radionuclide production Flashcards
production of radionuclides
direct:
nuclear reactor (neutron rich isotopes)
cyclotron (accelerator) (neutron deficient)
indirect:
generator
nuclear reactor
(neutron rich isotopes)
large quantities low cost
- fission of uranium-235 and its subsequent fragments
- bombardment of stable targets
fission
neutron slams into a larger atom, forcing it to excite and split into two smaller atoms. Additional neutrons are also released that can initiate a chain reaction.
the products have an excess of neutrons
so can undergo beta minus decay
they have high specific activity
undesirable decay modes
lack if specificity
separation challenging
specific activity
the ratio of radionuclide activity to the total mass of the element present
MBq/g
high specific activity = carrier-free
carrier = non-radioactive element
bombardment
place stable nuclide target in reactor
irradiation by neutron flux creates a mixture of stable target material and radioactive product
(for radionuclides that cant be produced through fission)
eg Mo-98 to Mo-99
low specific activity
products are:
neutron rich
decay by beta
have long half lives
cyclotron
2 evacuated hollow D-shaped electrodes with gap between
oscillating polarity accelerates charged particles
releases +ve and -ve ions in bursts
magnets to help circular direction of travel
isotopically enriched material as target
requires cooling
products:
neutron deficient isotopes
high specific activity
short half lives
decay by beta and electron capture
cyclotron production ions
positive
inefficient
up to 30% beam lost
activating
negative
almost 100% efficient
non-activating (cold)
generator
can provide steady local supply of useful short lived radionuclides
long lived parent decays to shorter half life daughter
parent and daughter needs to be separated
periodic delivery of generator
decay by isomeric transition, emits mono-energetic gammas
decay by EC, and beta plus, emits positrons
molybdenum-99/technetium-99m generator
elution = removal of technetium by passage of saline
eluate(output) vial at low pressure
reservoir contains saline for higher pressure
pressure diff draws saline into column
column contains Mo99
saline washes off tc-99m into eluate
after elution, tc-99m activity builds up again
chance of Mo-99 in eluate,
check by measuring eluate activity
technetium-99 benefits
cheap
pure gamma emitter
readily available
non toxic
carrier free
high specific activity
technetium generator
tc-99m gives 2 energy gamma photons
decays to tc 99
transient equilibrium
daughter has shorter half life
amount of daughter product runs parallel to the amount of parent activity after a build up of time
approx 4xdaughter half life
tracer principle
radioactive compounds participate in physiological process the same as non-radioactive compounds
by using a trace amount of radiolabelled pharmaceutical, the radiopharmaceutical observes/= or treats the targeted physiological process without changing this process
good sensitivity
non-invasive
iodine-123
cyclotron
decays by electron capture
13 hours half life
iodine 131
fission
8 days half life
