Modelling chemical kinetics in 11 C gas target systems towards a generalized production equation

Gas target systems are the main tool for producing [${}^{11}C$]CH₄ or [${}^{11}C$]CO₂ for nuclear medicine. Modelling has suggested that adsorption to the target body walls plays an important role in the recoverable radioactive yield from a target system. Here, we build on a previous model describing adsorption by including the kinetics of intermediary chemical species. The model equations are presented and simplified to a tractable form, from which expressions for the saturation yield and the initial production rate are derived. The model agrees with experimental data from different target body materials, beam currents, and loading pressures. The model predicts that increasing chemical kinetic rates will increase the recoverable yield from a target. This is experimentally validated with a forced convection target which increases in-target gas mixing, favoring reaction kinetics over adsorption losses.