Radiation Physics 1 Flashcards
Shells in an atom are numbered from?
1 to 7
If the shells are labeled with letters, they are?
K to Q
The previously mentioned number of letter is known as the shell’s?
Principal quantum number or n
What is the formula for the number of electrons a shell can hold?
2n^2
How do you calculate atomic mass?
of protons + # of neutrons
What causes particulate radiation? What is the capacity to ionize based on?
Moving particles. Mass, velocity, and charge affect the capacity to ionize
What is an alpha particle and how ionizing is it?
Helium atom with no electrons. Very ionizing so it doesn’t travel very far
He 2+
What is a beta particle and how ionizing is it?
An electron that has been emitted from a radioactive nucleus. It is not very ionizing and thus travels further
What is linear energy transfer
Loss of energy as a particle moves through tissue
What factors can increase linear energy transfer?
Increasing size and charge and decreasing velocity
Other than particulate radiation, the other kind is?
Electromagnetic radiation
The x ray machine consists of what 3 parts?
Power supply, control panel, tube head
What is used to absorb heat created by the x ray tube?
Mineral oil
The filament in the cathode is the source of? What is it made out of?
Electrons, made of a coiled piece of tungsten
What is the focusing cup of the cathode?
Negatively charged concave reflector that repels electrons.
What is the focusing cup made of?
Nickel or molybdenum
The anode is made of?
Tungsten target embedded in a copper stem
What does the anode do and how efficient is the process?
Convertes the kinetic energy from the phi lament into photon energy or x-rays. Highly inefficient, 99% lost as heat
What 4 properties of tungsten make it the best choice?
High atomic number and efficient in making x-rays
Highest melting point of any metal so it can withstand the heat generated
High thermal conductivity and it dissipates heat into the copper stem
Low vapor pressure which helps maintain the vacuum
What type of anode is better for a dental setting, rotating or stationary?
Stationary
What is the focal spot? How does focal spot size affect radiographic image sharpness?
The focal spot is where the focusing cup directs electrons from the filament. Sharpness of the image increases as focal spot size decreases
What determines the intensity of the x-ray beam?
Tube current or mA and tube voltage or kVp
What determines the number of electrons and x-rays produced?
The tube current or mA, higher mA= more electrons
What are the two processes that produce x-rays?
Bremsstrahlung and characteristic radiation
What produces bremsstrahlung?
Sudden stopping or slowing of the electron at the target
Which produces the majority of x-ray photons?
Bremsstrahlung
What is exposure?
How many x-ray photons are produced
What is the combined unit for current and exposure time?
milliamp seconds
Older x-rays used what unit for time?
An impulse which was 1/60th of a second
Half wave rectification is AKA? How does it work?
Self-rectification, limits machine to using half the AC cycle
Most dental x-rays now use?
DC cycle because it provides more uniform energy
What is tube rating?
Maximum exposure time an x-ray may be energized for single exposure or max time you can leave the tube on before it gets too hot
What is duty cycle?
Frequency at which exposures can be made
When characteristic radiation occur?
When a high speed electron from the filament displaces an electron from the inner shell of the tungsten atom. An outer shell electron drops in and emits a photon
What affect does the focal spot have on heat?
Heat increases as the size of the focal spot decreases
What is external filtration and what is used?
Removing low energy photons from the beam using an aluminum filter
What is the half value layer?
The thickness needed to absorb half of the beams energy
What is inherent filtration?
Absorption from anything that is not the aluminum filter
How much aluminum equivalent is needed up to 70 kVp and over?
1.5mm under and 2.5mm over
What does collimation do?
Limits beam size and patient radiation exposure
What shape collimator do we use for intraoral exposures?
Rectangular
How does a collimator increase image quality?
By reducing scatter radiation
