10. Interaction of Radiation with Matter Flashcards
is defined as the rate of emitted energy from unit surface area through unit solid angle
Radiation Intensity
The total reduction in the number of x-rays remaining in an x-ray beam after penetration through a given thickness of tissue
Attenuation
is the product of absorption and scattering
Attenuation
is an all-or-none condition for an x-ray
Absorption
is a quantity that characterizes how easily a material or medium can be penetrated
by a beam of light, sound, particles, or other energy or matter.
Attenuation Coefficient
The attenuation coefficient is also called
linear attenuation coefficient,
narrow beam attenuation coefficient, or
absorption coefficient
means that the beam is quickly “attenuated” (weakened) as it passes through the medium
large attenuation coefficient
means that the medium is relatively transparent to the beam
small attenuation coefficient
The difference in x-ray interaction
Differential Absorption
Increases as the kVp is reduced
Differential Absorption
Differential absorption and attenuation of the x-ray beam depend on the following factors:
o The atomic number (Z) of the atoms in tissue.
o The mass density of the atoms in tissue.
o The x-ray energy.
The Thickness of an absorber needed to reduce the intensity of the x-ray beam into half of its original value
Half-Value Layer (HVL)
The fraction of the beam that penetrates the block
Transmission Fraction
TF = 2^–n
Where n =
block thickness/half value thickness
X-ray Interaction Mechanism
- Coherent Scattering
- Compton Scattering
- Photoelectric Effect
- Pair Production
- Photodisintegration
Energies below approximately 10 keV
Coherent Scattering
Coherent Scattering sometimes called
Classical scattering or Thompson scattering, Rayleigh Scattering
No ionization
Coherent Scattering
is an interaction between low-energy x-rays and atoms.
Classical scattering
The x-ray loses no energy but changes direction slightly.
Classical scattering
The wavelength of the incident x-ray is equal to the wavelength of the scattered x-ray
Classical scattering
the incident x-ray interacts with an outer shell electron and ejects it from the atom,
thereby ionizing the atom
Compton Effect
The ejected electron is called a
Compton electron or a secondary electron
occurs between moderate-energy x-rays and outer-shell electrons.
Compton Effect
It results in ionization of
the target atom, change in direction, and reduction in x-ray energy.
Compton Effect
the wavelength of the scattered x-ray is greater than that of the incident x-ray.
Compton Effect
The x-ray continues in a different direction with less energy
Compton Effect
The probability of the _______ is inversely proportional to x-ray energy (1/E) and independent of atomic number
Compton Effect
Interacts with inner shell electrons
Photoelectric Effect
X-rays are absorbed
Photoelectric Effect
The electron removed from an atom is called
photoelectron
is total x-ray absorption
Photoelectric Effect
The probability of the ________ is inversely proportional to the third power of the x-ray energy (1/E)^3
Photoelectric Effect
The probability of \_\_\_\_\_\_\_ is directly proportional to the third power of the atomic number of the absorbing material (Z^3)
Photoelectric Effect
Incident electron interacts with the nuclear field
Pair Production
The interaction between the x-ray and the nuclear field causes the x-ray to disappear, and in its place, two electrons appear, one positively charged (positron) and one negatively charged (electron)
Pair Production
positively charged
positron
negatively charged
electron
Occurs above 1.02 MeV
Pair Production
Occurs with x-ray energies above 10 MeV
Photodisintegration
The nucleus is raised to an excited state and instantly emits a nucleon or other nuclear fragment
Photodisintegration
it means there is decrease in x-ray quantity or the amount of the x-ray beam
Attenuation
The ______ the linear attenuation coefficient, the ______ capability of the material to absorb radiation. Organizing radiation.
greater,
greater
type of interaction occurs when there is no interaction
Excitation
the incoming electron does not possess enough energy to remove any electron the atom; the atom will just raise to the higher energy state and eventually return to its normal state; in the process,
Excitation
In Excitation, ______ is being emitted but there is no removal of electrons involve.
Infrared Radiation
The incident photon strikes the atom but its energy is not enough it is deflected; atoms are just trembles or shaken and eventually return to normal
Classical scattering
Occurs when the energy of the incoming electron is about approximately 20 or 27 up to 37 kEv
Compton Effect
The energy of the incoming electron is not that much but it’s enough to produce ionization in outer shell electrons; the ejected electrons is what we call the ______, it will be scattered. If the scattered electrons still have enough energy, it will continue ionizing others till the energy is gone, just like the billiard-ball analogy.
Compton Electron
Compton effect SI Unit:
kEv
X-rays are scattered
Compton Electron
Interacts with outer shell
Compton Electron
If you increased the kVp, the probability of Compton effect will
decrease
The incoming electron will remove the inner shell electron; the ejected electron is known as PHOTOELECTRON, if it has enough energy, it will ionize other atom, it will strike and eject other electron, the second electron that will be ejected is what we called
Auger Electron
In the photoelectric effect once the inner shell electrons have been ejected; there are 2 possible ways:
1) electrons drops the fill of vacancy of the emitting photon or
2) the energy is transfer to outer electron and ejects it
The higher the atomic number the _____ the chance of having photoelectric effect; _____ chance of having an absorption.
greater,
greater
Incoming electron interacts with the nuclear field; the atom will be divided into a positive charge and negative charge both of the particles possess 0.511 MeV a total of 1.02 MeV, in order to create pair production, the energy of the projectile electron must be equal or greater than 1.02 MeV.
Pair Production
does not occur in diagnostic radiography, it only occurs in PET imaging or nuclear medicine
Pair Production
are the only interaction contributes in diagnostic radiography
Photoelectric Effect and Compton Effect
Occurs in nuclear bomb explosion
Photodisintegration
Incoming electron interacts with the nucleus and disappear in nuclear fragments and scattered away
Photodisintegration
Indicates the ability of material to attenuate
Linear Attenuation Coefficient
is the total reduction of
radiation intensity
Attenuation
The type of interaction that will occur in coherent scattering is
Excitation
Does not contribute to the formation of the image
Coherent Scattering
is not capable of removing the electron in the shells
Low energy
99% of coherent scattering is
heat or infrared radiation
The more the energy is decreased, photoelectric effect ______
increases
The term “_____” is used because the types of substance is an aggregation of
different types of element.
Effective
Fat effective atomic number
6.3
Soft tissue effective atomic number
7.4
Lung effective atomic number
7.4
Bone effective atomic number
13.8
Air effective atomic number
7.6
Iodine effective atomic number
53
Barium effective atomic number
56
Concrete effective atomic number
17
Molybdenum effective atomic number
42
Tungsten effective atomic number
74
Lead effective atomic number
82
Rhodium atomic number
45
Rhenium atomic number
75
Calcium atomic number
20
Hydrogen K-shell electron binding energy
0.02
Carbon K-shell electron binding energy
0.3
Nitrogen K-shell electron binding energy
0.4
Oxygen K-shell electron binding energy
0.5
Aluminum K-shell electron binding energy
1.6
Calcium K-shell electron binding energy
4.1
Molybdenum K-shell electron binding energy
19
Rhodium K-shell electron binding energy
23
Iodine K-shell electron binding energy
33
Barium K-shell electron binding energy
37
Tungsten K-shell electron binding energy
69
Rhenium K-shell electron binding energy
72
Lead K-shell electron binding energy
88
