IEM SF1

• Electrification


  Whenever electrons are added to or removed from material, the material is said to be electrified
• Ways of electrification


  • Contact
  • Friction
  • Induction
• Electrification by Contact


  Occurs when an object having an excess number of electrons contacts a neutrally charged object or an object with a deficiency of electrons
• Electrification by Friction


  Occurs when we rub two neutral bodies, there will be some transfer of electrons from one body to the other due to structural modifications because of the frictional forces acting on them
• Electrification by Induction


  Occurs when a highly electrified object comes close to a neutral object so that the electrons are transferred by spark
• Potential Difference


  Is the difference in electric potential between two points in an electric field. It represents the work done per unit charge in moving a positive test charge between the two points, measured in volts (V). In radiology, potential difference refers to the voltage applied across the X-ray tube to accelerate electrons, which is crucial for generating X-rays used in imaging.
• The most familiar form of electrical energy is normal household electricity, which involves the movement of electrons through a copper wire by an electric potential difference of 110 volts (V)
• All electric apparatus, such as motors, heaters, and blowers, function through the use of electrical energy
• A potential difference of about 25,000 V is maintained across the tube between photocathode and anode so that electrons produced by photoemission will be accelerated to the anode
• Electron volt (eV)


  Unit of energy equal to that which an electron acquires from a potential difference of 1 V
• Electric Current/Electricity


  The flow of electrons through a conductor
• Direction of electric current

  Always opposite the electron flow
• Electric current unit


  Amperes (A)
• 1 A


  1 C/s or 1 electric charge/second
• Increasing electric resistance


  Results in a reduced electric current
• Tube Current / X-ray Tube Current


  The flow of electrons from cathode to anode, measured in milliamperes (mA)
• Direct Current


  Electrons that flow in only one direction within a conductor
• Indirect Current


  Electrons that flow alternately in opposite direction, 60-Hz current, Oscillation of electricity in both directions within a conductor
• Alternating Current (AC)


  Current in which electrons oscillate back and forth, waveform is a sine curve
• Rectification


  The process of converting alternating current (AC) to direct current (DC)
• Rectifier


  The device that can convert an alternating current (AC) to direct current (DC)
• Resistance


  A measure of the opposition to current flow in an electrical circuit, measured in ohms (Ω)

  
• Types of materials based on resistance

  • Conductors
  • Insulators
• Conductors


  Materials that offer very little resistance where electrons can move easily, most metals are good electric conductors, copper is one of the best, water is also a good electric conductor because of the salts and other impurities it contains
• Insulators


  Materials that present high resistance and restrict the flow of electrons, glass, clay, and other earth like materials are usually good electric insulators
• In 1946, William Shockley demonstrated semiconductor
• The principal semiconductor materials are silicon (Si) and germanium (Ge), this development led to microchips and hence the explosive rise of computer technology
• At room temperature, all materials resist the flow of electricity

  Resistance decreases as the temperature of material is reduced
• Superconductivity


  The property of some materials to exhibit no resistance below a critical temperature (Tc)
• Magnetism


  The fundamental property of some forms of matter, it has no smallest unit, the polarization of a material
• Magnetism has become increasingly important in diagnostic imaging with the application of magnetic resonance imaging (MRI) as a medical diagnostic tool
• Magnetism is perhaps more difficult to understand than other characteristic properties of matter, such as mass, energy, and electric charge, because magnetism is difficult to detect and measure. We can feel mass, visualize energy, and be shocked by electricity, but we cannot sense magnetism
• Electric Ground


  The object that behaves as a reservoir for stray electric charges
• Proper grounding is essential in low noise electronic design, including circuits for energy dispersive x-ray detectors such as PINs and SDDs. Improper grounding in a system with multiple devices will lead to cross-talk between devices, negatively affecting low-noise performance, and in the case of energy dispersive x-ray detectors, degrading energy resolution and adding low energy noise. The electronic signals from Si-PIN and SDD x-ray detectors are very small and very sensitive to noise coming from other devices
• Ground loops usually cause energy dispersive detectors to have increased low energy counts and impaired energy resolution. Failing to follow proper grounding procedures will likely reduce the capability of the system
• Circuit Breaker


  An electromechanical device used to supply power to the control panel and prevents equipment overload, acts in the same manner as a fuse, if the current flow rises excessively, the circuit breaker's internal switch is tripped (opened), stopping the flow of electricity
• Resistor


  A device designed to inhibit the flow of electrons, thereby precisely regulating the flow of electricity through that part of the circuit where it is placed
• Rheostat


  An adjustable or variable form of resistor
• Switch


  A device that opens a circuit (breaks the pathway)
• Transformer


  A device that can increase or decrease voltage by a predetermined amount