Matter & Energy Quiz

Matter & Energy

• Matter is anything that occupies space and has mass.
• Mass is the distinguishing characteristic of matter and is measured in kilograms.
• Atoms are the building blocks of matter.
• Energy is the ability to do work.
• Electrical energy is produced when an electron moves through an electrical potential difference.
• Thermal energy is the energy of motion at the atomic and molecular level.
• Nuclear energy is energy contained in the nucleus of an atom.
• Electromagnetic energy (EMR) is radiation and is a transfer of energy.
• Ultrasound is a form of radiation but not ionizing radiation.

Laws of Conservation

• Law of Conservation of Matter: Matter can neither be created nor destroyed.
• Law of Conservation of Energy: Energy may be transformed from one form to another, but cannot be created or destroyed.
• Coulomb's Law: The electrostatic force is directly proportional to the product of the electrostatic charges and inversely proportional to the square of the distance between them.
• Law of Distribution: Electric charge distribution of charges is uniform throughout or on the surface.

Electrodynamics

• The study of electric charge in motion.

Conductors

• Substances through which electrons flow easily.
• Require voltage to move the electron.
• Characteristics:
  • Variable resistance
  • Obeys Ohm's Law
• Examples: Copper, Aluminum, & Water

Insulator

• Substances that do not allow electrons to flow.
• Characteristics:
  • Extremely high resistance
  • Necessary with high voltage for insulation (to protect from electrocution)
• Examples: Glass, Rubber, & Clay

Semiconductors

• Materials that sometimes behave as insulators and sometimes as conductors.
• Characteristics:
  • Can be resistive
  • Can be conductive
  • Basis of computers
• Examples: Silicon, & Germanium

Superconductor

• Materials that allow electrons to flow without resistance.
• Characteristics:
  • No resistance
  • No electrical potential required (voltage)
  • Must be very cold/extreme low temperature
• Examples: Niobium and titanium

Superconductivity

• The property of some matter to exhibit no resistance below a critical temperature.

Electric Circuits

• The path of electron flow from the generating source through the various components and back again.

Electric Current/Electricity

• Flow of electrons through a conductor.
• Direction: Always opposite the electron flow.
• Measured in Amperes (A)

Electric Resistance

• Measured in ohms.
• Increasing electric resistance results in a reduced electric current.

Ohm's Law

• The voltage across the total circuit or any portion of the circuit is equal to the current times the resistance.
• Formula: V = I x R

Alternating Current (AC)

• Electrons flow alternately in opposite directions.
• Electrons flow first in a positive direction and then in a negative direction.
• Sinusoidal wave.

Magnetism

• Oxide of iron (Fe3O4)
• A rodlike stone moving back and forth also called as lodestone or leading stone.

Magnetic Field

• Any charged particle in motion creates a magnetic field.
• Magnetism controls the kVp and operates as an induction device.

High Voltage Generator

• Housed in an equipment cabinet positioned against a wall, close to the x-ray tube.
• Newer generator designs take up less space.
• Reduces patient radiation dose.

Operating Console

• Most familiar to the radiologic technologist.
• Used to control the x-ray tube current and voltage applied to the xray tube.
• Provides control of:
  • Line compensation
  • kVp
  • mA
  • Exposure time
• Most xray systems are designed to operate on 220v power.

Radiation Quantity (mAs)

• Number of x-rays.
• Intensity of the x-ray beam.
• Controlling factor of current.
• High number of electrons, higher heat provided to the x-ray tube.
• Units: mR, mGy or mR/mGya, mAs.

Autotransformer Law

• States that the voltage received and provided by the transformer is directly proportional to the number of turns.
• Vs/Vp = Ns/Np

kVp Meter

• Placed across the output terminals of the autotransformer.
• Actually reads voltage, not kVp.
• Pre-reading kVp meter: Allows the voltage to be monitored before an exposure.

Filament Temperature

• Controlled by the filament current, determines the number of electrons emitted by the filament.

Filament Current

• Measured in Ampheres (A).
• X-ray tube is controlled through a separate circuit called Filament Circuit.
• Operates at currents of 3 to 6 Ampere.

Space Charge Effect

• Phenomena via electrostatic repulsion.
• Electron cloud near the filament.

Thermionic Emission

• Release of electrons from a heated filament.

Precision Resistors

• Used to reduce the voltage to a value that corresponds to the selected milliamperage.

Falling load generator

• Exposure begins at maximum mA, then drops as the anode heats, which results in minimum exposure time.

mA x Exposure Time (mAs)

• Product of x-ray tube current (mA) and exposure time is mAs.
• Measure of Electrostatic Charge (C).

mA meter

• Monitors the x-ray tube current.
• Connected at the center of the secondary winding of the high-voltage setup transformer.
• Ensures electrical safety.

Filament Transformer

• "Filament heating isolation step-down transformer".
• Receives the voltage from the mA selector switch.
• Steps down the voltage to approx.. 12 v.
• Provides current to heat the filament.
• Primary winding: Thin copper, 0.5 to 1Ampere, 150v approximately.
• Secondary winding: Thick, 5 to 8Ampere, 120 V.

Exposure Timers

• Devices that control the duration of x-ray exposure.

Guard Timer

• Terminate exposure after a prescribed time (6s).

Synchronous Timer

• Motor driven.
• Precision device designed to drive a shaft at precisely 60 rev per second.
• Cannot be used for serial exposures.

