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
Alpha paicle has: September 2011 
Select and explain. 
A. 1 proton, 2 neutrons, B. 1 proton, 1 neutron, C. 2 protons, 1 neutron, D. 2 protons, 2 neutrons
D: 2 protons, 2 neutrons
Answer: D: 2 protons, 2 neutrons 
Explanation: Ans. D: 2 protons, 2 neutrons Alpha paicles are simple helium nuclei (i.e. consisting of 2 protons and 2 neutrons) Remember: Alpha rays: Most ionizing Gamma rays: Maximum penetration power Cesium-137, cobalt and radium emits predominantly: Gamma rays