1. Departament de Matemàtiques, Universitat Autònoma de Barcelona, 08193 Bellaterra (Barcelona), Spain
2. Public Health England, Centre for Radiation, Chemical and Environmental Hazards, Chilton, Didcot, Oxon OX11 0RQ, UK
3. BCAM—Basque Center for Applied Mathematics, 48009 Bilbao, Spain
4. Institute of Health and Society, Newcastle University, Newcastle upon Tyne NE1 4LP, UK