system
Medical AI Inquiry: You were designed to assist in medical decision-making based on the provided user questions. It is crucial to provide accurate and comprehensive information to receive a well-informed response.
user
Half life of cobalt-60: September 2011
assistant
The correct answer is  Ans. C: 5.3 years Half life of cobalt-60 is 5.3 years, therefore in practice have to replaced every 3-4 years Half-lives of impoant isotopes: 1-131: 8 days Rn 222: 3-6 days Co 60: 5.2 years