Production of X-rays part 2 Flashcards
The higher the kVp the _______ the chances of having x-rays
higher
What is electricity?
Flow of electrons through an electrical conductor
What is current?
Amount of electrons flowing through a conductor per second. Measured in amperes (A).
- mA
What is circuit?
Path of electrical current
What is voltage (potential difference)?
Difference in electrical potential energy between two points in an electric circuit. Measured in volts (V).
What do you need to turn a current from alternate to direct?
rectifier
What type of current can pass through a transformer?
alternate current
What type of current CANNOT pass through a transformer?
direct current
During each half-cycle (1/120 of a second), anode is _______ and attracts the electrons from the cathode (x-radiation ____ produced).
positive
is
During each alternate half-cycle (1/120 of a second), anode is ________, therefore, no attraction for electrons exists and x-radiation ____ produced.
negative
is not
How many cycles of current happen per second in the USA?
60 cycles per second
How many cycles of current per second do you need to make x-rays?
110 cycles per second
If only alternate current was used in an x-ray machine what would happen?
electricity would go back and forth from anode to cathode and vice versa (x-rays only produced half of the time)
What does a full wave rectifier do?
Only goes in one direction from max to zero and back again
How do you go from alternating current from the wall to a direct current with a high mean energy?
- Changing alternating current into direct current
- Full-waive rectification, high frequency power supply
- Essentially constant potential between cathode and anode.
- Higher mean energy of beam compared to AC.
What does a constant potential and direct current lead to in terms of…
exposure time
beam intensity
mean energy of beam
radiation dose
- Shorter exposure times
- More consistent beam intensity
- Higher mean energy of beam
- Decreased radiation dose
How are x-rays produced?
X-rays are produced whenever high-speed electrons are suddenly decelerated or brought to a stop when they pass close to the nuclei of a high Z # absorbing material (in this case tungsten 74W)
What are the two mechnanisms for x-ray formation?
- Bremsstrahlung radiation
- Characteristic radiation
What is another term for breaking radiation?
Bremsstrahlung radiation
What type of x-ray formation is electron to nucleus interaction?
Bremsstrahlung radiation
What type of x-ray formation is electron to electron interaction?
Characteristic radiation
What happens during Characteristic radiation?
◦ A few electrons interact with tungsten target orbital electrons, imparting enough energy to ionize the tungsten target.
◦ When electrons displace inner shell electrons, characteristic radiation is produced
What happens during Bremsstrahlung radiation?
◦ The fast-moving electrons either slow down or stop when they come close to the nucleus of the atoms and part of their energy is transferred as X-rays.
Bremsstrahlung radiation increases
with increasing what two components?
- the voltage (kV)
- the atomic number of the target (Z#)
The higher the velocity,
the _______ the KE of electrons
greater
What type of energy is lost when an impinging electron is deflected and decelerated than this energy is emitted as an x-ray photon?
kinetic energy
What allows for the maximum energy photon from Bremsstrahlung radiation?
Head-on collision with nucleus
What gets rid of the low energy x-rays?
aluminum filter
Which type of x radiation has a wide distribution of wavelengths (heterogeneous)?
Bremsstrahlung radiation
What is the reason that Bremsstrahlung radiation is heterogeneous (multiptle wavelengths)?
◦ Electrons lose their energies in random fashion when they interact with tungsten atoms.
◦ Multiple interactions between electrons and tungsten atoms.
What happens to the electrons in Bremsstrahlung radiation?
At the anode they either interact with the nucleus or rapidly decelerate and get deflected (change of direction).
How does characteristic radiation occur?
- Arises when cathode electron collides with inner orbital electron of tungsten atom (target) and removes it from orbit.
- Atom is now ionized and unstable.
- Immediately, the hole left by the electron is filled by an electron from an outer shell, and energy is emitted from this electron in the form of x-radiation characteristic of tungsten and the involved shell
The energy emitted in characteristic radiation by the electron is equivalent to…
the difference in the binding energies of the two shells/orbitals
What is the characteristic radiation ev for L to K transition?
57,400 ev
What is the characteristic radiation ev for M to K transition?
66,700 ev
___% of diagnostic x-ray beam is characteristic radiation
30%
_____________ radiation makes up the majority of the x-ray beam and produces a heterogeneous beam of varying photon energies
Bremsstrahlung
____________ radiation is only a minor source of radiation from the x-ray tube and produces photon energies specific for the target material
Characteristic
