and research in the cross-cutting EPSRC theme of Physical and Mathematical Sciences, specifically in areas where aerosol science is key. The Centre brings together an academic team from the Universities of Bristol (the hub), Bath, Birmingham, Cambridge, Hertfordshire, Manchester, Surrey and Imperial College London spanning science, engineering, medical, and health faculties. We will assemble a multidisciplinary team of supervisors with expertise in chemistry, physics, chemical and mechanical engineering, life and medical sciences, and environmental sciences, providing the broad perspective necessary to equip PGRs to address the challenges in aerosol science that fall at the boundaries between these disciplines. To meet user needs, we will devise and adopt an innovative Open CDT model. We will build on our collaboration of institutions and 80 industrial, public and third sector partners, working with affiliated academics and learned societies to widen global access to our training and catalyse transformative research, establishing the CDT as the leading global centre for excellence in aerosol science. Broadly, we will: (1) Train over 90 PGRs in the physical science of aerosols equipping 5 cohorts of graduates with the professional agility to tackle the technical challenges our partners are addressing; (2) Provide opportunities for Continuing Professional Development for partner employees, including a PhD by work-based, part-time study; (3) Deliver research for end-users through partner-funded PhDs with collaborating academics, accelerating knowledge exchange through PGR placements in partner workplaces; (4) Support the growth of an international network of partners working in aerosol science through focus meetings, conferences and training. Partners and academics will work together to deliver training to our cohorts, including in the areas of responsible innovation, entrepreneurship, policy, regulation, environmental sustainability and equality, diversity and inclusion.

Seismic hazard assessment and understanding of continental deformation are hindered by unexplained slip-rate fluctuations on faults, associated with (a) temporal clusters of damaging earthquakes lasting 100s to 1000s of years, and (b) longer-term fault quiescence lasting tens to hundreds of millennia. We propose a new unified hypothesis explaining both (a) and (b), involving stress interactions between fault/shear-zones and neighbouring fault/shear-zones; however key data to test this are lacking. We propose measurements and modelling to test our hypothesis, which have the potential to quantify the processes that control continental faulting and fluctuations in the rates of expected earthquake occurrence, with high societal impact. Our aspiration is that cities and critical facilities worldwide will gain additional protection from seismic hazard through use of the calculations we pioneer herein. The background is that slip-rate fluctuations hinder understanding because they introduce uncertainty about whether specific faults are active or not. For example, a review in Japan of earthquake risk to critical facilities, such as the Tsuruga nuclear power plant (NPP), revealed a geological fault under a nuclear reactor (Chapman et al. 2014). The question that arose was whether the fault was active or not. Japan's Nuclear Regulatory Authority (NRA) has guidelines defining fault activity, and considered the fault under the reactor to be active, evidenced by faulting in sediments <~125,000 years in age. The Japan Atomic Energy Power Company (JPAC) disagreed, following study by an independent team of geoscientists. In 2014, the Tsuruga NPP remained closed due to ongoing debate between the NRA and JPAC, with similar debates ongoing for other NPPs. We suggest that defining fault activity as simply "active" or "inactive" is unsatisfactory because it is debatable even amongst experts. In fact a fault that has not slipped in many millennia may, in reality, not be inactive, but instead may simply have a low slip-rate, with the capability to host a damaging earthquake after a long recurrence interval. Our breakthrough is we think slip-rate fluctuations over both timescales (a and b) are a continuum, sharing a common cause involving interaction between fault/shear-zones. For the first time, we provide calculations that describe this interaction, quantifying slip-rate fluctuations and seismic hazard in terms of probabilities. We show that slip during an earthquake cluster on a brittle fault in the upper crust occurs in tandem with high strain-rate on the viscous shear-zone underlying the fault. This deformation of the crust produces changes in differential stress on neighbouring fault/shear-zones. Viscous strain-rate is known to be proportional to differential stress, so, given data on slip-rate fluctuations one can calculate changes in differential stress, and then calculate implied changes to viscous strain-rates on receiver shear zones and slip-rates on their overlying brittle faults. We provide a quantified example covering several millennia, but lack data allowing a test over tens to hundreds of millennia. If we can verify our hypothesis over both timescales, through successful replication of measurements via modelling, we will have identified and quantified a hitherto unknown fundamental geological process. We will study the Athens region, Greece, where a special set of geological attributes allows us to measure and model slip-rate fluctuation over both time scales (a and b), the key data combination never achieved to date. We know of no other quantified explanation that links slip-rate fluctuations over the two timescales; the significance and impact of accomplishing this is that it has the potential to change the way we mitigate hazard for cities and critical facilities. Chapman et al. 2014, Active faults and nuclear power plants, EOS, 95, 4