1. Rundo, J., Brewster, D. R., Essling, M. A. and Sha, J. Y. Radioactivity in former workers at a thorium refinery. ANL Report No. UAC-42694 (Argonne National Laboratory, USA) (1979).
2. Terry, K. W. and Hewson, G. S. Thorium lung burdens of mineral sand workers. Health Phys.69(2), 233–242 (1995).
3. Mayya, Y. S., Prasad, S. K., Nambiar, P. P. V. J., Kotrappa, P. and Somasundaram, S. Measurement of Rn220 in exhaled breath of thorium plant workers. Health Phys.51(6), 737–744 (1986).
4. Mehta, D. J., Dang, H. S., Sharma, R. C. and Sunta, C. M. Thorax burdens of thorium using a double filter device. Bull. Radiat. Prot.13, 31–33 (1990).
5. Jacobi, W. A double filter device to measure radon and thoron in breath. In: Assessment of Radioactivity in Man. Vol. II, STI/PUB/84 (Vienna: IAEA) pp. 275–289 (1964).