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X-RAY INTERACTIONS W

H I X-RAY INTERACTIONS WITH MATTER & FILM

QuestionAnswer
will lose all of its kinetic energy and deposit in a shell on an atom COMPTON EFFECT
classical scattering COHERENT SCATTERING
general graying of the radiograph which reduces contrast FOG
Incident x-ray photon interacts with target atom COHERENT SCATTERING
Occurs with x-rays of moderate energy COMPTON EFFECT
Occurs with photons less than 10 keV COHERENT SCATTERING
Coherent scattering contributes to Fog
No ionization occurs COHERENT SCATTERING
Thompson scattering COHERENT SCATTERING
Also known as Compton scattering COMPTON EFFECT
occur most common Compton and Photoelectric effects
This is an absorptive phenomena PHOTOELECTRIC EFFECT
Electron that is removed from the atom is termed a photoelectron
X-ray photon is not scattered but is absorbed PHOTOELECTRIC EFFECT
X-ray photons undergo an ionizing interaction with inner shell electrons PHOTOELECTRIC EFFECT
They are more tightly bound PHOTOELECTRIC EFFECT
an absorption phenomenon PHOTOELECTRIC EFFECT
The photoelectron escapes with kinetic energy equal to the difference between the energy of the incident x-ray photon and the binding energy of the electron PHOTOELECTRIC EFFECT
atom is excited and releases the excess energy as a scattered x-ray COHERENT SCATTERING
Xray photon of the same energy but in a different directionà scatter photon
Causes the target atom to get excited and go to a higher state COHERENT SCATTERING
approximately 5% of photons undergo coherent scattering At 70 kVp
Incident x-ray and scattered x-ray have the same wavelength and the same energy COHERENT SCATTERING
Incident x-ray photon interacts with an outer shell electron of the target atom and ejects the electron ionization
ionization COMPTON EFFECT
Scattered photon can be scattered in any direction including 180 degrees backwards backscatter radiation
Usually scattered x-ray photon retains most of the energy of the incident x-ray COMPTON EFFECT
looses the outer shell electron COMPTON EFFECT
Backscatter radiation can come from the patient, the cassette, or the tray
causes radiographs to look duller and flatter Compton effect
electron has some kinetic energy after it is ejected COMPTON EFFECT
hazardous to x-ray technicians and doctors backscatter
the material in which x-ray photons or light photons emitted from the screens form the radiographic image Emulsion
homogenous mixture of gelatin and silver halide crystals Emulsion
foundation of the film FILM BASE
Provides rigid structure but is flexible and fracture resistant FILM BASE
Film base is made of polyester
added to the base to tint the film Blue dye
reduces eyestrain Tinting
Original base glass plates
In the mid 1920’s a safety base film began to be used cellulose triacetate
The photon is directly absorbed by the nucleus PHOTODISINTEGRATION
The nucleus is excited and instantaneously releases a nucleon or other nuclear fragment PHOTODISINTEGRATION
The electron produced falls into a vacant shello PHOTODISINTEGRATION
the quantity of matter per unit volume MASS DENSITY
When the mass density is doubled x-ray interaction is doubled
The radiographic image results from approximately 1% of the x-rays
x-ray incident on the patient that reach the film Less than 5%
The positron combines with another electron and energy is produced annihilation radiation
X-ray photon goes close to the nuclear field of the an atom and disappears PAIR PRODUCTION
Occurs with high energy x-ray photons – not diagnostic x-rays PAIR PRODUCTION
Photon reduction is done exponentially ATTENUATION
The reduction of the number of electrons in a beam ATTENUATION
The half value layer for soft tissue is 5 cm
x-rays that remain after the useful beam exits the patient Remnant beam
Image forming x-rays interact with image receptor
The thickness of radiographic film is between 150-300 micrometers
Usually the emulsion is on both sides of the base double emulsion
Two basic parts of film film base and emulsion
protective covering made of gelatin supercoat
binds the emulsion to the base adhesive
chemical contaminant added to the crystal silver-gold sulfide
silver-gold sulfide is called sensitivity speck
determined by the process of how the silver halide crystals are formed Film speed, contrast(gray scale), and resolution(clearness)
During the exposure, photoelectrons and silver ions are attracted to the sensitivity center and these form silver metal (the latent image)
The blackness on the Xray film is due to Silver metal
image after the exposure latent image
image during chemical processing manifest image
Only two interactions are important to radiology Compton effect and the photoelectric effect
X-rays that undergo the photoelectric effect produce diagnostic information
X-rays that do not reach the film give an opaque area
In an optimally exposed film ________ are collected at the sensitivity center 4-10 silver atoms
During processing, more silver atoms collect at the latent image center to form the radiographic image (manifest image)
The collection of silver atoms is a black grain
the functional part of the Xray emulsion Silver halide crystals
the support medium for the silver halide crystals gelatin
x-rays emerging from the tube that will be incident on the patient Useful beam
Remnant beam consists of x-rays and scattered x-rays
produced after a photoelectric interaction characteristic xray
Ejection of a k shell electron from an incident x-ray causes an electron from an outer shell (usually the l shell) to drop in and fill the closer shell PHOTOELECTRIC EFFECT
Interactions with low atomic number atoms (low binding energy) results in the photoelectron having large amount of kinetic energy
As x-ray photon energy increases the photoelectric effect decreases
As atomic number increases the photoelectric effect increases
can only occur if the incident photon has enough energy to cause ionization photoelectric effect
Created by: hakrrins
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