Änderung der zeitlich-räumlichen Verteilung von228Ra und224Ra im RES und markfreien Skelet nach Inkorporierung von kolloidalem ThO2 (Thorotrast)
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Variation with time of the distribution of228Ra and224Ra in the RES and marrow-free skeleton after incorporation of colloidal ThO2 (thorotrast)
Animal experiments were done in order toanswer the question for the variation with time of both the distribution of Th-232 and its daughters and the activity ratios between the radionuclides of the thorium decay chain immediately fter incorporation ofthorotrast.
The results of these investigations indicate a continuous elimination of Ra-224 from ThO2-aggregates in the organs of the RES, liver, spleen, and red bonemarrow. According to the variation with time of the activity ratio between Ra-224 and Th-228, even from the first day after incorporation, about 35% of the Ra-224 atoms formed in the aggregates may leave the aggregates due to recoil at α-decay of Th-228 and will be eliminated from the organs of the RES. This means that at least at that time the process of aggregation of the ThO2-particles within the organs of the RES has to be finished.
This portion of Ra-224 being eliminated from the RES is partly translocated into the marrow-free skeleton. The same is true for the portion of Ra-224 and R-228 in ionic form at the total activity of the suspension, that means, according to the range of the Ra-228 and Ra-224 recoil atoms within the ThO2-particles, for 80% to 90% of the total Ra-228 and Ra-224 activity of the suspension.
From the variation with time of the specific Ra-228 activity of marrow-free bone it could be seen that Ra-228 and Ra-224 being fixed in the marrow-free skeleton in ionic form at the time of incorporation is eliminated from the skeleton according to a potential function. As consequence of a continuous translocation of Ra-224 to the skeleton due to decay of Th-228 within the organs of the RES the specific Ra-224 activity of marrow-free bone proved to be constant between 10 nd about 100 days fter incorporation ofthorotrast, considering decay of Ra-224 within the skeleton and its elimination from the skeleton.
The experimental results were correlated to those of a theoretical model describing translocation of Ra-224 from the RES to the marrow-free skeleton and its excretion from the skeleton and the body.
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