Inversion of the Jacobi-Porstendörfer room model for the radon progeny

The Jacobi room model, describing the behaviour of free and attached radon progeny in the atmosphere of a room was introduced by W. Jacobi 37 years ago [1], was worked out and broadly applied in indoor measuring by J. Porstendorfer [4, 5]. It has been successfully used up to now without substantial changes, so designating it as the J-P model is justified. There have been several attempts to invert measured data to determine the parameters describing the physical processes by approximate approaches [2, 3]. Here, an exact solution is given.