Production of X-rays Flashcards
What is the atomic number?
number of protons
what determines identity of atom
What is the atomic mass?
protons + neutrons
What is the binding energy?
minimal amount of energy required to remove an electron from its shell
Which shell is the most tightly bound?
K
How much energy does it take to remove a K shell electron in Tungsten?
70,000 eV // 70 keV
How is electron binding energy related to atomic number?
proportionally: higher atomic number = more protons –> higher atomic binding energy
What describes creating a positive & negative ion by removal of an electron from a neutral atom?
ionization
What is the transmission of energy through space in a vacuum & matter?
radiation
What are the two forms of radiation?
wave & quantum
Describe properties of the wave theory.
explains propagation of radiation
radiation in form of waves
no mass
speed of light
Describe properties of quantum theory.
explains the interaction of radiation with matter
considers radiation small bundles of energy called photons: mass & travel in straight/diverging lines at speed of light
What is high energy radiation?
high frequency & short wavelength
What is low energy radiation?
low frequency & long wavelength
How are frequency & wavelength related in wave theory?
inversely proportional
Where does the electromagnetic spectrum become ionizing?
blue light (ultraviolet spectrum)
List the electromagnetic spectrum from lowest energy to highest.
radio, micro, infrared, visible, ultraviolet, x-ray, gamma
In the quantum theory of radiation are the particles charged?
they can be, but neutrons & x-rays are not
What is the heaviest & most charged particle of radiation?
alpha
What is the linear energy transfer (LET)?
ionizing rate: low LET for x-rays allows particles to move through tissue easily to reach receptor
How is contrast created when considering the particle theory?
some energy/x-rays remain in tissue…cannot penetrate & remain trapped
What particle has the highest LET and why?
alpha: electrical charge & weight
What are the factors that lead to higher LET?
low velocity, higher charge, bigger size –> less penetration because lose energy over short distances
US law states that x-ray machines must have what features?
dead-man type exposure button
indicator light
audible sound
What is located inside the tube head?
power supply & x-ray tube
Where is the step up transformer?
anode end
Where is the step down transformer?
cathode end
What charge are the cathode & anodes?
cathode = negative
anode = positive
Where are the electrons produced?
cathode
What is the purpose of the aluminum filter?
filters non-useful x-rays so only the ones that will create an image exit the tube head
What is in the cathode?
focusing cup (Mb) negatively charged
filament (tungsten)
Where is the source of electrons?
filament
How are electrons produced?
thermionic emission
How do we make the filament hotter to create more electrons?
increase the voltage/energy
Which transformer heats up the filament?
low energy / step-down
What is at the anode end?
tungsten target & copper stem
How efficient is the tungsten target at transferring kinetic energy of the e- into x-rays?
highly inefficient: only 1% become x-rays
What is the purpose of the copper stem?
works as a thermal conductor to remove heat & prevent target from melting
Where is the source of x-rays?
focal spot
What happens if the target melts?
vapors/materials enter the x-ray tube & it is no longer a vacuum
Why is a vacuum needed?
we do not want x-rays to interact with anything & want the full energy of them to create our radiographs
Why is tungsten a good target material?
high atomic number
high melting point
high thermal conductivity
low vapor pressure
The low voltage current heats up the _____ resulting in ______.
tungsten filament
separation of outer shell e- from atom
How many volts does the low-voltage/step-down transformer produce?
6-12 volts
How many volts are required to remove a k shell electron of tungsten?
70kp
How is the focal spot related to spatial resolution?
smaller focal spot = higher resolution
How do we avoid heat accumulation on the focal spot?
line-focus principle
How does the line-principle work?
angling of target creates smaller effective focal spot compared to actual focal spot…results in sharper resolution, while maintaining original surface area of target for heat dissipation
The step down transformer is regulated by what switch?
mA
Increasing mA setting will increase what?
number of electrons emitted
The step UP transformer is regulated by what switch?
kV setting
Increasing kV will increase the ?
energy of the electrons traveling from the cathode to the anode
If you increase the exposure time, how does that effect the amount of xrays produced?
increases…proportional
What term means flow of electrons through an electrical conductor?
electricity
What term means the amount of electrons flowing through a conductor per second?
current
what is current measured in?
mA
What is the path of electrical current?
circuit
What is the difference in electrical potential energy between 2 points in an electrical circuit?
voltage (potential difference)
What is voltage measured in?
kVp
In the USA how many cycles per second?
60
T/F During each cycle there is a phase where the anode is positive & attracts e- and a phase where the anode is negative & repels e-?
true
T/F the current is constant?
false
During what part of the cycle are x-rays produced?
when the anode is positive & attracts e-
Why does the current have to be alternating?
because direct current cannot pass through the transformer
Why do we need direct current?
once we pass through the transformer we want direct current to ensure that the flow of e- is in one direction towards the anode
What device converts the current from alternating to direct?
rectifier
How do we create a nearly constant potential?
give multiple pulses after rectification so that the amount of energy/volts stays nearly constant between cathode & anode
Why do we want the higher voltage to be constant?
more efficient at producing x-rays & the x-rays will have higher energy
Constant potential & direct current means that we can have…?
- shorter exposure times
- more consistent beam of intensity
- higher mean energy of beam
- decreased radiation dose
How are x-rays actually produced ?
when the high-speed e- suddenly stop/decelerate close to the nuclei of a high Z # absorbing material (tungsten)
What are the 2 mechanisms for x-ray formation?
- Bremsstrahlung
- Characteristic
Which mechanism describes an e- to nucleus interaction?
Bremsstrahlung
Which mechanism describes an e- to e- interaction?
characteristic
Describe the spectrum of x-ray energy for Bremsstrahlung radiation?
all the way to max if head on collision occurs (wide distribution/heterogenous)
Describe the type of energy emitted by an e- in characteristic radiation?
energy is equivalent to the difference in binding energies of the 2 shells/orbitals
Majority of x-ray beams are produced in which way?
Bremsstrahlung radiation
