Activity Concentration of Radon, Thoron, and Their Decay Products in an Open System

The article presents a model for the simulation of changes over time in the activity concentrations of radon and thoron and their progeny in an open system. The results of these simulations can be helpful in adapting the calibration process to the object in which it is to be carried out and the calibrated devices. In such cases, the critical quantities are the volume of the object, the air flow rate, and the corresponding filtration efficiency in the devices. All these parameters were included in the differential equations, and their solutions indicate the extent to which nuclide concentrations may change during device operation, especially in small-volume objects. Moreover, especially in the case of thoron, this nuclide should be continuously supplied to the calibration chamber, which ensures greater stability during the experiment. The equations also consider the possibility of a constant supply of nuclides and the removal of nuclides from the object, which also allows the use of this model in flow-through chambers.