This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Fundamentals in Radiology, Subject name: Radiology
[{'content': 'Which of the following has maximum ionisation potential? \nSelect and explain. \nA. Electron, B. Helium ion, C. Proton, D. Gamma photon', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Helium ion (alpha rays) has maximum ionisation potential Gamma rays have maximum penetration power.', 'role': 'assistant'}]