This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Radiology
[{'content': "The' 1/2 life of CO60 is: \nSelect and explain. \nA. 2.6 years, B. 5.2 years, C. 8 years, D. 3200 years", 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ans. 5.2 years', 'role': 'assistant'}]