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177 Cards in this Set
- Front
- Back
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Energy imparted to matter by ionizing radiation per unit mass of irradiated materialUnits? |
Absorbed DoseGray or Rad
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Process whereby energy is taken out of a beam by a meterial and kept within that material
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Absorption
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Charged particle identical to a helium nucleus and made of of two protons and two neutrons
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Alpha particle
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Smallest quantity of an element
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Atom
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Number of protons plus neutrons in a nucleus
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Atomic Mass Number
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Number of protons in a nucleus
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Atomic Number
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Removal of photons from a beam by scatter or absorption
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Attenuation
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A model of radiation interaction that assumes the ionization chamber acts like a tiny cavity inside a uniform phantom
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Bragg Gray Cavity Theory
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Interaction in which high speed lectrons interact with the electrostatic field of the nucleus producing xrays
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Bremsstrahlung
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Covering device for thimble chambers to provide electron equilibrium for high energy photons
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Build up cap
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Xray photons radiated by excited atoms when their electrons drop to lower energy states, always discrete energies
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Characteristic radiation
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Interaction of very low energy xray photon where the incoming photon is redirected at a different angle but at the same energy
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Coherent scatter
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Xray interaction mechanism that predominates at most clinical energies, resulting in both photon and electron scatter
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Compton effect
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Time during which a detector cannot dtect radiation after having detected a radiation particle or ray
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Dead time
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Ratio of dose at depth to dose at D Max depth, expressed as a decimal or percent
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Depth dose
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Dose modified by quality or weighting factor
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Dose equivalent
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Number of electrons per unit cubic distance or mass in a matrial
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Elecrton density
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Ratio of first HVL to second HVL
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Homogeneity Coefficient
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Kinetic energy released in matter
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KERMA
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Ionization chamber located in megavoltage machines that is used to measure and verify precise amounts of radiation to the patient
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Monitor chamber
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Negative electron
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Negatron
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heavy neutral particle that resides in the nucleus of atoms
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Negative ion
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Perpendicular beams
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orthogonalVo
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Voltage between two electrodes in an ionization detector
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Polarization voltage
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Positively charged electron
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Positron
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Xray interaction where the photon energy is given entireley to an electron in an atom
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Photoelectric effect
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Gas used in Geiger tubes to suppress the UV light created by the secondary electrons produced in the initial ionization event
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Quenching agent
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Target used in xray machines
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Reflective target
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Process whereby electrons and positive ions recombine before they can be collected in an ionization chamber
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ion recombination
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Thin metal sheets that provide electrons with which the electron beam can scatter, expanding the useful size of the therapy beam
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Scattering foils
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Solid state radiation detector that absorbs radiation energy and when heated appropriately emits an amount of light related to the energy absorbed
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Thermoluminescent dosimeter
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Areas within patient composed of non water equivalent tissues
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Tissue inhomogeneities
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Type of target used in megavoltage xray machines in which the photon beam is in the same direction as the electron beam
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Transmission target
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Electron in the outermost shell of an atom in its ground state
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Valence
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Enclosed metal device in which microwaves travel
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Waveguide
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Gives high power voltage to power the klystron, magnetron, and electron gun
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Primary Distribution System
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Contains emergency off button, shutting off power to treatment unit
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Secondary Distribution System
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Controls the temperature of the power system
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Fan control
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Amplifies high frequency waves created by a radiofrequency driver
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Klystron
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Creates high-frequency power, supplies energy to accelerator guide
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Magnetron
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Directs RF energy into waveguide and prevents backflow
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Circulator
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Guides electromagnetic waves to the accelerator structure
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Waveguide
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Keeps equipment at a constant temperature
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Cooling system
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Produces electrons sending them to the accelerator structure
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Electron
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Speed up electrons as they approach the treatment head
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Accelerator structure
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Waves go back and forth in the accelerator structure creating a stationary wave
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Standing wave accelerator
