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Beam Characteristics
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37
Physics
Professional
03/12/2013

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Term
angstrom
Definition
unit of length equal to 10^-10 (one tenbillionth of a meter)
used for wavelength
Term
frequency
Definition
number of complete oscillations per second of an electromagnetic wave
Term
photon
Definition
the smallest quantity of any type of electromagnetic radiation
Term
quantum
Definition
a small bundle of photon energy
Term
wavelength
Definition
distance between two successive similar points on a wave
length of one cycle
Term
electromagnetic radiation
Definition
wavelike fluctuations of electric magnetic fields set up in space by oscillating electrons
includes xrays gammarays, etc
Term
density
Definition
the degree of blackening of a radiograph resulting from radiation exposure and processing
Term
clear area
Definition
low optical density
Term
black area
Definition
represents high optical density
Term
factors that affect density
Definition
MAS
time
distance
kvp
film processing
filtration
patient factor
heel effect
intensifying screens
Term
remnant radiation
Definition
also called exit radiation
radiation that exits the anatomic part and exposes the radiographic screens placed in the cassette
Term
composition of xray beams (electromagnetic radiation)
Definition
white light
UV light
infrared
microwaves
radiowaves
Term
properties of electromagnetic radiation
Definition
highly penetrating, invisible rays
electrically neutral
polyenergetic
liberates minute amounts of heat
travels in straight lines at the speed of light
ionizes gasses indirectly
causes flourescence of certain crystals
cannot be focused by a lens
affects photographic film
produce scattered radiation
Term
speed of light
Definition
3 x 108 m/s
186,000 miles per second in vacuum
Term
three regions of importance to radiography
Definition
visible light
radiofrequency
xradiation

only difference is in frequency and wavelength
Term
velocity= frequency x wavelength
Definition
c= frequency x wavelength
Term
decrease
Definition
an increase in frequency would cause a ____ in wavelength
Term
photon energy
Definition
directly proportional to the photon frequency
Term
the constant of proportionality
Definition
Plank's constant
symbolized by h
4.15 x 10^-15 ev/s
Term
the relationship between energy and frequency
Definition
E= h x f
Term
the relationship between energy and frequency
Definition
E= h x f
Term
inverse square law
Definition
radiation intensity from an xray tube varies inversely with the square of the distance from the target
I1/I2=(D2)^2/ (D1)^2
Term
incident
Definition
falling upon or striking
Term
scatter
Definition
involves a change in direction
Term
transmission of a photon
Definition
the dark areas on a radiograph represent the area where the xray beam hit the film unaltered
Term
classical scatter
Definition
unmodified scatter/thompson effect/ coherent scatter
low every photon is absorbed by an outer shell electron and becomes excited, photon released by atom with same amount of energy as incident photon and goes on a random course
Term
compton effect
Definition
moderate to high energy photon interacts with outershell electron, outershell electron is ejected, photon is scattered with less energy and less penetration
Term
almost the entire scatter that we encounter in radiology
Definition
compton scattering
Term
fogging
Definition
a form of noise that degrades the image
caused by compton scattering
Term
photoelectric effect
Definition
moderate to high energy photon interacts with inner shell electrons
inner shell electron is ejected
most probably when electron binding energy is only slightly less than the energy of the incident photon
varies directly with atomic number of irradiated tissue
Term
4-6
Definition
PE is ___times more likely in bone rather than soft tissue
Term
pair production
Definition
high energy photon interacts with nuclear electrostatic field
occurs with photon energy of at least 1.02 MeV
Term
negatron
Definition
negative charge
eventually becomes an orbital electron
Term
positron
Definition
positively charged that eventually combines with a free electron and forms positronium that only exists for 10^-10 seconds
Term
annihilation reaction
Definition
thee second stage of pair production
positronium disappears, giving rise to two photons, each having an energy of .51 MeV
Term
photodisintegration
Definition
high energy photon interacts with the nucleus of an atom
occurs with photon energy above 10 MeV
Term
differential absorption
Definition
only three important xray interactions
compton effect
photoelectric effect
transmission of photon
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