This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Radiotherapy, Subject name: Radiology
Direct action of radiation is the dominant process for 
Select and explain. 
A. X-rays, B. Neutrons and alpha paicles, C. Electrons, D. Gamma rays
B: Neutrons and alpha paicles
Answer: B: Neutrons and alpha paicles 
Explanation: Ionizing radiation acts by two methods: Direct and IndirectDirect action is radiation directly causing DNA damage; example: neutrons and alpha paiclesIndirect action is radiation causing free radical production which acts on DNA; example: photons and gamma raysReference: Khan Physics of Radiation therapy; 5th edition