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Electromagnetic wave travels to right along with electrons, continuously accelerating. Electron and electric field must move at same velocity
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Traveling wave accelerator
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Allows electron beam to switch from horizontal to vertical towards the patient and the target
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Bending magnet
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Proton beam path
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Electron beam - Target - Collimator - Flattening filter - Ion chamber - secondary collimator - MLC - Accessory mount
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Electron beam path
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Electron beam - collimator - scattering foil - ion chamber -secondary collimator - MLC - accessory mount
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Photon interactionPhoton energies below 10 kev
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Coherent scattering
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Photon interaction-Incoming photon is absorbed by atom's electrons- Atom re-emits a second photon with the same energy as the incident photon but scattered in new direction
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Coherent scattering
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Photon interactionAs photon energy increases the chance of this interaction decreases threefold
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Photoelectric
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Photon interactionThe higher the Z# the chances of this interaction increases threefold
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Photoelectric
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Photon interaction-Incoming photon interacts with an electron in the inner shells of the atom-ALL energy is transferred to electron which then gets ejected from the atom- Empty space filled by outer shell electrons, losing energy in the process creating a photon
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Photoelectric
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If characteristic xray photon is absorbed by an orbital electron instead of leaving the atom, the electron will have excess energy and be ejected from the atom
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Auger electron
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Photon interactionPhoton interacts with the nucleus of teh target atom causing excitiationExcited nucleus decays and emits a neutron in an attempt to maintain stability
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Photodisintegration
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Photon interaction-Dependent on electron density of material-High energy- Incident photon interacts with an outer shell electron-Electron absorbs SOME of photon's energy and is ejected from outer shell-Remaining energy creats a new photon with less energy & change in direction
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Compton Scattering
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Compton Scattering
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-Dependent on electron density of material-High energy- Incident photon interacts with an outer shell electron-Electron absorbs SOME of photon's energy and is ejected from outer shell- Leaves behind a positively charged ion-Remaining energy creats a new photon with less energy & change in direction
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Photodisintegration
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Photon interacts with the nucleus of teh target atom causing excitiationExcited nucleus decays and emits a neutron in an attempt to maintain stability
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Photoelectric effect
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-Incoming photon interacts with an electron in the inner shells of the atom-ALL energy is transferred to electron which then gets ejected from the atom- Empty space filled by outer shell electrons, losing energy in the process creating a photon- Energy of each photon equals the energy differences between the electron shells
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Coherent scatter
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-Incoming photon is absorbed by atom's electrons- Atom re-emits a second photon with the same energy as the incident photon but scattered in new direction
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Most common photon interaction in radiation therapy
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Compton scattering
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Photon interaction-Incoming photon interacts with the electromagnetic field of the nucleus, absorbed, energy is re-emitted as a negatron-positron pair, and then ejected from the atom
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Pair annihilation
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Pair annihilation
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-Incoming photon interacts with the electromagnetic field of the nucleus, absorbed, energy is re-emitted as a negatron-positron pair, and then ejected from the atom-Above 1.02 MeV-Converts energy to matter and back to energy
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Differential between the actual mass of an atom and the calculated mass of an atom since some mass is converted to energy used to hold the atom together
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Mass Defecit
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Atoms with the same number of protons, but different number of neutrons
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Isotope
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Atoms with the same number of neutrons, but different number of protons
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Istone
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Atoms with the same mass number but different atomic number
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Isobar
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State that the maximum number of electrons in the valence shell is 8
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Octet rule
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The energy needed to hold an electron in an orbital shell
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Binding energy
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Defined as the amount of radiation present per unit time per unit area perpendicular to the beam direction at point of interest.
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Beam intensity
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Beam energy based on the energy of photons in the beam
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Beam Quality
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Beam made up of photons of various energies
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Polychromatic / polyenergetic / heterogenous
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Portion of teh beam that passes through an absorber unaffected
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Transmission
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Inverse Square Law
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Intensity of a beam is inversely proportional to the square of the distance from the source of the beam
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The fractional change in beam intensity per thickness of the attenuating material due to interactions in the material
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Linear Attenuation coefficient
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Examples of Directly Ionizing Radiation
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ProtonsAlphasBetas/Electrons
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Examples of Indirectly Ionizing Radiation
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XraysGamma RaysNeutrons
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Resting Energy of Electron?Proton?Neutron?
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.511 Mev938.2 Mev939.5 Mev
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Mass of an electron?Proton?Neutron?
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SmallestMediumLargest
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How do ion chambers work?
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2 electrodes with low voltage appliedIrradiated chamber results in ion pairs which move to oppositely charged electrode and create a current measured by an electrometer
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How do GM counters work?