Electronic Timer

• Most sophisticated, complicated, and accurate of the x-ray exposure timers.
• Allows a wide range of time intervals to be selected and are accurate to intervals as small as 1ms.
• Used for rapid serial exposures, suitable for interventional radiology.
• Most exposure timers are Electronic.

mAs Timer

• Monitors the product of mA and exposure time (Electrostatic Charge – C).
• Terminates exposure when the desired mAs value is reached.
• Provides the highest safe tube current for the shortest exposure for any mAs selected.

Automatic Exposure Control (AEC)

• Device that measures the quantity of radiation that reaches the IR.
• Automatically terminates the exposure when the IR has received the required radiation intensity.

Solid-State Detectors (SSD)

• Used to check timer accuracy (as short as 1 ms)

High Voltage Generator

• Increases the output voltage from the autotransformer to the kVp necessary for x-ray production.
• Heat generated is conducted by the oil, which is used primarily for electrical insulation (DIALA V OIL).
• Three primary parts:
  • High voltage transformer
  • Filament transformer
  • Rectifiers

High Voltage Transformer

• Step Up Transformer.
• Secondary Voltage (kVp) > Primary Voltage (V)
• Secondary Current (mA) < Primary Current (A)
• Secondary Windings > Primary Windings
• Voltage waveform: Sinusoidal.

Turns Ratio

• Ratio of the number of secondary windings to the number of primary windings.
• Example: 500:1 and 1000:1.
• Directly proportional to the voltage.
• Inversely proportional to the current.

Rectification

• Process of converting AC to DC.
• X-rays are only produced by the acceleration of electrons from cathode to the anode and cannot be produced by electrons flowing in the reverse direction (Direct Current).

Voltage Rectification

• Ensures that electrons flow from cathode to anode only.

Rectifier

• Electronic device that allows current to flow in only one direction.

Diode

• Electronic device that contains two electrodes.
• All diode rectifiers were vacuum tubes called Valve tubes (Replaced by Solid-State Rectifiers made up of Silicon).

Semiconductor

• Between Insulator and conductor in the ability to conduct electricity.

P-type Semiconductor

• Have loosely bound electrons (free to move).
• Have spaces called holes (no electrons).
• Holes: As mobile as electrons.

Solid-State P-N Junction

• N-type material placed in contact with p-type crystal.
• It conducts electricity in only one direction.
• Solid-State Diode: A rectifier.

Half-Wave Rectification

• Contains 0, 1, or 2 diodes.
• Voltage is now allowed to swing negatively during the negative half of its cycle.
• Producing 60 x-ray pulses/per second.
• Wastes half the supply of power and requires twice the exposure time.

Full-Wave Rectification

• Contains at least 4 diodes.
• Negative half-cycle corresponding to the inverse voltage is reversed.
• 120 x-ray pulses/second.
• Exposure time is cut in half.
• Used in almost all stationary x-ray.

Single-Phase Power

• Results in a pulsating x-ray beam.
• X-rays produced have a value near zero.
• Single Phase Halfwave voltage ripple: 100%
• Single Phase Fullwave voltage ripple: 100%
• Voltage varies from zero to maximum.

Three-Phase Power

• Voltage impressed across the x-ray tube is nearly constant.
• 6 pulses per 1/60 second.
• Voltage never drops to zero during exposure.
• Has a disadvantage in terms of its size and cost.
• Requires 10-kVp reduction.
• 6-Pulse voltage ripple: 14%

The X-ray Tube

• Special type of diode - contains an anode and cathode.
• Converts electrical energy to electromagnetic energy (x-rays).
• Formula for single-phase power: (0.7)(mA x kVp)/1000

Hematopoiesis Cell Survival

• Exposure to radiation causes a decrease in the number of all types of blood cells in the circulating peripheral blood.
• Lymphocytes are the first blood cells to be affected, depleting within minutes to hours after exposure.
• Recovery of lymphocyte levels is very slow.
• Granulocytes and thrombocytes are depleted 30 days after irradiation and take 2 months to recover.
• Erythrocytes are less sensitive to radiation than other blood cells and take 6 months to 1 year to fully recover.

Radiation Dose Limits

• Students (over 18 years old) have a dose limit of 50 mSv.
• General public has a dose limit of 1 mSv for frequent exposure and 5 mSv for infrequent exposure.
• Embryos and fetuses have a total equivalent dose limit of 5 mSv for gestation, or 0.5 mSv per month.

Cardinal Principles of Radiation Safety (STD)

• Shielding: Positioning shielding between the radiation source and exposed personnel significantly reduces radiation exposure.
• Time: Reducing the duration of exposure to radiation reduces the total radiation dose received.
• Distance: Increasing the distance between the radiation source and exposed personnel reduces the intensity of radiation.

Cytogenetics

• The study of the genetics of cells (cell chromosomes).
• Radiation-induced chromosome aberrations follow a non-threshold dose-response relationship, meaning that any dose of radiation can cause damage.

Radiation Shielding

• One TVL (tenth-value layer) is the thickness of absorber that reduces radiation intensity by 90%.
• A protective apron containing 0.5 mm of lead is equivalent to 2 HVLs (half-value layers), reducing occupational exposure by 25%.
• 1 TVL is equivalent to 3.3 HVLs.