Radioisotopes Flashcards
What is an atom composed of?
Protons: element
Neutrons: isotope
electrons
As the atomic number of an atom increases, what’s needed in order to stabilise it?
more neutrons are needed to stabilise it
What are the types of emitters that contribute to nuclei decay and what causes these emitters to be released?
Beta- emitters: too many neutrons
Beta+ emitters: too many protons
Alpah emitters: isotope too heavy and needs to loose mass
Gamma emitters: nuclei excited
What are alpha emitters and give an example of one?
Tell me the key features of alpha emitters?
- alpha particle
- He2+
- occurs in heavy element such as 238U and 210P
- Highly ionising
- Low penetrating power (due to its mass): few cm of air/ outer layer of skin
- Energy ≈ 5 MeV (mega electron volts)
210Po –> 206Pb + He2+
Tell me about beta emitters and their key features and an example of a beta emitter?
- beta particle
High enegry electrons emitted from nucleus
Accompaned by emission of anti-neutrino
- occurs in nuclei with too many neutrons
mass remains the same
element changes (atomic number increases by +1)
- medium penetrating power
- energy: varies, typically < 3 meV
- e.g. Carbond -14
14C –> 14N + 0e + 0V
Tell me about gamma emitters and their key features?
- Gamma radiation with high frequency photons
- occur in nuclei in excited state
frequenctly follow alpha or beta decay
- high penetrating power
Lead shiled wont completely stop
- Energy varies: 10’s to 1000’s KeV (kiloelectron volts)
- no change in isotope number of mass
When will nuclei stop decaying?
When a stable isotope is formed
The rate of decay is proportional to concentration of material. What equation described this?
Write the rate of decay equation is respect to Kt ?
What is the half life equation?
What equation did the half life equation (t1/2) come from?
How can we determine the rate of decay?
by counting the number of decays per secnd (dps)
what’s the relationship between
Bq (Becquerel) and dps?
1 Bq = 1dps
What does 1 Ci (curie) equal in dps?
1 Ci = 3.7x1010 dps
What can be used to measure radioactivity?
- ionising detector
- scintillation detector
How does an ionising detector work?
- ionising radiation interacts with inert gas
- which causes the release of an electron and ion
- these migrate to an electrode and generate a current
What are the pros and cons to a ionising detector?
Pros
- Can detect most types of radiation
- cascade can amplify signal (Gieger muller tube)
Cons
- not easy to apply to liquid samples
How does a liquid scintillation counter work?
- samples to be counted are prepared by adding scintillation fluid (cocktail) to the beta emitter
- as beta particles are released and interact with the fluid, photons of light are produced and measured
- the intensity of light is proportional to the energy of the beta particle; therefore the spectra for different energy beta emitters are unique
What the effects of particle energy on scintillation detection?
- the size of response is proportional to the energy of particle
- enable simultaneous detection of different isotopes
Whats the equation for the counting efficiency?
Counting efficiency= CPM / DPM
CPM= counts per minute
DPM= decays per minute
Whats the equation for DPM?
DPM = CPM / counting efficiency
What effects counting efficiency?
Name and explain the different types of this?
Quenching
1. Chemical quenching
- agents in cocktail interfere with transfer from solvent to fluorophore
2. Colour quenching
- agents in cocktail absorb light in region in which fluorophore emits
3. Self-absorption
- particle does not enter cocktail- particular acute for weak beta-emitter (3H)
What are the uses of measuring radioacitivity in biology?
- Tracers in metabolic pathways
- imaging
- binding/ transport assay
Tell me about imaging (scintigraphy. single-photo emission computerised tomography)
- gamma emitting radio-nucleotides ingested
- emission detected using solid-state gamma cameras
- 3D image can be built up by rotating detector around the patient
