Principles of X-Rays and the rotating-anode X-ray tube 0.0 / 5 ? PhysicsMedical physicsA2/A-levelAQA Created by: LZ95Created on: 15-06-14 19:22 What are X rays? Very high frequency electromagnetic waves produced when high-energy electrons lose energy as they collide with atoms. 1 of 17 Why are the two electrodes in an evacuated glass tube? So that there is no collision between electrons and air molecules, allowing the electrons to travel at high speeds 2 of 17 Where are the electrons accelerated from and where are they accelerated to? Cathode to Anode 3 of 17 What happened when a fluorescent screen was placed a few metres from the tube? It produced light when the tube was operating 4 of 17 Why does the anode rotate in the rotating-anode X-ray tube? So that electrons strike different areas of the target so local heating problems are reduced. 5 of 17 How are electrons emitted from the Cathode? Cathode is heated by a current and electrons emitted due to thermionic emission 6 of 17 What happens when electrons reach the tungsten target? They collide with target atoms 7 of 17 What is 'bremsstrahlung'? A continuous spectrum of X ray as a result of the slowing down of electrons 8 of 17 What happens when high speed electrons have sufficient energy and collide with the electrons of target atoms? Electrons of target atoms knocked out of their orbits and atoms are ionised 9 of 17 Why are characteristic X rays emitted? Other electrons in target atoms move down energy levels to fill the gap 10 of 17 What does the max. potential energy of an X ray photon depend on? P.d. 11 of 17 What energy does an electrons gain when it is accelerated? E= eV 12 of 17 How much of the energy of an electron beam is converted to X-ray radiation and what is the rest transferred as? 1% and rest transferred as internal energy in the target 13 of 17 Name 4 features which make tungsten a good target material High thermal conductivity, high specific heat capacity, high melting point, high atomic number 14 of 17 Why is it good in X ray production if the target material has a high atomic number? Material has larger mass so this increases the probability that collisions result in X ray emission 15 of 17 Why does the anode have a bevelled edge? So that target can be wide without increasing the width of the X ray beam 16 of 17 How can you change the intensity of X rays? By changing the current supplied to the cathode 17 of 17
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