Learning points from Oxford book MCQs Flashcards
Do stable nuclei contain equal numbers of protons and neutrons?
No
Higher number of neutrons needed for stability at higher atomic numbers
What is the valence shell?
The outer shell of an atom with electrons in
When does ionising radiation follow the inverse square law?
if it is from a point source and unattenuated
How can secondary electrons ionize atoms?
by interacting with outer shell electrons
Can ionizing radiation cause direct damage to tissue?
Yes
What is internal conversion?
atomic decay process where an excited nucleus interacts electromagnetically with one of the orbital electrons of an atom. This causes the electron to be emitted (ejected) from the atom.
This can then also lead to characteristic xray production as the K-shell electron is filled
What happens in positron emission?
proton -> neutron + Beta+ emission. therefore atomic number falls by 1
How is radioactive decay measured?
disintegrations per second
One becquerel is defined as an activity of one per second
Is the speed of decay effected by physical conditions?
Decay rate is not affected by physical conditions
Are radionuclides with shorter or longer half lives safer to store?
Shorter time to decay to negligible activity is safer
Why is efficiency of xray production higher with rotating anode?
better heat distribution means different factors can be used
does cathode-anode distance effect radiation output?
No
Does anode angle effect FOV?
Yes The steeper the angle, the narrower the ‘useful’ x-ray beam and the smaller field covered.
Should the cathode filament have high or low vapour pressure?
It should have a low vapour pressure as this means it is less likely to evaporate
How does increased kV effect ESD?
increases it if all other factors are kept equal
in a question without this statement though assume mA would go down and actually ESD will go down.
How does increased kV effect scatter?
Higher kV -> increased scatter at the film
What is the difference between total attenuation and attenuation coefficient?
Total attenuation is the product of Compton, photoelectric, and elastic attenuation effects. . Attenuation coefficient is the sum of each process.
Is the HVL for Lead of Aluminium greater?
HVL for aluminium is bigger than that for lead as you need more material to attenuate to half.
HVL goes down with increasing Z.
What is MAC measured in?
cm^2/g
Is LAC or MAC more clinically relevant?
The linear attenuation coefficient has more practical applications, as film density produced by a certain depth of tissue is more useful than that produced by a certain mass of tissue.
What electrons do Compton interactions occur with?
Free or outer shell electrons
What energies in soft tissue and bone does the Compton effect overtake photoelectric effect?
Bone @ >50
ST @ >30
Is there scatter associated with the photoelectric effect?
No as the incident photon is completely absorbed
T or F - The kinetic energy of electrons (keV) interacting with the target is equal to the kV
between the anode and cathode of the X-ray tube
T
