Japanese Journal of Health Physics

Total depositions in a human tracheobronchial cast were measured for ultrafine monodisperse aerosols below 0.1μm in diameter at flow rate of 4, 10 and 20l/min of constant and cyclic flows. The cast model consisted of the trachea and bronchial airways with branching generations from 4 to 10. At 20l/min constant flow, the inspiratory deposition efficiencies were 5% and 44% for 0.1 and 0.00475μm size particles, respectively. The deposition efficiency increased with decreasing particle size and flow rate. Compared with the inspiratory deposition, the expiratory deposition efficiencies were slightly higher for particles below 0.01μm. The deposition efficiencies under cyclic flow were found to be almost the same as those under constant flow having equivalent mean flow rate. It was also observed that varying the tidal volume, but keeping the minute volume constant (i. e., having the same mean flow rate), has little effect on deposition of the ultrafine aerosol particles.

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Experimental methods for determining the counting efficiency of instruments that measure radon progeny concentration are proposed and described in this paper. For determining the counting efficiencies of ²¹⁸Po and ²¹⁴Po, alpha particles from radon progeny were first sampled from a radon-tank and deposited on the surface of a filter. These alpha particles were then alternately counted by two instruments; a standard instrument, S, with known counting efficiency, and an instrument, G, with unknown counting efficiency. Using the proporsed methods, the relative counting efficiency of ²¹⁸Po and ²¹⁴Po using instrument G was determined by comparing the indicated counting efficiency with the known counting efficiency of instrument S. In addition, measured radon progeny concentration data are shown that were calculated from the counting efficiencies obtained with this calibration procedure. These results show that it is important to accurately determine counting efficiencies because a small difference between the counting efficiencies of ²¹⁸Po and ²¹⁴Po may give relatively large differences between indicated concentrations of ²¹⁸Po, ²¹⁴Pb and ²¹⁴Bi.

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An international cooperative study named BIOMOVS has been carried out from 1986 under the auspices of the Swedish National Institute of Radiation Protection. The objective of this study is to validate models for estimating the transfer and bioaccumulation of radionuclides and stable trace substances in the biosphere. The Japan Atomic Energy Research Institute has participated in the study from the beginning. This report describes test scenarios and results for Phase I which was performed until 1990. The report also introduces suggested themes and prospects for Phase II started in 1992.

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