General Questions 2 Flashcards
What is the difference between excitation and ionisation?
Excitation is when an electron is moved to a higher energy level. Ionisation is when an electron is removed completely from the atom.
What energy is required to ionise a K shell electron in Tungsten?
At least 20,000 eV or 20 keV is required.
Define isobars, isotopes, isotones, and isomers.
Isobars: Nuclides with the same atomic mass. Isotopes: Nuclides with the same atomic number but different atomic mass. Isotones: Nuclides with the same number of neutrons. Isomers: Nuclides with the same atomic number and mass but different energy states.
Why is the energy released during de-excitation called a characteristic photon?
The energy difference between the electron levels is unique to the atom, making the photon characteristic of that atom.
What is the attenuation coefficient for a 50 keV beam when using a 7mm aluminum barrier?
The total attenuation coefficient is 0.1 mm^-1.
How does increasing beam energy affect the attenuation coefficient?
As beam energy increases, the attenuation coefficient decreases, meaning the probability of the beam passing through increases.
What are the purposes and units of tube voltage, tube current, and filament current?
Tube voltage (kVp): Accelerates electrons from the cathode to the anode. Tube current (mA): Controls the flow of electrons from the cathode to the anode. Filament current (A): Heats the filament to release electrons.
What is the difference between inherent and added filtration?
Inherent filtration: Filtration provided by the components of the x-ray tube. Added filtration: Additional materials attached to the tube for extra filtration.
How are photons produced via Bremsstrahlung and characteristic processes?
Bremsstrahlung: Occurs when electrons interact with the nucleus, releasing energy as photons. Characteristic: Occurs when a thermionic electron ejects a k-shell electron, and another electron drops to fill the vacancy, releasing energy as a photon.
What is the half-value layer, and what is lead equivalence?
Half-value layer: The thickness of material required to reduce beam intensity by half. Lead equivalence: The thickness of lead that provides the same protection as another material at a given energy.
What is voltage ripple, and how does it affect x-ray output?
Voltage ripple refers to fluctuations in the DC voltage across the tube. It affects the energy and quality of the x-ray beam by causing variations in photon energy.
What are somatic, genetic, stochastic, and deterministic effects of radiation?
Somatic: Appear in the individual exposed. Genetic: Appear in the offspring of the exposed individual. Stochastic: Probability increases with dose, but severity does not. Deterministic: Severity increases with dose above a threshold.
What are the three principles of radiation protection?
Justification: The benefit must outweigh the risk. Optimisation (ALARA): Keep doses as low as reasonably achievable. Limitation: Set dose limits for various groups.
Why do low-energy x-rays produce high contrast in images?
Lower energy x-rays lead to more photoelectric absorption, which is affected by the Z number. A small change in Z number results in a large change in attenuation, increasing contrast.
What causes an atom to become unstable?
An incorrect proton-to-neutron ratio within the nucleus causes instability.
