91 (10%) Problem 5: A scientist has a 1.6-g sample of pure strontium-91, 31 Sr. The half-life of strontium-91 is 9.70 h. 15. 33% Part (a) Determine its decay constant in units of = 1.985 * 10-5 = 1.985 x 10-5 s-1 Correct! 33% Part (b) Determine the initial number of nuclei strontium-91 nuclei initially in the sample. No = 1.06 * 1022 No = 1.060 1022 nuclei Correct! : 33% Part (c) Determine the activity in units of becquerel after 12 hours. A = | Bq