Evaluation for Committed Effective Dose Due to Dietary Foods by the Intake for Japanese Adults

Abstract

The 90 Sr and 137 Cs measurements were conducted by radio-chemical analysis. The ground ash samples were decomposed with aqua regia and nitric acid. Strontium was separated from other fission products and natural radioactive elements, which were removed with carbonate; however, cesium remained in the aqueous phase. Strontium was purified using a cation exchange resin column (Dowex, 50W-X8). The 90 Y, generated from 90 Sr, was scavenged with iron hydroxide. After radioactive equilibrium of 90 Sr and 90 Y had been maintained for two weeks, the 90 Y was precipitated as the iron hydroxide for counting using a low-background anti-coincidence beta counter (ALOKA, model LBC-471Q). Chemical yield was determined by inductively coupled plasma atomic emission spectrometry (SII Nano Technology Inc., model SPS7800). Cesium and other alkaline elements were separated from the supernatant solution after carbonate precipitation. The cesium was adsorbed by ammonium phosphomolybdate (AMP). The AMP was dissolved with sodium hydroxide. The solution was passed through a cation exchange resin column (Muromac, C-3) for purification and removal of K and Rb. The eluate was evaporated to dryness and dissolved with distilled water (Millipore, Milli-Q TM). The cesium was precipitated as cesium chloroplatinate with hexachloroplatinum acid. Radioactivity in the precipitate was counted using a low-background beta counter. The recovery yield of cesium was determined by weight. The concentrations of 238 U and 232 Th were determined by inductively coupled plasma mass spectrometry (Agilent Technologies, model 4500). The ground ash samples were decomposed with nitric acid and hydrogen peroxide. The solution was evaporated to dryness and the residue dissolved with nitric acid. The sample solution was diluted and bismuth was added to the solution as an internal standard (10 ng/mL). Radium 226 was determined by liquid scintillation spec-trometry as follows. Barium was added to the samples as a recovery indicator. The ground ash samples were decomposed with nitric acid and hydrofluoric acid. The solution was evaporated to dryness and the residue dissolved in hydrochloric acid. Radium was co-precipitated with barium sulfate [Ba(Ra)SO4] by adding sulfuric acid. The barium sulfate was purified by dissolution in ethylene diaminetetraacetic acid (EDTA) solution at pH 10. Then the sulfate was re-precipitated by acetic acid (pH 4.5). The sulfate precipitate was filtrated and weighed for determination of recovery. The sulfate precipitate was dissolved with phosphoric acid and placed into a Teflon TM vessel with a scintillation cocktail (toluene). After two weeks of growth, 226 Ra was determined by liquid scintil-lation counter (Aloka, model LSC LB-5). The 239 + 240 Pu level was determined by radiochemical analysis. A measured quantity of 242 Pu as a yield tracer was added to the ground ash sample. The sample was decomposed with nitric acid and hydrogen peroxide solution. After concentrating the sample solution, nitric acid and a sodium nitrate solution were added. The residue was removed by filtration and prepared for anion exchange. After undergoing anion exchange, the column was washed with nitric acid to remove U(VI), Fe, and Pb. The Th was removed with hydrochloric acid, and then Pu was eluted with ammonium iodine-hydrochloric acid solution. The eluted Pu fraction was evaporated to dryness. Nitric acid and perchloric acid were added and the solution evaporated to dryness. Finally, the sample was dissolved with sulfuric acid and Pu was electrodeposited on a stainless steel disk for measurement using an alpha ray spectrometer.