A freshly isolated sample of 90y was found to have an activity of 5.0 × 105 disintegrations per minute at 1:00 p.m. on december 3, 2006. at 2:15 p.m. on december 17, 2006, its activity was measured a

A freshly isolated sample of 90y was found to have an activity of 5.0 × 105 disintegrations per minute at 1:00 p.m. on december 3, 2006. at 2:15 p.m. on december 17, 2006, its activity was measured again and found to be 1.3 × 104 disintegrations per minute. calculate the half-life of 90y.