Intro to physics part Flashcards
Matter
-anything that has mass and takes up space
-Made of atoms containing protons, neutrons and electrons
Z*
= atomic number = # of protons
-defines the element
-in the top left corner of box
A
= mass number (protons + neutrons)
Atoms of importance:
W, H, C, N, O, Ca
W = Tungsten. Z* is 74 and A (mass number) is 183. This is the metal target that we throw e-‘s at to produce x-rays.
H = Hydrogen. Z* is 1 and A is 1.
C = Carbon. Z* is 6 and A is 12.
N = Nitrogen. Z* is 7 and A is 14.
O = Oxygen. Z* is 8 and A is 16.
Ca = Calcium. Z* is 20 and A is 40.
Electrons
-Orbit in DISCRETE ENERGY SHELLS ( K, L, M, etc)
-Bound by ELECTROSTATIC ATTRACTIVE FORCE with positive protons (that are in the nucleus)
-think of bohrs model
Factoid
Q: if the nucleus were blown up to the size of a marble (1 cm), where would the nearest electron be?
A: One kilometer (0.62 mi) away
Electron binding energy (Eb)
-Minimum energy required to remove an e- from a specific shell
-Nucleus = ~MeV
-Inner shell= !Kev to 10s kev
-outer shell = ~ev
What is electron binding energy dependent on?
-it is directly dependent upon number of positive protons (Atomic number, Z)
-Indirectly dependent on distance AWAY from nucleus (Orbital shell)
Ionization + Ionization Energy
-Process by which atom acquires +/- by gaining or losing electrons
-Requires “sufficient energy to overcome electron binding energy”
-Dependent upon Z and orbital shell
-able to cause biological detriment
Electron Transitions
-Concept: Electrons want to be closer to nucleus
-ionization resulting in ejection of electron leaves vacancy that must be filled
-“Electron Cascade” occurs to fill vacancy. Results in release of energy
Key Concepts
-Atomic number (Z) = number of protons
-Eb = electron binding energy = energy required to release electron from shell
-Increase Z = increase Eb
-Increase distance from nucleus = decrease Eb
-Electron cascade results in release of energy
High Speed electrons traveling toward a metal target will:
(2 ways an x-ray is produced)
1) Slow down after interacting and release a photon whose energy is equal to subsequent kinetic energy difference (this change in kinetic energy is released as an x-ray)
2) Cause release of electrons from the target atom, which then triggers electron cascade with subsequent release of energy
Both instances release x-ray radiation
Radiation
-Definition: Transmission of energy through space and matter
-Nature of radiation takes two forms: 1)Electromagnetic radiation
2) Particulate radiation
Particulate radiation
-Defined mass and kinetic energy, with or without charge
-produced by nuclear decay
-used in advanced imaging such as PET (positive electron transmission), bone scintigraphy
-made up of any subatomic particles such as protons, neutrons and high speed electrons capable of causing ionization
Electromagnetic radiation (EMR)
-Travel as combination of electric + magnetic waves perpendicular to direction of propagation
-photons with NO mass or charge
-Velocity equal to speed of light (~3 x 10^8 m/s)
EMR Characteristics
-Interrelated parameters:
1) Wavelength (m or nm)
2) Frequency = v (Hz or MHz)
3) Energy = E (eV or keV)
Things with higher frequency have more energy
EMR: Wave-particle duality
Energy of photon:
-Inversely dependent on wavelength
-directly dependent on frequency
E is proportional to (1/wavelength) which is proportional to V (frequency)
EMR Spectrum
-EMR grouped according to wavelengths along spectrum
-Energy range for diagnostic x-rays is 40 to 150 keV
-for x-rays: wavelength is 10^-10 m and frequency is 10^ 18 Hz
Ionizing versus non-ionizing radiation
-Ionizing radiation: Higher frequency (>10 keV) = higher energy = capable of removing bound electrons (X-ray imaging)
-non-ionizing radiation = lower frequency = insufficient to remove bound electrons (MR imaging)
Key Concepts
-Radiation = Transmission of energy through space and matter
1) EMR possess no mass or charge, has kinetic energy and is produced by altering velocity of electrically charged particles
-wave-particle duality illustrates x-ray photon E depends: indirectly on wavelength and directly on frequency of EMR
2) Particulate radiation possess mass and kinetic energy, may or may not be charged and is produced by radioactive decay
-Ionizing radiation has sufficient energy to eject electron which has potential for biological detriment
Production of X-rays
-via conversion of electron KE into EMR when incident electrons:
1) Decelerate by interaction with target atom
2) Eject a targets orbital electron thus triggering electron cascade with release of energy
Bremsstrahlung Radiation
-“Braking radiation”: loss of KE in form of x-ray
-primary source of diagnostic x-rays
-** Energy of photon dependent upon site of interaction. The closer the electron hits to the nucleus, the higher the energy of the photon
-Deflected electrons have less energy than the incident electrons
-Direct impact with nucleus = MAXIMUM energy
-Close interaction = Higher energy
-Distant interaction = lower energy
Quantity of Bremsstrahlung
-quantity of bremsstrahlung is proportional to Z^2 of target atom –> Why?
-High Z = higher # protons = greater electrostatic force = greater deflection = #bremsstrahlung emitted
Quality of bremsstrahlung
-quality of bremsstrahlung is proportional to speed/ acceleration of incident electron (kVp)
-Fast electron = more KE to convert = higher E photon
-Slow electron = less KE to convert = lower E photon
-Higher frequency = high E photon
-Low frequency = low E photon
Bremsstrahlung radiation is heterogenous energy
-continuous spectrum of energy (Heterogenous energy)
-Why a continuous spectrum? –> 1) Incident electrons pass at various distances = varied deflection and release of energy
2) Each incident electron may have multiple bremsstrahlung interactions = reduced energy
3) Varying voltage between target and filament = varied KE of incident electrons
Characteristic Radiation
-Result of electron transitions between atomic shells during electron cascade
-Radiation may be in visible, UV, + x-ray portions of EM spectrum depending on energy of photon
-Energy of photon is always going to be SLIGHTLY less than vacancy shell electron binding energy
-Discrete x-ray energy peaks specific to level of vacant orbital
-energy of characteristic x-ray is proportional to atomic number
