UPTAKE OF 226RA FROM IRRIGATION WATER BY BASIL CROPS.

The transfer of 226Ra from irrigation water to basil crops was studied in field conditions. A dedicated basil plot was established and divided into test and control subplots irrigated with water having high (2.1 Bq L-1) and low (0.05 Bq L-1) activity concentrations of 226Ra, respectively. The experiment was performed over a period of 18 months during the autumn, winter and spring seasons, altogether eight cycles of growth and harvest. The activity concentration of 226Ra in basil grown in the test subplots was found to increase from a value of 0.6 Bq kg-1 up to 5.1 Bq kg-1 with successive cycles, compared to a mean value of 0.2 Bq kg-1 for basil grown in the control subplots. The increase in activity concentration of 226Ra in basil grown in the test subplots is mainly attributed to its build-up in the soil in which the level of 226Ra was found to increase by ~ 40%. The effective uptake of 226Ra from the irrigation water (via soil) by the basil plants was found to be approximately 0.4%. The maximal radiation dose following consumption of basil crops grown in the test subplots is negligible (~3 µSv/y).

Detailed effects of particle size and surface area on 222Rn emanation of a phosphate rock.

The dependency of radon emanation on soil texture was investigated using the closed chamber method. Ground phosphate rock with a large specific surface area was analyzed, and the presence of inner pores, as well as a high degree of roughness and heterogeneity in the phosphate particles, was found. The average radon emanation of the dry phosphate was 0.145 ± 0.016. The emanation coefficient was highest (0.169 ± 0.019) for the smallest particles (<25 µm), decreasing to a constant value (0.091 ± 0.014) for the larger particles (>210 µm). The reduction rate followed an inverse power law. As expected, a linear dependence between the emanation coefficient and the specific surface area was found, being lower than predicted for the large specific surface area. This was most likely due to an increase in the embedding effect of radon atoms in adjacent grains separated by micropores. Results indicate that knowledge of grain radium distribution is crucial to making accurate emanation predictions.