Effect of an aerosol deposition pattern in the lung on the counting efficiency of a large area germanium detector array

The Human Monitoring Laboratory has extended the use of sliced lungs containing planar sources to simulate heterogeneous radionuclide deposition patterns. This work examined two deposition patterns and their effect on the counting efficiency of low-energy photons. The results have shown that heterogenous distributions can be difficult to detect in some cases and can still lead to large uncertainties (up to a factor of 2.5) in the activity estimate, especially at low photon energies. At higher energies (∼60 keV), the effect of the heterogeneous distribution is greatly reduced and errors in the activity estimate reduced to ∼25%. The presence of a heterogenous distribution can be detected by comparing the ratio of the individual detector counts with the expected values obtained from measuring multiple lungs sets that contained a homogeneous distribution. The distributions tested in this paper were detectable (at 2 ρ) as heterogeneous by two of the four detectors in the counting array. (authors)