Interaction Of Radiation With Matter Flashcards
How are X-Ray photons creates?
Interaction of energetic electrons with matter at the atomic level
How do photons end their lives?
Transferring their energy to electrons contained in matter
What are X-day interactions important for?
Diagnostic examination
What does the selective interaction of X-day photons with structure of human body produce?
Image
What does the interaction of photons with receptor concert?
X-rah or gamma image into one that can be viewed and recorded
What are the possible fates that awaits each photon as x-ray beam of gamma radiation passes through an object?
- It can penetrate the section of matter without interacting
- It can interact with the matter and be completely absorbed by depositing its energy
- It can interact and be scattered or deflected from its original direction and deposit part of its energy
What does photons entering the human body do?
- Penetrate
- Be absorbed
- Produce scattered radiation
What are two kinds of interaction through which photons deposit their energy?
- The photon loses all its energy
2. The photon loses a portion of its energy and the remaining energy is scattered
What are the two steps of photoelectric interaction?
- The photon transfers its energy to the electron
2. The depositing of the energy in the surrounding matter by the electron
Where does photoelectric interaction usually occur?
Electrons that are firmly bound to the atom
When is photoelectric interaction most probable ?
When the electron binding energy is only slightly less than the energy of the photon
When is photoelectric interaction possible?
When the photon has sufficient energy to overcome the binding energy and remove the electron from the atom
What are the two parts that the photons energy is divided into?
- A portion of the energy is used to overcome the electrons binding energy and remove it from the atom
- The remaining energy is transferred to the electron as kinetic energy and is deposited near the interaction site
What does the photoelectric interaction create?
Vacancy in one of the electron shells, an electron moves down to fill in
What often produces a characteristic x-ray photon?
The drop in energy of the filling electron
What does the energy of the characteristic radiation depend on?
Binding energy of the electrons involved
What is referred to as fluorescent radiation?
Characteristic radiation initiated by an incoming photon
What is fluorescence?
A process in which some of the energy of a photon is used to create a second of less energy
Converts x-rays into light photons
What does the fluorescent radiation in the form of light or x-rays depend on?
Binding energy levels in the absorbing material
What is a Compton interaction?
Only a portion of the energy is absorbed and a photon is produced with reduced energy
What is the most significant object producing scattered radiation in an x-ray procedure?
The patients body
What becomes the actual source of scattered radiation?
The portion of the patients body that is within the x-day been
What are two undesirable consequences of Compton interaction?
- The scattered radiation that continues in the forward direction and reaches the image receptor decreases the quality of the image
- The radiation that is scattered from the patient is the predominant source of radiation exposure to the personnel conducting the examination
What is pair production?
Photon-matter interaction that is not encountered in diagnostic procedure because it can occur only with the photons with energies in excess of 1.02 MeVvv
What happens in a pair-production interaction?
The photon interacts with the nucleus in such a manner that its energy is converted into matter
What does pair production interaction produce?
A pair of particles
- Electron
- Positively charged positron
- same mass each equivalent to a rest mass energy of 0.51 MeV
What are the two phases of electron interactions?
- One-shot interactions between photon and an electron in which all or a significant part of the photon energy is transferred
- Transfer of energy from the energised electron as it moves through the tissue
What are the several types of radioactive transition that produce electron radiation?
- Beta radiation
- Internal conversion electrons
- Auger electrons
In Compton interaction, what does the relationship of the electron energy to that of the photon depend on?
- Angle of scatter
2. Original photon energy
What happens as the electrons leave the interaction site?
Immediately begin to transfer their energy to the surrounding material
When does ionisation occur?
If the force on an electron is sufficient to remove it from its atom
What is generally referee to as its range?
The total distance an electron travels in a material before losing all its energy
What are the two factors that determine range?
- Initial energy of the electrons
2. Density of the material
What is one important characteristic of electron interactions ?
All electrons of the same energy have the same range in a specific material
What is range of electron radiation in material such as tissue?
Fraction of a millimetre
What does a fraction of a millimetre indicate?
All electron radiation energy is absorbed in the body very close to the side containing the radioactive material
What is known as the linear energy transfer (LET)c
The rate at which electron transfers energy to a material
What is LET expressed in terms of?
The amount of energy transferred per unit of distance travelled
What is LET generally inversely related to?
Electron velocity
What happens when radiation electron loses energy?
- Velocity decreases
2. Value of LET increases until all its energy is dissipated
What is often related to LET of the radiation?
The effectiveness of a particular radiation in producing biological damage
What are the two phases between positron and matter?
- Ionisation
2. Annihilation
What is the energy equivalent of one electron or positron mass?
511 keV
What is attenuation
The interactions, either photoelectric or Compton, remove some of the photons from the beam
What is the linear attenuation coefficient ?
Actual fraction of photons interacting per 1-unit thickness of material encountered by the photons rather than in terms of distance
What does the linear attenuation coefficient values indicate?
The rate at which photons interact as they move through material and are inversely related to the average distance photons travel before interacting
What is the rate at which photons interact determined by?
Energy of the individual photons and the atomic number and density of the material
What is the mass attenuation coefficient ?
The rate of photon interactions per 1-unit area mass
What has a direct effect on linear attenuation coefficient values?
Material density
What does the total attenuation rate depend on?
Individual rates associated with photoelectric and Compton interactions
What are the factor that determines if a photon will interact as it travels a 1-unit distance
- Concentration or density of electrons in the material
