A freshly isolated sample of 90Y was found to have an activity of 9.8 * 10⁵ disintegrations per minute at 1:00 p.m on December 3, 2003. At 2:15 p.m on December 17, 2003, its activity was redetermined and found to be 2.6 * 10⁴ disintegrations per minute. Calculate the half-life of 90Y.
