Abstract: Efficiency calibration is a key link in in vivo internal contamination monitoring of human body, and also is an important factor of the measurement accuracy. According to the CT images of the torso phantom, a three-dimensional voxel phantom is established. The Computational models of the HPGe detector is characterized by means of Monte Carlo transport codes, validated experimentally using point sources to verify the detector response at different energies and to further improve it with the inclusion of dead layers and inactive volumes on the crystals. A computer program is developed by Geant 4 to simulate the lung counter. By comparing on of the results of simulation and experimental results for lung counter detection efficiency of ²⁴¹Am, the differences are found as 2.47% (59.5 keV) and -8.58% (17.5 keV). Meanwhile a software was developed to solve the predicted values due to intake radionuclides by means of numerical solution of the ICRP biokinetics models. A case was studied on inhalation of class M ²⁴¹Am. It was analyzed how the other organs retentions influenced the efficiency calibration of lung counter. The results show that the whole body's efficiency is higher than the lung efficiency in the first two days and 50 days after intake ²⁴¹Am, and both efficiencies are more consistent in 3—50 days after intake ²⁴¹Am.

Key words: lung counter, efficiency calibration, voxel phantom, monte carlo, biokinetics models