Janice needs to have a gastro-intestinal study. So she is given 375 mg of radiocontrast dye containg Barium-142. The half-life of Ba-142 is 10.6 minutes and its decay is followed by x-ray. After one half-life, of Ba-142 remains. After 31.8 minutes, of Ba-142 remains. After half-lives, 11.7 mg of Ba-142 remains. After minutes, 0.366 mg of Ba-142 remains. Finally, after approximately 3.5 hours - half-lives, only 0.000358 mg remains. The dye is no longer visible to the x-ray and Janice's study is over.