Nuclear Medicine Flashcards
What are the forces holding an atom together?
Strong nuclear force
Coulomb (electric force)
What is an Auger electron?
Another electron gets all the energy from an electron that drops down a level. This electron then flies off with all that excess energy.
What happens to excess energy from a nucleus relaxing?
A gamma-ray is released
Can create an Auger electron (which in turn causes a characteristic x-ray to occur)
How do Auger electrons cause x-rays?
An electron drops down a shell to fill the Auger electron’s place and a characteristic x-ray is released
What symbol represents ‘Mass Number’?
A
What symbol represents ‘Atomic Number’?
Z
What does ‘A’ represent in nuclear medicine?
Mass number (number of proton+ neutrons)
What does ‘Z’ represent in nuclear medicine?
Atomic number (number of protons/ electrons)
What symbol represents ‘Neutron Number’?
N
What does ‘N’ represent in nuclear medicine?
Neutron number
What are Isotopes?
atoms with the same atomic number but different mass number
What are Isobars?
atoms with the same mass number but different atomic numbers
What are Isotones?
atoms with the same number of neutrons
What is it called when nuclear decay transfers energy to an orbital electron rather than emitting a gamma ray?
internal conversion
What factors make a nucleus unstable?
large mass number (everything > 209 unstable)
number of protons/ neutrons very different
odd number of protons: neutrons
What are the generic names that atoms decay to/ from?
parent –> daughter
What is an alpha particle?
2 neutrons, 2 protons
What is a beta particle?
a free electron (or positron)
What is a neutrino?
a massless chargeless particle that travels at the speed of light and almost never interacts with matter
What is alpha decay?
when an alpha particle is emitted from the nucleus?
What is beta minus decay?
A neutron turns into a proton and releases an electron (and anti-neutrino)
What is beta minus decay also known as?
beta particle emission
What is beta particle emission also known as?
beta minus decay
What is beta plus decay also known as?
positron emission?
What is positron emission also known as?
beta plus decay
What is beta plus decay?
a proton turns into a neutron (and releases a positron)
What is required for positron emission to occur
a proton-rich nuclide with at least 1022keV of excess energy
What occurs after positron emission?
they interact almost immediately with a nearby electron and release two photons (511keV each)
What is ‘electron capture’ in nuclear medicine?
an inner-shell electron is drawn into a nucleus and combines with a proton to form a neutron and neutrino
What occurs after electron capture?
Electrons drop down to the inner shell and cause the release of either an auger electron or characteristic radiation
What is a metastable state?
an excited nucleus that may stay in the unstable state for a number of hours
What effects the rate of radioactive decay
only the number of unstable nuclei,
unaffected by temperature pressure etc
What are units of radioactive decay?
Becquerel (SI units)
- 1 disintegraiton/ second
Curie (historical/ USA units)
What is a decay series?
a series of radioactive reactions that occur, when one radioisotope decays into another that is also radioactive
What two types of particles can cause ionizing radiation?
charged particles
photons
What large charged particles can cause ionising radiation?
alpha particles
protons
deutrons
What are deuterons?
hydrogen particles with a neutron + proton
How far do large charged particles travel?
not very far
4cm in air, less in thicker tissue
What metric is used for how much radiation energy ionizing particles release as they travel?
linear energy transfer
What is pair production in nuclear medicine?
a photon splits into a positron and an electron
What conditions are necessary for pair production to occur?
the photon needs to have at least 1022keV of energy
What 3 processes make up photon attenuation in matter?
photo-electric effect
compton scatter
pair production
What is used to measure photon radiation in nuclear medicine?
scintillators
what is the most common scintillator in nuclear medicine?
Sodium Iodide (NaI)
What are desirable properties for scintillators
high Z
high light output
highly transparent
cheap
What are some issues with Na I scintillators?
low mechanical stability
absorbs water from air (hygroscopic)
What is used with scintillators to produce a measurable signal
a photomultiplier tube
What does a scintillator do?
absorbs ionising radiation and releases visible light
what does a photomultiplier tube do?
Converts light to electrons then amplifies massively
What occurs with the signal from a photomultiplier tube in nuclear medicine?
Cleaned up and then processed by a pulse height analyser (PHA)
What does a Pulse Height Analyser (PHA) do in nuclear medicine?
determines if the pulse is between a sweet lower/ upper boundary
