Estimation of low level Carbon-14 in the environment, 2

Rice grains harvested recently at thirty Agricultural Experiment Stations located in nation wide scale in Japan were provided and their C-14 contents were estimated by a Methanol-LSC method. Rice grains are baked firstly to yield charcoal. Carbon dioxide produced by combustion of the charcoal is allowed to react with LiAlH4 suspended in diethyl carbitol followed by alcoholysis with n-butyl carbitol to give methanol. The crude methanol is purified with a fractional distillation to yield pure methanol as a sample for liquid scintillation counting (LSC). Specific activities of the sample methanol are measured in an energy range of 19 - 156 KeV with a Tri-Carb 460 CD Liquid Scintillation Counter. In this work, the duplicated results obtained on rice grains provided from each district are consistent extremely with each other within experimental errors. The average C-14 concentration of rice grains harvested in various districts of Japan in the fall of 1982 was found to be 16.68 ± 0.17 dpm/gC. (author)