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
[{'content': 'What percent of electron energy is converted into heat during production of X-rays? \nSelect and explain. \nA. 99%, B. 94%, C. 89%, D. 84%', 'role': 'user'}, {'content': "Answer: A \nExplanation: The purpose of the target in an x-ray tube is to convert the kinetic energy of the colliding electrons into x-ray photons. The conversion of the kinetic energy of the electrons into x-ray photons is an inefficient process, with more than 99% of the electron kinetic energy converted to heat.\nThe target is made of tungsten, an element that has several characteristics of an ideal target material, including the following:\n\nHigh atomic number (74), allows for efficient x-ray production.\nHigh melting point (3422°C), to withstand heat produced during x-ray production.\nHigh thermal conductivity(173 Wm-1K-1), to dissipate the heat produced away from the target.\nLow vapor pressure at the working temperatures of an x-ray tube, to help maintain vacuum in the tube at high operating temperatures.\n\nKey Concept:\nThe conversion of the kinetic energy of the electrons into x-ray photons is an inefficient process, with more than 99% of the electron kinetic energy converted to heat.\nWhite and Pharoah's Oral Radiology 8th\xa0EDITION", 'role': 'assistant'}]