Monitoring for Th-228

The upper figure to the left below shows the lower limit of detection (LLD) of monitoring for inhalation of Th-228 (type S, 5 µm AMAD) based on direct measurement of Th-228 in urine and indirect measurement of Pb-212 in the lungs, respectively. As can be seen, the measurement of Pb-212 in the lungs is much more sensitive with respect to the dose from Th-228 than the direct measurement of Th-228 in urine. In the range from 10 d to 100 d after intake the LLD of the measurement of Pb-212 in the lungs is close to the required value for routine monitoring (1 mSv), and thus this kind of measurement could be a useful tool for monitoring of type S material.

In the case of type M material the situation is vice versa, i. e. the measurement of Th-228 in urine is more sensitive than the measurement of Pb-212 in the lungs, but even here the LLD of the measurement of Pb-212 in the lungs is close to the required level in the mid time range.