Gallium-67 is used medically in tumor-seeking agents. The half-life of gallium-67 is 78.2 hours. If you begin with 39.6 mg of this isotope, what mass remains after 215 hours have passed? mg Submit Answer Retry Entire Group 9 more group attempts remaining Iron-59 is a radioisotope that is used to evaluate bone marrow function. The half-life of iron-59 is 44.5 days. How much time is required for the activity of a sample of iron-59 to fall to 12.9 percent of its original value? days Submit Answer Retry Entire Group 9 more group attempts remaining PIC COLLAGE