Basic Physics Concepts Flashcards
What is the basic unit of energy?
Joule [J]
electron-volt is also commonly used in radiology
What is the basic unit of electric charge?
coulomb [C]
What is the basic unit of power?
watt [W]
what is the basic unit of absorbed dose of ionizing radiation?
Gray (Gy)
j/kg
What is a Gray [Gr]?
The basic unit of absorbed dose of ionizing radiation
What is a sievert?
A unit for the ‘health effect of ionizing radiation on the human body’.
Are x-rays higher or lower frequency than visible light?
higher
In electromagnetic radiation, how are the directions of these fields related to each other:
- magnetic field
- electric field
- the direction of propagation/ movement?
They are all at 90 degrees to each other
What is an electron-volt [eV]
The quantity of (kinetic) energy an electron would have if accelerated over 1V.
Equivalent to 1.6 x10^19 J
What is the difference between Gamma rays and X-rays?
Gamma rays are produced in the nucleus by nuclear de-excitation
X-Rays are produced in the atomic shell by atomic de-excitation
When talking about the characteristic of different elements/ atoms, what do the letters ‘Z’ and ‘A’ normally refer to?
Z = atomic number = number of protons A = mass number = number of protons + number of neutrons
Which electron shell is on the inside of an atom?
the k shell
In X-ray production:
Is the cathode or anode the filament or target?
Cathode = filament Anode = target
What are typical voltage difference between the filament and the target in x-ray production?
50-150kV
What are the two types of radiation produced in x-rays?
Continuous radiation (Bremsstrahlung radiation) Characteristic radiation
What is Continuous radiation also known as?
Bremsstrahlung radiation?
What does Bremsstrahlung radiation mean in german?
Braking radiation
What occurs to create Bremsstrahlung radiation?
an electron swerves around the nucleus and loses some speed,
the energy lost by this swerve is released as a photon/ x-ray
Why is Bremsstrahlung radiation called ‘Continuous Radiation’
The energy of x-rays produced can be anywhere from 0 to whatever the maximum keV of the electrons was.
This gives a continuous spectrum of radiation (although it’s not all in equal amounts.
How does characteristic x-ray radiation occur?
Produced when an electron is knocked out of a shell and then another electron falls down into that shell, releasing it’s extra energy when doing so in the form of an x-ray
Why is characteristic x-ray radiation, characteristic?
X-ray photons have unique (discrete) energy values which are characteristic of the target atom
Depends on the difference in binding energy between the different electron shells
Does increasing kVp affect beam quality or quantity?
Both
What is Half Value Layer?
The thickness required to reduce beam intensity by 50%
Does the anode material affect the beam quality of quantity?
Both
How does the conversion efficiency of energy into continuous spectrum x-rays change with an increasing atomic number of the anode material?
The conversion efficiency increases as the atomic number increases.
The intensity of x-rays is approximately proportional to the atomic number.
What stops electrons from diverging as they travel from the cathode to the anode in x-ray production?
The focusing cup
What is the electrical potential of a focusing cup?
the same negative potential as the filament
How do x-ray machines avoid overheating of the anode?
A rotating anode,
so that no one physical spot has too much of the current flow through it.
Further enlarging the area hit by having it at an angle
Also cooling oil etc
What is a focal spot in x-ray generation?
The point where x-rays are emitted from?
What is the Line-Focus Principle in x-ray generation?
The size of the effective focal spot can be smaller than the size of the actual focal spot if the anode is at a sharp angle.
What is the ‘Anode Heel Effect’
If the anode where x-rays are produced is at an angle then there will be an uneven distribution of x-rays.
The x-rays are usually not produced at the surface of the anode, and so some will have to travel through more metal to get out of the anode.
Due to the ‘Anode Heel Effect’, are x-rays usually more pronounced on the anode or cathode side of x-ray films?
Cathode side,
Less intense towards the anode side
What is collimation of x-rays?
The x-ray field is limited by heavily shielded windows.
What is the unit of measurement used for heating of x-ray machines?
Heat Units
unit of potential x unit of tube current x unit of time
What are common causes of x-ray tube failure?
loss of vacuum
cathode filament failure
anode damage
bearing failure
