Adsorption and desorption of radioactive inert gases in various materials

Peculiarities of the 85Kr and 133Xe adsorption and desorption processes in active carbon and paraffin are considered in the work. During the desorption process, the distribution of 85Kr and 133Xe atoms in active carbon particles is uneven: atoms in narrow micropores desorb the last. It is shown that by changing adsorption conditions the presence time of radioactive inert gases in an active carbon can be prolonged. The adsorption and desorption processes change in the adsorbent, which changes its aggregation state: adsorption occurs in a liquid absorbent and desorption - in a solid absorbent. Paraffin is just such an absorbent changing its aggregation state with low energy losses. It has been obtained that 133Xe accumulates less in liquid paraffin that in an active carbon. The absorption of 85Kr in paraffin is larger than in an active carbon (at 18-20 degrees Celsius), while desorption is slower. The velocity of radioactive inert gas atom motion in different places of a solid paraffin sample is different - it increases approaching the borders of the sample. Prolongation of the desorption time of radioactive inert gases from adsorbents and adsorbents in many cases is of a practical importance. In this work, it has been shown by model experiments that the intensity of adsorption and desorption processes for the same sorbents can be changed. Desorption intensity changes are related to the distribution of gas atoms on the surface of particles and in micropores. Desorption velocity decreases if inert gas atoms having entered micropores are 'closed' by condensed liquids in the environment. In this case an inert gas atom diffuses within the whole particle volume or through the condensed liquid. Radioactive inert gases 85Kr and 133Xe are absorbed not only in liquid paraffin but in solid one as well. Therefore, after a paraffin sample is hermetically closed in a glass dish, 85Kr (gas) having diffused from this sample is repeatedly absorbed in it. The 85Kr concentration within the sample is 2-3 times higher than that at its borders. Therefore, in the air between the paraffin sample and the dish walls a high 85Kr partial pressure does not occur and the gas does not get out from the dish. (author)