[en] The estimation of the internal exposure of Uranium workers is usually based on urine measurements and in- vivo measurement by lung counters. Another important parameter is the solubility class of the Uranium aerosols which were inhaled and the intake date. The accuracy of estimation of these parameters influences the overall error in the estimation of the internal exposure. The average MDA - Minimum Detectable Activity for natural uranium of the NRCN lung counter system is 50 Bq, for 40 minutes counting time. The MDA is a function of the system efficiency, background and counting time. For a given system, the efficiency and background are constant, and the only variable parameter is the counting time. Due to human psychological limitations we can't exceed a practical counting time of 40-60 minute for a specific measurement. Because of this limitation, the MDA may not be sufficient for comparison with intake evaluations assessed from the urine results. An obvious, practical and simple method is proposed to improve the MDA for lung counting results : summing of several accumulated spectra. Results are presented for three workers, which where measured 9 times, at a intervals of two days, each measurement performed for 40 minutes. By combining the 9 measurements we obtain an overall counting time of 360 minutes and improve the MDA by a factor of 3. The significance for the inner exposure determination is discussed