Radiologic Science Chapter 5 X-ray Tubes Questions and Answers, A+

Cathode contains (negative electron) - filament which is heated to boil off the projectile electrons Cathode shape - like a cup to focus the projectile electrons onto the positive anode anodes (positive electrons) - rotates in order to spread heat from the projectile electrons over a larger area of the anode focal spot - anode Primary Beam - The x-rays that are emitted through the thin window of the tube housing Tube Housing - lead equivalent that limits leakage radiation to less than 100 mr/ hr at 1 meter x-ray Tube - Vacuum tube containing an anode and a cathode that produces a x-Ray beam Pyrex glass - special type of glass that can withstand very high temperatures from the x-ray tube anode Tungsten - the filament in an x-ray tube made of Thermionic Cloud - The function of the cathode is to produce? Filament - provides projectile electrons for Thermionic emissions - The Process In Which Current Passes Through The Cathode Filament & Heats It To An Extremely High Temperature. "boiling off" of electrons occurs Focal spot size - controlled by filament size usually Large or small small focus improves spatial resolution and sharper image (small .1 to .5mm) Focusing Cup - composed of nickel What is used to focus the electron stream towards the target of the anode? space charge effect - As more and more electrons build up in the area of the filament, their negative charges oppose the emission of additional electrons. This phenomenon is known as: Anode functions - 1. it serves as a target surface for high voltage electrons from the filament and is the source of x-ray photons 2. It conducts the high voltage from the cathode back into the x-ray circuitry 3. it serves as the primary thermal conductor When the projectile electron hit the anode - 99% deposited in anode as heat 1% as electon energy is converted to x-ray photons tungsten-rhenium alloys melting point - 3,400 degrees C Tungsten - 1. high atomic number 2. high melting point 3. heat conduction ability molybdenum (high melting point) or graphite (doubles heating load capacity) - layered under the tungsten target Rotating anode consist of - target, shaft and rotor. rotating anodes spread heat rotor - Inside glass envelope, shaft made from copper and soft iron, only part that rotates during x-ray production process. Actual focal spot - The physical area of a rotating anode focal track, affected by the cathode electron beam, is the