title: Fukushima Daiichi reactor source term attribution using cesium isotope ratios from contaminated environmental samples.
abstract: BACKGROUND
  Source term attribution of environmental contamination following the Fukushima Daiichi Nuclear Power Plant (FDNPP) disaster is complicated by a large number of possible similar emission source terms (e.g. FDNPP reactor cores 1-3 and spent fuel ponds 1-4). Cesium isotopic analyses can be utilized to discriminate between environmental contamination from different FDNPP source terms and, if samples are sufficiently temporally resolved, potentially provide insights into the extent of reactor core damage at a given time.
  
  
  METHODS
  Rice, soil, mushroom, and soybean samples taken 100-250 km from the FDNPP site were dissolved using microwave digestion. Radiocesium was extracted and purified using two sequential ammonium molybdophosphate-polyacrylonitrile columns, following which (135)Cs/(137) Cs isotope ratios were measured using thermal ionization mass spectrometry (TIMS). Results were compared with data reported previously from locations to the northwest of FDNPP and 30 km to the south of FDNPP.
  
  
  RESULTS
  (135)Cs/(137)Cs isotope ratios from samples 100-250 km to the southwest of the FDNPP site show a consistent value of 0.376 ± 0.008. (135)Cs/(137)Cs versus (134)Cs/(137)Cs correlation plots suggest that radiocesium to the southwest is derived from a mixture of FDNPP reactor cores 1, 2, and 3. Conclusions from the cesium isotopic data are in agreement with those derived independently based upon the event chronology combined with meteorological conditions at the time of the disaster.
  
  
  CONCLUSIONS
  Cesium isotopic analyses provide a powerful tool for source term discrimination of environmental radiocesium contamination at the FDNPP site. For higher precision source term attribution and forensic determination of the FDNPP core conditions based upon cesium, analyses of a larger number of samples from locations to the north and south of the FDNPP site (particularly time-resolved air filter samples) are needed.
authors.affiliation: Idaho National Laboratory, PO Box 1625, Idaho Falls, ID, 83415-2805, USA.
authors.forename: Mathew S
authors.initials: MS
authors.lastname: Snow
authors.affiliation: Idaho National Laboratory, PO Box 1625, Idaho Falls, ID, 83415-2805, USA.
authors.forename: Darin C
authors.initials: DC
authors.lastname: Snyder
authors.affiliation: Idaho National Laboratory, PO Box 1625, Idaho Falls, ID, 83415-2805, USA.
authors.forename: James E
authors.initials: JE
authors.lastname: Delmore
mesh_terms: D000363:Agaricales / Q000737:chemistry; D002588:Cesium Radioisotopes / Q000737:chemistry*; D062406:Fukushima Nuclear Accident; D012275:Oryza / Q000737:chemistry; D012990:Soil Pollutants, Radioactive / Q000032:analysis*; D013025:Glycine max / Q000737:chemistry
chemical_list: D002588:Cesium Radioisotopes; D012990:Soil Pollutants, Radioactive