A 2.0g sample of the fission product cesium-137 is placed in a secure storage cask immediately after it leaves a reactor. The half-life of cesium-137 is 30 y. Its molar mass is 137g mol−1. Regulatory guidelines require that the sample’s activity must fall below 1.0×1012 decays s−1 before it can be transferred to a less shielded facility. The Avogadro constant is 6.02×1023mol−1.
(a) Determine the initial activity of the sample when it is first placed in the cask.
(b) Calculate the time, in years, required for the activity of the sample to decrease to the regulatory threshold.