40 Questions
What is the shape of an s-type electron orbital?
Spherical
What is the typical arrangement of lobes in a d-type electron orbital?
Four lobes
Which type of orbital is filled first in every element?
s-type
What is a characteristic of p-type electron orbitals?
They are bilobed
What happens to electron clouds in an atom with many electrons?
They are superimposed with the electron clouds of other orbitals
What is the maximum number of orbitals known in an atom?
Seven
How do electrons occupy orbitals?
They occupy the lowest energy available orbitals
What is unique about the fifth d-type orbital?
It is bilobed with an encircling ring
What is the result of a smaller effective focal spot?
Increased sharpness of the image
What is the purpose of the beveled disk in a rotating anode?
To distribute the heat over a larger area
What is the difference between a stationary anode and a rotating anode?
The presence of moving parts
What is the advantage of using a rotating anode over a stationary anode?
Increased heat dissipation
What is the shape of the focal spot in a rotating anode machine?
Focal track
What is the maximum tube current possible with a rotating anode?
10-50 times that of a stationary anode
What is the purpose of the kVp selector?
To set the X-ray energy
What is the result of the electron beam striking successive areas of the target?
Widening of the focal spot
What is formed when an incident electron ejects an electron from an inner orbital?
A photoelectron, a recoil electron, and an electron vacancy
What happens to the electron vacancy created in an inner orbital?
It is filled by an electron from an outer orbital
What determines the energy of the photon emitted when an electron fills an electron vacancy?
The difference in energy levels between the two orbitals
What is the characteristic of the photons released in the process?
They are characteristic of the target atom
What causes the electrons striking the target to have varying levels of kinetic energy?
The continuously varying voltage difference between the target and filament
What happens to the electrons as they pass around the tungsten nuclei?
They are deflected to varying extents
What is the result of the electrons being deflected by the tungsten nuclei?
They lose kinetic energy and emit bremsstrahlung photons
What happens to most electrons in the target?
They participate in multiple bremsstrahlung interactions before losing all their kinetic energy
What is the primary function of a filter in an x-ray beam?
To remove low-energy photons
What are the three controls typically found on many x-ray machines?
Exposure time, tube current, and tube voltage
What happens to the x-ray beam when it encounters inherent filtration?
The beam is attenuated
Why is it recommended to operate the machine at the highest mA value available?
To minimize patient movement
What is the purpose of the barrier material in the x-ray tube?
To prevent oil from escaping
What is the effect of using the highest tube voltage available?
It produces a higher-energy beam
What is the role of the glass wall of the x-ray tube in inherent filtration?
It absorbs low-energy photons
What is the recommended approach when the tube current can be adjusted?
To use the highest mA value available
What is the primary function of collimators in x-ray imaging?
To improve image quality by reducing scattered radiation
What happens to the x-ray beam as it passes through the patient?
It is reduced in intensity due to absorption and scattering
What is the effect of changing from a short aiming tube to a long aiming tube?
A decrease in skin exposure
What is the result of Compton scattering in the patient's tissues?
The scattering of photons in all directions
What is the purpose of adjusting the kVp or mA after changing the aiming tube?
To maintain a constant skin exposure
What is the effect of collimating the x-ray beam?
A reduction in scattered radiation
What happens to the x-ray beam as it interacts with the patient's tissues?
It is partially absorbed and scattered
What is the characteristic of the x-ray beam in dental imaging?
It is spatially homogeneous
Study Notes
Electron Orbitals
- s-type electron orbitals are spherical and centered around the nucleus.
- p-type electron orbitals are bilobed and centered around the nucleus.
- Four of the five d-type electron orbitals are made up of four lobes, centered on the nucleus.
- The fifth d-type orbital is bilobed with an encircling ring.
Electron Orbital Filling
- s-type orbitals are the first to be filled in every element.
- p-type orbitals are filled next, followed by d-type orbitals.
- Electrons occupy the lowest energy available orbitals, not already occupied by other electrons.
X-ray Tubes
- A stationary anode is used in some x-ray tubes, which has no moving parts.
- The focal spot of a stationary tube is a small area, resulting in heat concentration.
- Rotating anode tubes have a beveled disk that rotates when the tube is in operation, widening the focal spot and distributing heat over a larger area.
- Rotating anode tubes can be used with higher tube currents (100-500 mA), compared to stationary targets (10-50 times less).
X-ray Generation
- Incident electrons eject electrons from inner orbitals, creating photoelectrons, recoil electrons, and electron vacancies.
- Electrons from outer orbitals fill the vacancies, emitting photons with energy equal to the difference in energy levels between the two orbitals.
- The continuously varying voltage difference between the target and filament causes electrons to have varying levels of kinetic energy.
- Bombarding electrons are deflected to varying extents, giving up varying amounts of energy in the form of bremsstrahlung photons.
X-ray Controls
- Exposure time, tube current (mA), and tube voltage are the three controls found on many x-ray machines.
- It is recommended to use the highest mA value available and operate the machine at this setting for the shortest exposure time and minimal patient movement.
X-ray Interactions
- About 90% of photons are absorbed by hard and soft tissues, and about 10% pass through the patient.
- Absorbed photons generate scattered radiation within the exposed tissues by Compton scattering.
- Collimators improve image quality by reducing the exposed volume and the number of scattered photons reaching the film.
- Changing the distance between the x-ray tube and the patient requires a corresponding modification of the kVp or mA to keep constant the exposure to the film or digital sensor.
Learn about the different types of electron orbitals, including s-type, p-type, and d-type orbitals, and how they are filled in elements.
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