Predictive model for the 14C radioactivity in a plant following an exposure to airborne 14CO2 gas

This paper provides details of a dynamic compartment model for estimating the 14C radioactivity in an agricultural plant exposed to an amount of airborne 14CO2 gas. The plant, in the model, is divided into two compartments, the plant body (shoot and root) and ears, to predict the radioactivity of different parts of a plant. The carbon transports from, to and between the compartments are described by the processes of a photosynthesis, respiration, and translocation. The carbon transport fluxes of these processes are determined from the growth rates of a plant, which are usually easily attained. The model predictions showed that the present model could converge to a region where the specific activity model is applicable when the elapsed exposure time was extended up to the harvest time of a plant. The 14C activity of a plant was greatly affected by the elapsed exposure time, the developmental stages of a plant at an exposure time, and the airborne 14C activity during an exposure. It was expected that the peak of the ears' 14C activity appeared when the exposure time was close to the ears-maturity date. The model predictions agreed reasonably well with the measured 14C radioactivity of the rice plants that were artificially exposed to 14CO2 of a high 14C source for a short period of time in an exposure box.