The diffusion of 99 Tc in granite was investigated with small-sized diffusion cells, composed of a radioactive source solution cell and a sampling cell. Water in the two cells was kept at the same level. 1 ml aliquots were taken from the sampling cells daily during the first 50 days, then at intervals of several days, and measured via liquid scintillation counting. The experimental results indicate that the diffusion of 99 Tc and 3 H in granite follows the one-dimensional diffusion equation when diffusion time is long enough (> 100 days). The calculated average diffusion coefficient of 99 Tc (1.4 × 10 −12 m 2 /s) is about one half of that of 3 H (3.2 × 10 −12 m 2 /s).

Migration / 99 Tc / Unsaturated Chinese loess / Artificial rainfall / In situ testSummary. The migration of 99 Tc in unsaturated Chinese loess under artificial rainfall condition was investigated in situ. Water suckers were buried at different depths under the bottom of an experimental pit of 2 m × 2 m × 1 m (deep). Quartz containing 3 H and 99 Tc was introduced into the experimental pit to an area of 40 cm × 40 cm and the pit was backfilled to a thickness of 30 cm. An artificial rainfall of 5 mm/h was applied to the experimental pit 4 h a day for 3 months. Moisture water samples were sucked with the help of a vacuum pumping system and the activity of 3 H and 99 Tc in the samples was determined. Breakthrough curves of 3 H and 99 Tc indicated that 99 Tc was slightly retarded. The calculated average apparent distribution coefficient of 99 Tc in the medium was (1.98 ± 0.42) × 10 −2 ml/g.