1. V. N. Nijampurkar, H. B. Clausen, Tellus, 42B (1990) 29
2. R. L. Patterson, Jr, L. B. Lockhart, Jr. Geographical distribution of lead-210 (RaD) in the ground-level air, in: The Natural Radiation Environment,J. Adams, W. Lowder (Eds), The University of Chicago Press Chicago, IL, 1964, p. 383.
3. I. H. Blifford, L. B. Lockhart, Jr., On the Natural Radioactivity of the Air, Report 4036, Naval Research Laboratory, Washington, D.C., 1952.
4. S. E. Poet, H. E. Moore, E. A. Martell, J. Geophys. Res., 77 (1972) 6515.
5. W. C. Graustein, K. K. Turekian, J. Geophys. Res., 91 (1986) 14355.