Physics 1 Flashcards
What two models replaced the bohr model?
Standard model and quantum mechanical model
What is the standard model of atoms?
Describes subatomic particles (quarks, electrons) and force carrier particles (photon, gluon, bason).
What is the quantum mechanical model?
Describes arrangement of electrons in atom (orbitals).
Atomic number (Z)
Number of protons, identity of element
Atomic mass (A)
Number of protons and neutrons. Determines stability of element.
What is ionization?
A neutral atom loses an electron. Creates a positive aton and negative free electron.
What is electron binding energy?
Energy that atom holds onto electron. Binding energy increases the closer to nucleus. Larger atoms have higher binding energy.
Where are electrons produced in x-ray machine?
The tube.
Where are electrons produced?
The cathode (negative charge)
What is the anode?
Tungsten target surrounded by copper heat sink (positive charge). Where photons are produced.
What is the cathode filament?
Tungsten wire that is heated by low voltage source and emits electrons proportional to the temperature.
What is the focusing cup?
Molybdenum, is negatively charge that surrounds cathode to direct electrons towards anode focal point.
What occurs when you have a smaller tungsten anode target?
Produces sharper image but more heat.
How much of the energy at anode target is converted to x-rays?
1%…..99% is converted to heat. Radiation produced at anode.
What are the characteristics of tungsten target?
High atomic number-efficient x-ray production
High melting point-withstand heat
High thermal conductivity-dissipate heat
Low vapor pressure-maintain vacuum in tube.
What is radiation?
Transmission of energy through space and matter.
What is particulate radiation?
Breaking up atoms into alpha/beta particles and gamma rays.
What is radioactivity?
Emission of ionizing radiation or particles by spontaneous disintegration of nucleus. Part of particulate radiation.
What is electromagnetic radiation?
Movement of energy through space as electric and magnetic fields. Consist of photons (Electron volts). Created when velocity of electrically charged particle is altered.
Bremsstrahlung radiation
Sudden stopping or slowing of electrons to produce photons (x-rays). Direct hit or near miss of nucleus. Produce majority of x-rays!
Characteristic radiation
Moving electron hits and ejects inner electron. Outer orbital electron replaces and releases photon to go to lower energy state.
Voltage
Electromotive force-determined by the potential difference between two points. The greater the potential difference the faster the electron will move.
What type of voltage do you want at the tube?
High voltage. Alternating current creates peak.
Kilovolt peak
the peak voltage created by alternating currents.
What type of voltage across the filament?
Low voltage to prevent burnout of filament. (10V)
What is current?
The measure of flow of the electrical charge. Charge cannot flow without voltage.
Filament current?
Number of electrons through filament
Tube current?
Number of electrons from cathode to anode.
high voltage (step up) transformer
Boost incoming voltage to 60-120kV for tube voltage. Can change peak voltage with dial.
What is the quality of the beam
Energy of the beam that is controlled by kVp (voltage).
Filament (step down) transformer
Reduces voltage and regulated by mA selector. Regulates filament temperature and number of electrons emitted by cathode.
What is the quantity of the beam
Number of electrons and controlled by amps (mA).
Factors that control x-ray beam?
Exposure time, tube current, tube voltage peak, filtration, collimation, inverse square law.
What is exposure time?
Measured in seconds. Number of photons proportional to the number of seconds.
Tube current effect on x-ray beam
Number of photons/x-rays are proportional to tube current. Number of x-rays is multiply exposure time with amps.
Tube voltage peak (kVp)
Increase voltage increases potential difference between anode/cathode. Increases number of photons, mean energy of photons, maximal energy of photons.
X-ray filtration
Only photons with sufficient energy are filtered out
Inherent filtration
Materials photons encounter as travel from focal spot to detector (glass, oil)
Added filtration
Aluminum disk that are added.
Total filtration
Inherent plus added filtration
Collimation
Used to restrict beam size by using lead. Limits x-ray to patient and reduces compton scatter. Rectangular collimator preferred
Inverse square law
Intensity of beam inversely proportional to inverse square distance (I1)/(I2)/(D2)2/(D1)2
What are attenuation interactions
Loss of x-ray beam intensity. Absorption interactions and scattering interactions.
Absorption interactions
photon absorbed and electron ejected. Photon cease to exist.
Scattering interactions
Photons interact with atom then move off in another direction.
Photoelectric absorption
Inner shell electron absorb photon, is ejected then outer shell electron takes its place and releases photon that has low energy. Photon absorption occurs with higher density of the third power of atomic number. Primary contributor to image.
Coherent scattering
Low energy photon excites atom, excited atom sends off different photon at same energy in different direction that isn’t detected in film
Compton scattering.
Photon interacts with electron, electron ejected and photon is deflected.
What are the primary beam loss (attenuation)
Photoelectric absorption and compton scatter.
What is the half value layer
Penetrating power determined by energy of beam (kVp) and density of material. Half value layer is the thickness of material that reduces intensity of x-ray beam in half.
