This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Physics of Radiotherapy, Subject name: Radiology
Iridium 192 half life 
Select and explain. 
A. 2.7 days, B. 8 days, C. 74 days, D. 16 hours
C: 74 days
Answer: C: 74 days 
Explanation: Ans. (c) 74 daysRef: Basic radiological physics 2nd ed. /180* Iridium-192, emits gamma rays. It has energy of 0.4MeV.* Tl/2 of iridium 192: 74 daysImportant Half Life of Radionuclides* Gold-198: 2.7 days* Iodine- 123: 13.3 hours* Iodine-131: 8 days* Phosphorus-32: 14.3 days* Yttrium 90: 64 hours* Cobalt-60: 5.26 years* Caesium-137: 30 years* Radium-226: 1620 years