Flashcards in X-Ray Interaction with Matter Ch 9 Deck (45):
How many types of interactions are there with matter?
2. Photoelectric effect
4. Pair Production
What happens to the x-ray beam as it passes through matter?
What is penetration?
Photon passes through unchanged to produce a black area on the image receptor
What are the two factors that allow penetration?
1. x-rays are electrically neutral
2. Atoms consist mainly of empty space
The probability of penetration increases with
1.Higher quantity of short wavelength radiation
2. Less tissue thickness
3. Lower tissue density (z)
High frequency is ____ wavelength.
How do you get a higher quantity of short wavelength radiation?
-Increase atomic number (z) of the target
What is attenuation?
-Exposure rate is decreased
-X-ray beam can be absorbed or scattered
In attenuation (absorption), the exposure rate is decreased due to what (3) factors?
1. Photon is absorbed in the body producing secondary radiation (characteristic)
2. Part of the body undergoes a change in direction resulting in scatter radiation (Compton or Coherent)
3. Inverse Square Law
The probability of attenuation increases with...
-Higher quantity of long wavelength radiation
-Increased tissue thickness
-Higher tissue density
The ______ the wavelength the greater the probability of photons interacting with one of the electrons in the shells surrounding the nucleus of an atom in the body.
What is the photoelectric effect?
-The photon entering the body being completely absorbed
What are the results of the photoelectric effect?
-Characteristic radiation (true secondary radiation)
-Photoelectron (Neg ion)
*K shell electron that was kicked out
*Atom that was left behind
If you do not have photoelectric effect, you do not have an...
What two things together make up an ion pair?
Photoelectron (Neg ion)
The probability of the photoelectric effect increase with what?
- Atoms with a high atomic number
- Incident photon having keV = or higher than the binding energy of the inner shell electron
- Lower energy x-ray photons
What is Compton Interaction?
What is another word for Compton Interaction?
What are the results of Compton Interactions?
*Recoil Electron- Neg ion
The energy of the scattered photon will be dependent on what?
It's angle of deflection
If a photon just glances off the e- and is scattered by a small angle, it will retain a ____ _____ of it's original angle.
The larger the angle, the ____ energy it will retain and the ____ energy is transmitted to the recoil e-.
The scattered photon will retain up to ____ of it's original energy.
What happens to a scattered photon (produced in the body?)
-It can be transmitted through matter
-It can be absorbed in a photoelectric interaction with another atom
- It may result in further Compton interactions
Where is a scattered photon produced?
In the body
The ______ of Compton scatter is a complex function of the energy of the incident x-ray.
In general, the probability of the Compton Effect _____ as x-ray energy increases.
As kVp is increased the probability of Compton Interaction...
The probability of Compton scattering does not depend on the ___ ____ of the atom.
With higher kVp, the Compton photons that do occur have ____ energy.
With higher kVp, the Compton photons that do occur have more energy and move in a _____ direction.
Forward (toward the IR)
(Angle of deflection is small)
The photons that increase the likelihood of their passing through the body and reaching the image receptor constitutes the scatter radiation, which in radiography impairs the image _______ by an overall fogging effect.
What is the fogging effect?
A form of noise that degrades recorded detail
Even though fog is on the image, do you still have the detail of the image?
Yes, you just can't see it very well.
Compton scattering ______ image contrast.
The photoelectric effect is _____ x-ray absorption.
What two interactions with matter are important in making an x-ray image?
Compton scattering and Photoelectric effect
Do x-rays have short or long wavelengths?
In Compton scattering, the incident x-ray interacts with an outer shell electron and ____ it from the atom.
What is the ejected electron in Compton scattering called?
Scattered x-rays provide ___ useful information on the radiograph.
A _____ amount of radiation can be scattered from the patient during fluoroscopy.
________ radiation during fluoroscopy is the source of most of the occupational radiation exposure that radiographers receive.
What earned Albert Einstein the nobel peace prize in 1921?
The discovery of the photoelectric effect