Radiopharmacy Flashcards
3 mechanisms to alter nucleus to make it unstable
- Cyclotron:
- Charged particle bombardment
- Nuclear Reactor
- Neutron activiation
- fission products
Describe how a cyclotron works
- Pair of hollow semi-circular electrodes (DEES) with gap
- In magnetic field perp to charged particle movement plane
- charged particle introduced into centre accelerated towards dee by voltage
- No E-Field inside the D, only accelerated across the gap
- Electrons follwo curved path due to magnetic field
- Alternating voltage used to accelerate towards other dee,
- repeat, outward spiral
- Electrons hit target with high energy
Cyclotron Products:
What have we added, how do they decay?
examples and use?
Added protons, so the products are proton rich, and decay via electron capture of positron emission
Changes the atomic number, so now it’s a different element and can be separated chemically from the target
e. g. F-18 for FDG PET
e. g. I-123 for DaTSCAN (brains)
Describe fission in Nuclear Reactor
- U-235 undergoes fission -
- neutron hits nucleus and splits it into smaller fragments (daughter nuclei) and releases 2-3 high energy free neutrons
- 235U + n -> 236U
- High energy neutrons go on to make more interactions
- 236U nucleus is highly unstable and fissions into two smaller fragments producing wide range of mass numvbers >200 radionucleuides
- Products are neutron rich, and decau via beta necay
Name and describe 3 main components of nuclear reactor core
What do you have to do to the neutrons to make them more likely to be fissile?
- Uranium fuel rods - the source of the reaction
- Control Rods - steel enriched with boron, absorb neutrons to reduce number of neutrons available to cause fission
- Moderator - water or graphite, slows neutrons down and makes them more likely to cause further fission.
Nuclear fission produces RNs from which 2 processes?
give examples
how can you separate them?
- Fission fragments - produced directly in reaction and extracted chemically, e.g. Mo-99
- Neutron activation - large flux of neutrons used to bombard other targets, e.g. P-32. Here you have added neutrons, so can’t be separated chemically.
RN generator
Why do we need them?
Need them to turn long-lived parent RNs into short-lived RNs for diagnostic tests that would otherwise decay away in transport
RN generator
What is generator transient equilibrium?
What do the graphs look like?
Parent is constantly decaying, daughter is produced and then also decays. Rates are linked. At equilibrium, the rate of formation = rate of decay, and after that the ratio of activity from parent and daughter is constant.
What actually happens is that we elute the generator and remove the daughter so you get this build up to the parent from 0.
How do you get the Tc-99m out of the generator?
- Elute by washing with saline
- MoO42- is adsorbed onto aluminium oxide collumn
- Decays to Pertechnetate (TcO4-) – single charge so less tightly bound
- Pulling saline through chlorine ions replace the TcO4- ions.
- Eluate contains Na+ TcO4-
- Tubing allows the collumn to be washed
- Filter keeps Aluminium Oxide within column, also removes small particles
- Lead shielding for operator safety from gammas
Radionucleide Calibrator RNC
Purpose?
Operating pinciples
RNC measures radioactivity MBq and GBq range
- Chamber has pressurised gas, plates at high voltage
- Radiation causes ionisation in gas, measure current as ions ar pulled to outer walls
- Current porportional to activity (depends on energy of radiation) hence you need calibration factors. RNCs cannot differentiate between energy of RNCs, need operator to choose the right dial setting (pE/MBq)
Radionucleide Calibrator RNC
What does the current depend on (x6)?
–Activity of the radiation source
–Energy of the radiation
–Source container/geometry – vial/syringe etc
–Measurement position
–Composition & Pressure of gas
–Applied Voltage
Describe the 5 points on the voltage response curve
Which does th RNC operate in?
- Recombinations
- Ion saturation
- Proportional
- Limited proportional
- Geiger-Muller
RNC operates in ion saturation region, this is because you do not want the current to be dependent on the voltage that you apply.
RNC QC
Daily and Annual
Daily: test with long-lived source (Cs137) and check the response against the baseline values for caibration
Annual - accuracy & linearity, comapring to NPL via reference instrument. Asking is the measured response proprtional to the known tru activity over the entire activity range that it is used?
Can you measure pure beta emitters in a radionuclide calibrator? E.g Y-90
Yes, you can measure the bremsstrahlung produced from the wall of the vialsyringe, chamber wall, and within source.
But it heavily depends on the container and the volume of the source
Can you measure I-123 with RNC?
2 ways to fo it?
I-123 decasys via EC and emits 159kev gamma-rays and 28kev characteristic x-rays. Ion chamber is very sensitive to low energy x-raysAgain depends heavily on container anad volume
- Method 1: work out correction vactors for different vials and syringes and volumes, hard to do.
- Method 2: use copper filter (0.5mm), removes low energy x-rays and only attenuates 159kEv gammas by 14%. Need new CF to account for Cu filter.
