title: Levels of naturally occurring gamma radiation measured in British homes and their prediction in particular residences.
abstract: Gamma radiation from natural sources (including directly ionising cosmic rays) is an important component of background radiation. In the present paper, indoor measurements of naturally occurring gamma rays that were undertaken as part of the UK Childhood Cancer Study are summarised, and it is shown that these are broadly compatible with an earlier UK National Survey. The distribution of indoor gamma-ray dose rates in Great Britain is approximately normal with mean 96 nGy/h and standard deviation 23 nGy/h. Directly ionising cosmic rays contribute about one-third of the total. The expanded dataset allows a more detailed description than previously of indoor gamma-ray exposures and in particular their geographical variation. Various strategies for predicting indoor natural background gamma-ray dose rates were explored. In the first of these, a geostatistical model was fitted, which assumes an underlying geologically determined spatial variation, superimposed on which is a Gaussian stochastic process with Matérn correlation structure that models the observed tendency of dose rates in neighbouring houses to correlate. In the second approach, a number of dose-rate interpolation measures were first derived, based on averages over geologically or administratively defined areas or using distance-weighted averages of measurements at nearest-neighbour points. Linear regression was then used to derive an optimal linear combination of these interpolation measures. The predictive performances of the two models were compared via cross-validation, using a randomly selected 70 % of the data to fit the models and the remaining 30 % to test them. The mean square error (MSE) of the linear-regression model was lower than that of the Gaussian-Matérn model (MSE 378 and 411, respectively). The predictive performance of the two candidate models was also evaluated via simulation; the OLS model performs significantly better than the Gaussian-Matérn model.
authors.affiliation: Cancer Epidemiology Unit, University of Oxford, Richard Doll Building, Old Road Campus, Headington, Oxford, OX3 7LF, UK. Gerald.Kendall@ceu.ox.ac.uk.
authors.forename: G M
authors.identifier: http://orcid.org/0000-0002-9195-754X
authors.initials: GM
authors.lastname: Kendall
authors.affiliation: Centre for Occupational and Environmental Health, Institute of Population Health, The University of Manchester, Ellen Wilkinson Building, Oxford Road, Manchester, M13 9PL, UK.
authors.forename: R
authors.initials: R
authors.lastname: Wakeford
authors.affiliation: Bodleian Library, University of Oxford, Broad Street, Oxford, OX1 3BG, UK.
authors.forename: M
authors.initials: M
authors.lastname: Athanson
authors.affiliation: Childhood Cancer Research Group, University of Oxford, New Richards Building, Old Road, Oxford, UK.
authors.forename: T J
authors.initials: TJ
authors.lastname: Vincent
authors.affiliation: Earth Heritage Trust, Geological Records Centre, University of Worcester, Henwick Grove, Worcester, WR2 6AJ, UK.
authors.forename: E J
authors.initials: EJ
authors.lastname: Carter
authors.affiliation: Centre for Radiation, Chemical and Environmental Hazards, Public Health England, Chilton, Didcot, Oxon, OX11 0RQ, UK.
authors.forename: N P
authors.initials: NP
authors.lastname: McColl
authors.affiliation: Radiation Epidemiology Branch, Division of Cancer Epidemiology and Genetics, National Cancer Institute, DHHS, NIH, Bethesda, MD, 20892-9778, USA.
authors.forename: M P
authors.initials: MP
authors.lastname: Little
mesh_terms: D001417:Background Radiation; D005720:Gamma Rays; D005844:Geology; D006798:Housing; D016018:Least-Squares Analysis; D016013:Likelihood Functions; D016014:Linear Models; D011834:Radiation Monitoring; D011795:Surveys and Questionnaires; D006113:United Kingdom
keywords: Childhood cancer; Gamma radiation; Leukaemia; Natural background radiation