Assessment of the²²⁰ Rn Franction Retained in Mice after a Single Injection of${}^{224}{\rm Ra}$

The time course of${}^{224}{\rm Ra}$,${}^{212}{\rm Pb}$, and²¹² Bi retention and²²⁰ Rn exhalation was measured in two groups of mice after a single intraperitoneal administration of${}^{224}{\rm Ra}$. The retained²²⁰ Rn fraction was calculated using two approaches: (1) From measured activity of²²⁰ Rn in exhaled air and from${}^{224}{\rm Ra}$ retention data. (2) From the measured${}^{212}{\rm Pb}$ or²¹² Bi retention and using a theoretical time course of the retention of these radionuclides; it was assumed in this case that the retained²²⁰ Rn fraction is constant within the duration of the experiment, i.e., during the first 3 wk after${}^{224}{\rm Ra}$ administration. The retained fractions found using the two approaches are in good agreement equaling 60-70% in both groups of mice; thus the fraction exhaled amounts to 30-40%.