The results of the deposition of tritium oxide (HTO) from atmosphere to Hypogymnia physodes lichens during chamber experiments are presented. For lichens the content of tissue water tritium (TWT) and organically bound tritium (OBT) were measuremed. Were shown that lichens mainly absorb HTO from atmosphere during first 24 hours. The ratio TWT/HTO of chamber and the velocity of TWT to OBT conversion in lichens were determined. Was noted that the TWT to OBT conversion velocity for lichens is ten times greater than that for deposition of HTO by vascular plant leafs. There was supposed that TWT to OCT conversion in lichens is occurred through alga as well as fungus component of lichens. The intensive deposition HTO from chamber atmosphere by lichens and high velocity of HTO to OBT conversion show the availability to use lichens for determination of atmosphere pollution by HTO.

It is known that lichens are used for assessment of atmosphere pollution by heavy metals, radioniclides, sulfur and nitrogen oxides, etc. However there were published in scientific literature only limited data on usage of lichens as bio-indicators of tritium (1,2). There are presented in the paper the results of lichen application study for assessment of atmospheric pollution by tritium. Both tritium in tissue free water (TFWT) and organically bound tritium (OBT) were measured in lichen. Lichen species Hypogimnia physodes was used as a basic bio-indicator. Pieces of lichen were sampled within the distance of 30 km of emission source. Established sampling sites were rectangular in shape with linear dimensions 100*100 in. Lichen samples were sampled from various trees: birch tree, aspen tree, pine tree and linden tree at the level of 1.5 in above the ground. Thermal vacuum desorption technique was used to extract TFWT from lichen samples. Pyrolitic oxidation of dried lichen samples by vanadium oxide was used to extract tritium from OBT. Air monitoring stations equipped with active and passive samplers were used to sample HT and HTO from the atmosphere. Liquid scintillation counting was used to measure tritium content in water samples.It was determined that tritium content in lichen samples (both in TFWT and OBT) in vicinity of an emission source is higher than that of tritium content in lichen at distant sampling sites. Variation of tritium activity of TFWT was about 10 times, variation of tritium activity in OBT was about 70 times. It was supposed that tritium content in TFWT was in equilibrium with tritium content in atmosphere at the minute of sampling, while tritium content in OBT was determined by tritium content in atmosphere over longer period of time.

There are presented in the research results of HTO washout and the model of HTO atmosphere concentration in the vicinity of a long-term HT and HTO emission source. The site of the scavenging experiments was around a 30 m emission source. The sampling arcs were chosen at 150-300 m from the base of the source to minimize dry deposition on the precipitation collectors. To study dependence of scavenging of tritium on raindrops characteristics, an optical device was constructed and used to measure the distribution of the drop radii and velocities during the period of experiment.The washout model, used for assessments, takes into account dispersion, deposition and re-emission. The model of HTO wet deposition is taken into account kinetics of HTO exchange between vapor and liquid phase with parameters such as rain drop spectra, rain intensity, condensation-evaporation on drop's interface. Gauss type formulae for permanent emission source is used to calculate HTO atmospheric concentration. Meteorological data are used as input parameters for modeling.

This paper presents a method of investigation and equipment for studying kinetics of washout tritium oxide (HTO) from air by water drops in laboratory conditions. Water drops' radii of 0.14, 0.17 and 0.21 cm and different times of contact with HTO (different time of flight through HTO vapour) were studied — the concentration of HTO in the drop's water is proportional to the concentration of HTO vapour, drop size and the drop's duration of flight. Moreover, the average rate of exchange was 0.47 ± 0.02 cm s−1. The rate-limiting stage of the HTO washout mechanism by raindrops is discussed.