title: Indoor terrestrial gamma dose rate mapping in France: a case study using two different geostatistical models.
abstract: Terrestrial gamma dose rates show important spatial variations in France. Previous studies resulted in maps of arithmetic means of indoor terrestrial gamma dose rates by "departement" (French district). However, numerous areas could not be characterized due to the lack of data. The aim of our work was to obtain more precise estimates of the spatial variability of indoor terrestrial gamma dose rates in France by using a more recent and complete data base and geostatistics. The study was based on the exploitation of 97,595 measurements results distributed in 17,404 locations covering all of France. Measurements were done by the Institute for Radioprotection and Nuclear Safety (IRSN) using RPL (Radio Photo Luminescent) dosimeters, exposed during several months between years 2011 and 2012 in French dentist surgeries and veterinary clinics. The data used came from dosimeters which were not exposed to anthropic sources. After removing the cosmic rays contribution in order to study only the telluric gamma radiation, it was decided to work with the arithmetic means of the time-series measurements, weighted by the time-exposure of the dosimeters, for each location. The values varied between 13 and 349 nSv/h, with an arithmetic mean of 76 nSv/h. The observed statistical distribution of the gamma dose rates was skewed to the right. Firstly, ordinary kriging was performed in order to predict the gamma dose rate on cells of 1*1 km(2), all over the domain. The second step of the study was to use an auxiliary variable in estimates. The IRSN achieved in 2010 a classification of the French geological formations, characterizing their uranium potential on the bases of geology and local measurement results of rocks uranium content. This information is georeferenced in a map at the scale 1:1,000,000. The geological uranium potential (GUP) was classified in 5 qualitative categories. As telluric gamma rays mostly come from the progenies of the (238)Uranium series present in rocks, this information, which is exhaustive throughout France, could help in estimating the telluric gamma dose rates. Such an approach is possible using multivariate geostatistics and cokriging. Multi-collocated cokriging has been performed on 1*1 km(2) cells over the domain. This model used gamma dose rate measurement results and GUP classes. Our results provide useful information on the variability of the natural terrestrial gamma radiation in France ('natural background') and exposure data for epidemiological studies and risk assessment from low dose chronic exposures.
authors.affiliation: Institut de Radioprotection et de Sûreté Nucléaire, Bureau d'étude et d'expertise sur la radioactivité naturelle, IRSN, PRP-DGE, SEDRAN, BRN. BP17, 92262 Fontenay aux Roses, Cedex, France; Mines ParisTech, Centre de Géosciences, Equipe de Géostatistique, 35 rue Saint Honoré, 77305 Fontainebleau, France. Electronic address: eric.warnery@irsn.fr.
authors.forename: E
authors.initials: E
authors.lastname: Warnery
authors.affiliation: Institut de Radioprotection et de Sûreté Nucléaire, Bureau d'étude et d'expertise sur la radioactivité naturelle, IRSN, PRP-DGE, SEDRAN, BRN. BP17, 92262 Fontenay aux Roses, Cedex, France. Electronic address: geraldine.ielsch@irsn.fr.
authors.forename: G
authors.initials: G
authors.lastname: Ielsch
authors.affiliation: Mines ParisTech, Centre de Géosciences, Equipe de Géostatistique, 35 rue Saint Honoré, 77305 Fontainebleau, France. Electronic address: Christian.Lajaunie@mines-paristech.fr.
authors.forename: C
authors.initials: C
authors.lastname: Lajaunie
authors.affiliation: Institut de Radioprotection et de Sûreté Nucléaire, Laboratoire de Dosimétrie de l'IRSN. IRSN/LDI. 31 rue de l'Ecluse, 78 294 Croissy Sur Seine Cedex, France. Electronic address: eric.cale@irsn.fr.
authors.forename: E
authors.initials: E
authors.lastname: Cale
authors.affiliation: Mines ParisTech, Centre de Géosciences, Equipe de Géostatistique, 35 rue Saint Honoré, 77305 Fontainebleau, France. Electronic address: hans.wackernagel@mines-paristech.fr.
authors.forename: H
authors.initials: H
authors.lastname: Wackernagel
authors.affiliation: Institut de Radioprotection et de Sûreté Nucléaire, Laboratoire de surveillance atmosphérique et d'alerte IRSN, PRP-ENV, SESURE, LS2A. BP 40035, 31 rue de l'écluse, 78116 Le Vésinet Cedex, France. Electronic address: christophe.debayle@irsn.fr.
authors.forename: C
authors.initials: C
authors.lastname: Debayle
authors.affiliation: Institut de Radioprotection et de Sûreté Nucléaire, Bureau d'étude et d'expertise sur la radioactivité naturelle, IRSN, PRP-DGE, SEDRAN, BRN. BP17, 92262 Fontenay aux Roses, Cedex, France. Electronic address: jerome.guillevic@irsn.fr.
authors.forename: J
authors.initials: J
authors.lastname: Guillevic
mesh_terms: D005602:France; D005720:Gamma Rays; D011834:Radiation Monitoring / Q000379:methods*
keywords: France; Gamma dose rate; Geology; Geostatistics; Mapping; Uranium