The activity of a sample is 64×10-5 Ci. Its half-life is 3 days. The activity will become 5×10-6 Ci after 
(a) 12 days          (b) 7 days
(c) 18 days          (d) 21 days

(d) A=A012t/T1/25×10-6=64×10-512t/31128=12t/3t=21 days

Difficulty Level:

  • 22%
  • 16%
  • 22%
  • 43%