X-RAYS Flashcards
(24 cards)
What kind of wave are Xrays
electromagnetic waves
How are they produced?
When charged particles have a change in velocity through deceleration in matter
n.b: different from gamma rays since they originate from nuclear processes
Characteristics
1.Have a high penetration depth
2.Travel in straight lines with negligible scattering
3.Not deflected by magnetic fields
4.Diffracted by crystals
5.Classsified as ionising radiation
Braking radiation
Arises from the deceleration of electrons in the electric field of the anode’s atomic nuclei.
its continuous
Characteristic radiation
Results from electronic transitions that occur when an inner-shell electron is ejected from an atom.
How does anode voltage affect?
Determines the maximum photon energy and minimum wavelength.
how does anode material affect
Defines the characteristic peaks in the X-ray spectrum.
how do filteres affect?
Remove lower-energy photons, hardening the beam
how does anode cuurent affect?
Determines the beam intensity.
how does anode angle affect?
Affects the geometry of the emitted beam and the effective focal spot size.
formula for efficiency
The efficiency of X-ray production is typically very low (on the order of 1%) and can be expressed as:
η=K⋅Z⋅V
where
K = A constant (depends on the system, typically around 10⁻⁹)
Z = Atomic number of the anode material (e.g., Z = 74 for tungsten)
V = Anode voltage (in volts)
so Efficiency is the ratio of X-ray energy output to the input kinetic energy of electrons.
formula of power of the braking radiation
Z⋅I⋅V^2
where:
Z = atomic number of the anode material
I = tube current
V = anode voltage
TRUE or FALSE
For a given layer thickness, the lower the attenuation coefficient of the material, the less the intensity of the X-rays passing through the sample.
False;
The higher the attenuation coefficient, the less the intensity of transmitted X-rays.
T or F;
For diagnostic X-rays, the mass attenuation coefficient of human bone tissue is less than that of fat tissue.
F
Bone tissue has a higher mass attenuation coefficient than fat tissue (due to higher atomic number and density).
T or F:
Tissue contrast is the relative difference between the X-ray intensity transmitted through the background tissue and the actual tissue.
true
T or F:
The mass attenuation coefficient is defined as product of the attenuation coefficient and the density of the material.
F;
It is defined as the attenuation coefficient divided by the density of the material.
T or F:
Compton effect refers to the process where X-ray photons are scattered inelastically by electrons with a loss of energy.
True
T or F:
Coherent scattering refers to the process where X-ray photons knock electrons out of the outer shells of atoms.
False;
That describes the photoelectric effect. Coherent scattering involves no energy transfer and no electron ejection.
True or False;
In water, X-rays in the medium energy range (20 keV–1 MeV) are attenuated almost exclusively by pair production.
False
In this energy range, Compton scattering dominates. Pair production only occurs above 1.022 MeV.
T or F:
Photoelectric absorption does not depend on the atomic number of the absorbing material, so low-energy X-rays are excellent for diagnostic purposes.
False
Photoelectric absorption strongly depends on the atomic number (∝ Z³), which is exploited in diagnostic imaging.
Coherent scattering
An elastic scattering event where the photon changes direction but maintains its energy.
~E^−1
~Z^2
range: 1–20 keV
Compton scattering
The photon transfers part of its energy to a loosely bound electron.
E^-1
Z dependence is negligble
Range;30 keV–20 MeV
Photoelectric current
The photon transfers all of its energy to an inner-shell electron.
E^-3
Z^3
1–30 keV
Pair production
At energies above 1.02 MeV, photons generate electron–positron pairs.
E
Z^2
energy range > 20 MeV
