radiation physics Flashcards
In what part of the EM spectrum do you find X-rays?
In the ionising radiation sector.
Describe x-rays in terms of their wavelength and energy.
SHORTER WAVELENGTHS with HIGHER ENERGY.
What is the x-ray tube target made out of?
Tungsten
Why is the x-ray tube target made out of tungsten?
Due to its high melting point.
What is the x-ray tube surrounded by?
A glass envelope creating a vacuum.
What potential difference is used?
70 kv
What happens to the electrons in the continuous spectrum?
The incoming electrons are slowed down and deflected to varying degrees, producing a complete range of x-ray photon energies.(the continuous spectrum is the CONTINUOUS line)
Where on the graph is the highest energy of x-rays to be produced?
Where the line hits the X-axis but this is 0.
What is the characteristic spectrum?
Photon energy emissions characteristic of the tungsten target.
What element is used to selectively filter the beam?
Aluminium
What is the purpose of the aluminium filter?
To absorb the low energy, harmful x-rays so they are not absorbed by the body.
What determines the quality of the x-ray beam?
Voltage (kV)
Which factor affects the film contrast?
Voltage (kV)
Which factor determines the QUANTITY of the x-ray photons?
time and current (mA)
What occurs during the photoelectric effect?
- The x-ray hits the electron and causes it to shoot off.
- Electron is ejected and this is the photoelectron.
- The vacancy from the ejected electron is filled by an electron dropping in from the outer shells.
- Excess energy is released via characteristic radiation.
Why are photoelectrons damaging?
Because of the impact it may have elsewhere in the body.
What occurs during Crompton scatter?
The x-ray photon interacts with an outer electron, changes direction (scatters) and loses energy.
Where does Crompton scatter occur?
Not dependent on any factors - OCCURS IN ALL TISSUES EQUALLY.
Which interaction is responsible for producing contrast?
PHOTOELECTRIC EFFECT - produces contrast between the different atomic numbers.
Which 2 types of abnormality are caused by direct damage?
- Radiation induced malignancies (somatic cells)
- Congenital abnormality (genetic cells)
How does indirect damage occur?
Electron interacts with a water molecule, producing harmful free radicals.
Deterministic effects on the oral cavity.
- Mucositis
- Loss of taste
- Xerostomia
- Radiation-induced caries
- Tooth defects if developing teeth are irradiated
Radiation Absorbed Dose
Amount of energy absorbed from the radiation beam per unit mass of tissue.
(amount coming out of the x-ray tube)
Equivalent Dose
(type x = type y)
Allows the radiobiological effectiveness of different types of radiation to be compared.
Effective Dose
Allows investigations of different parts of the body to be compared by converting all doses to an EQUIVALENT WHOLE BODY DOSE.