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A gas-filled device, high voltage applied, creates electrical pulse when radiation interacts with gas in the tube.Detect low levels of radiationDetects not measure
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Proportional counters detect?
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Able to discriminate between alpha and beta particles
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Difference between proportional and neutron detectors?
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Neutron detector is coated with boron or hydrogen
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How do TLDs work?
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Consists of crystal lattice made of lithium fluoroide.Crystals hosue electrons in valence shell, when irradiated electrons become excited and move to conducting bandOnce excitement wears off, electrons are caught in trapsTLDs are heated to release electronsRelease energy in form of a light photon
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EnergyFormula?Unit?Details?
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Ability to do work
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ForceFormula?Unit?Details?
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Mass x AccelerationNewton or kg m/s~2
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4 fundamental forces:
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Strong nuclear forceElectrostatic/Coulomb forceWeak nuclear forceGravitational force
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AreaFormula?Unit?
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Length x WidthUnit of length
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WavelengthFormula?Unit?
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W=C/vMeters
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FrequencyFormula?Unit?
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V=C/WHertz or 1/s
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Energy of photonFormula?Unit?
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E= 1.24x10~-12 MeV/m divided by wavelength in meterseV, KeV, MeV
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Characteristic Interaction
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Collision interactions involve high speed electrons giving some of their momentum to target electrons, causing ionization and voids in target atomsVoid in target atom is filled by an outer shell electronEnergy is released in characteristic radiationThis energy is difference between binding energies of the involved shells
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Bremsstrahlung Interaction
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Radiative interactions result from force of attraction between high speed electrons and atomic number target atomsAttraction of opposite charges causes high speed electrons to slow down and release energy
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Majority of radiation in radiation therapy is what interaction?
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Brems
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Characteristics of photons
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No charge, no massExponentially attenuated by matterGradual dose fall off after Dmax is reachedOffers more skin sparingUsed to treat deep seated tumorsTarget & flattening filter are in place
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Polarization voltage charge order left to right
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Ion recombinationIonization chamber regionProportional counter regionGeiger counter region
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Amount of ionization produced by photon in air per unit mass of air
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Exposure (x)
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Mean energy absorbed in a tissue or organ x quality factor for the given radiation type x weighting factor for tissue sensitivitiy
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Effective dose
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Characteristics of electrons
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Have charge and massRapid dose fall off after 90% dose levelGives a high skin doseUsed for superficial skin/shallow diseaseTarget and flattening filter retract, scattering foil in placeTissue inhomogeneties have significant impact
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(1/2)mass x velocity ^2
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Kinetic energy formula
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Units of energy
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kg meter squared/second squaredJouleErgElectron volt
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Dosimetric field size is defined as the distance between the __% isodose lines at a given depth
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50%
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Characteristics of EMR
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No chargeNo massUnaffected by electric and magnetic fieldsTravels at the speed of light in a vacuumExponentially attenuated by matter
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__?__ is defined as the maximum variation of the beam intensity in the central 80% of the beam, often measured at a depth of 10 cm and has a tolerance of +/- 3%
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Beam flatness
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Defined as the lateral distance between two specific isodose lines, often the 90% and 20% lines.
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Physical penumbra
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Characteristics of megavoltage external radiation therapy machines
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High outputSmall penumbraHigh penetrationFlat dose profilesLow skin dose
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__?__ Number determines the chemical properties of an element
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Valence
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Electron binding energy of an atom increases as proximity to the nucleus ___, mass number __, and atomic number __?
