A Radioactive Source of ¹³⁷Cs (T_1/2= 30 Y) Was Calibrated $\mu$

A radioactive source of ¹³⁷Cs (t_1/2= 30 y) was calibrated on October 23, 2000, to contain 10 $\mu$ Ci.This is used as a daily accuracy check source in the dose calibrator.Presuming the dose calibrator is working properly, what activity should the dose calibrator show on April 23, 2006?

A) 9.6 $\mu$ Ci
B) 8.8 $\mu$ Ci
C) 5.4 $\mu$ Ci
D) 2.2 $\mu$ Ci