A study of grain size effect on radon exhalation rate and uranium content of a phosphate rock

Assessment of the exhalation rate allows a classification of materials according to their potential risk of exposure to radon. The present study investigates the granulation effect on the radon exhalation rates from a phosphate sample. The phosphate sample was sieved into different grain size dimensions ranging from < 0.063 to > 2 mm. The exhalation rate of each fraction was measured using the accumulation method. The radon exhalation rate was found to decrease with an increase in grain size above 0.125 mm. The influence of grain size on uranium content was also studied using the autoradiography method. The uranium concentration increased for the smallest grains (< 0.25 mm), reached a maximum for the grains (0.25–0.5 mm), and decreased for the larger grains (> 0.5 mm). The measured values of radon exhalation rates are under the limits reported worldwide.