Critical parameters for the delay time of a RIB target

An investigation is made of the parameters that influence the delay time in a target and ion source system for the production of radioactive beams using a Monte Carlo method. The critical parameters are not known with any certainty, hence existing geometries may be far from optimum. This work models the target intended for use in the RIST experiment at RAL. The principal mechanisms for the delay of nuclei from their production within the foils to extraction from the ion source are diffusion from the target foil material and effusion within the target container. The main part of the Monte Carlo program consists of calculating the path lengths through the RIST target geometry. The diffusion constants and sticking times are used as a variable to fit the calculated delay curves to the experimental results gained from measurements at ISOLDE. This gives insight into which are the more dominant mechanisms, allows predictions to be made to optimise the target geometry and gives a measurement of the diffusion constants and sticking times.