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Proximity to nucleus IncreasesMass number increasesAtomic number increases
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Photon interaction that has a threshold energy value of 1.02 MeV
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Pair production
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Photon interaction where probability increases with an increase in atomic number by z^3
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Photoelectric effect
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Photon interaction that involves an interaction between a photon and an inner shell electron
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Photoelectric effect
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An interaction between high energy photons and high atomic number material in which the atoms of the medium become unstable and emit neutrons
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Photonuclear interaction
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Photon interaction probability decreases with an increase in photon beam energy of 1/E
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Compton scatter
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The most commonly occurring photon interaction with matter in the energy range of radiation therapy
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Compton scatter
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Results in ionization or not:Compton and Photoelectric
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Results in ionization
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Results in ionization or not:Coherent and pair production
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Does not result in ionization
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Interaction involving an incoming photon that gives up some of its energy to a loosely bound electron causing ionization
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Compton scatter
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INteraction involving a low energy photon that is absorbed by an electron of an atom and is then reemitted in a new direction with the same energy as the original
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Coherent scatter
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Interaction involving the conversion of energy to matter and then back to energy
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Pair production
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Interaction that is independent of the atomic number of the absorbing material
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Compton scatter
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Quality factor of gamma rays and electrons
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1
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Quality factor of thermal neutrons
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5
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Quality factor of protons (<10MeV)
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10
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Quality factor of natural alpha particles
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20
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Dmax for 6 MV
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1.5 cm
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Dmax for 10 MV
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2.5 cm
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Dmax for Co-60
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.5 cm
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Dmax for 25 MV
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5 cm
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Dmax for 4 MV
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1 cm
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Helium nuclei (2 protons bound by 2 neutrons)
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Alpha particle
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The sum of the protons and the neutrons.
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Atomic mass number
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The number proteins in a nucleus
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Atomic Number
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The energy that must be added to an electron in order to remove it from the atom
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Binding energy
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Electrons/positrons emitted by the nucleus
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Beta (plus/negative) Particles
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When an electron interacts with the positive charge of an atomic nucleus.
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Bremsstrahlung
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Describe Bremsstrahlung
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During a Bremsstrahlung interaction the electric field of the nucleus causes the electron to change direction or velocity. This change causes a loss in kinetic energy. Since the lost energy must go somewhere it creates an xray photon.
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When an electron is removed from the atom
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Ionization
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When an electron in a lower shell is moved to a higher shell
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Excitation
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Describe characteristic radiation
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In a characteristic interaction enough energy is given to an electron to remove it from the atom (ionization) To replace the empty space from that electron, an outer shell electron will fill the vacancy. The potential energy between where the electron started and where it will end up is given off as a photon. An xray photon results from a large difference and a light photon results from small difference.
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Energy of motion
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Kinetic energy
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Stored energy
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Potential energy
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Causes matter to accelerate
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Force
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SI unit of frequency
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Hertz
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Same number of protons
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Isotope
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Same number of neutrons
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Isotone
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Energy deposited into a medium per unit length of travel by ionizing radiation as it passes through the medium
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Linear energy transfer
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Speed of light
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3x10*8 m/s |
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Energy in eV
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1.24 x 10*-6 ev/m divided by wavelength in m |
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Metric conversions |
Nano micro milli centi deka...kilo mega giga tetra |
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Resting energy of an electron
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.511 MeV
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Resting energy of an proton
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938.2 MeV
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Resting energy of a neutron
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939.5 mev |
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Difference between mass of an atom and sum of the weights of the atom's subatomic particles.
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Mass deficit
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Same mass number but different atomic number
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Isobar |
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Same atomic number and mass number but unstable
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Isomer
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Octet rule
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No more than 8 electrons can be in the valence orbital shell
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Number of electrons in the outer most orbital shell
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Valence
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100 rad = ? Gy
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1 Gy = ? rad
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Electric potential is measured in ...?
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Volt
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100 rem = ? Sv
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1 Sv= ? rem
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__________J = 1eV
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1.621 x 10^-19
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Force = ? 2 labels
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Newton or kg m/s^2 |
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Frequency = ? 2 labels
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Hertz or cycles/sec
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Energy = ? 2 labels
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Joule or kg m^2/s^2
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1 Angstrom = ? meters
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10^-10 meters = ? Angstrom
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Celsius =
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5/9(F-32)
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Fahrenheit
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(9/5C)+32
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1 Roentgen = ? C/kg
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2.5x10^-4 C/kg =?
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Linear attenuation coefficient formula
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.693/HVL
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Natural log base = ?
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2.718
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Formula for activity =?
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A= A0e ^(-.693)(t)(T1/2)
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During characteristic radiation, excess energy can knock out one of the outer electrons from the atom, this electron is called what?
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Auger electron
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Electromagnetic Radiation
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Gamma rays, uv light, visible light, infrared light, microwaves, radio waves
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Probability per unit thickness that any one photon will be attenuated.
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Linear attenuation coefficient
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Combination of a beam's first HVL and the ratio of the first to the second HVL
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Homogeneity Coefficient
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