[en] A recently developed phantom was used to compare the X-ray detection efficiencies for ¹⁰³Pd and plutonium, present in the phantom's lungs, with efficiencies previously recorded for ¹⁰³Pd deposited in the lungs of volunteers, or derived for plutonium from those observations. Also values for the ratio R defined as the counts per K X-ray emitted by ¹⁰³Pd to the counts per L X-ray emitted by plutonium in the lungs were deduced and were compared to the values of R predicted by calculation. The results showed an encouraging similarity between the detection efficiencies for ¹⁰³Pd in the phantom and those recorded for ¹⁰³Pd in vivo, suggesting that the pulmonary distribution of activity in the experimental subjects was similar to that in the phantom, i.e. that it was essentially uniform. The further consistency between detection efficiencies for plutonium for the phantom and those derived from data on ¹⁰³Pd in vivo, together with the overall similarity between predicted and observed values of R has improved the confidence in these two quite different approaches to the problem of calibration. (U.K.)