Abstract: The invention relates to a method for determining the distance of a target in difficult industrial conditions, method in which (i) one of the gamma quanta produced from a radioactive source in annihilation and traveling in opposite directions is aimed at the target and the other one at a detector, which detects it, and time measuring starts; (ii) the quantum Compton-scattered from the target is detected by the same or a separate detector, and time measuring stops; (iii) the distance of the target is calculated from the time difference between (i) and (ii). The invention also relates to a device for carrying out the method, the device comprising a radioactive source, a scintillation crystal counter/counters, a time-amplitude converter (TAC) and a pulse height analyzer (PHA).