Uses (in general)
- The choice of a R.isotope depends on its half life and the type of radiation it emmits.
- In rarer cases the choice also depends on how its obtained and whether or not it produces a stable decay product.
- For medical uses of R.isotopes, the toxicity and biochemical stability is also an important factor.
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- Living plants (etc) contain a small % of the R.isotope C-14; formed in the atmosphere by cosmic rays knocking neutrons from nuclei, which then collide with nitrogen nuclei to form 6C-14.
- The trees/plants then take in Carbon Dioxide as part of photosynthesis thus a small % of the carbon content is C-14. C-14 has a half life of 5570 years so has negligible decay during the plants lifetime. Once it dies though; no more C-14 is taken in so the proportion of C-14 starts to decrease as the nuclei decays.
- The activity is proportional tp the No. of atoms yet to decay, so measuring the activity of the dead ample enables its age to be calculated as long as the activity of a live sample is known.
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- Ancient rocks contain trapped argon gas from the decay of a R.isotope of pottasium-40 into an argon-40 isotope. This occurs when the pottasium nucleus captures an inner shell electron, and as a result, a proton in the nucleus changes into a neutron & a neutrino is emmited.
- The potassium isotope also decays by beta minus decay to form a calcium isotope. This process is 8x more likely than the electron capture.
- The effective half life of pottasium-40 is 125,000,000 years.
- The age of the rock (when solidified) is calculated by measuring the proportion of Argon-40 to Pottasium-40.
- For every N Pottasium-40 atoms, there's 1 Argon-40 atom & there must of have originally been N+9 potassium atoms (Because 8 are now calcium!)
- Radioactive decay equation: N=N0e (etc...) can be used to find the age of the sample.
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A R.tracer is used to follow the path os a substance through a system.
Generally the R.isotope in a tracer should:
- Have a half life stable enough for necessary measurements to be made, but short enough to decay quickly after use.
- Emmit Beta or Gamma radiation so it can be detected outside of the system.
*****!!!See table for specific Tracers!!!*****
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- Engine wear: The rate of wear of a piston ring in an engine can be measured by fitting a radioactive ring. As the ring slides along the piston compartment, R.atoms transfer to the engine oil. By measuring the radioactivity of the oil, the R.mass can be determined and thus the rate of wear can be calculated. (The metal ring is made radioactive by exposing it to neutron radiation in a reactor. Each nucleus that absorbs a neutron becomes unstable and decays by beta minus.
- Thickness Monitoring: Metal foil is manufactured by using rollers to compress plate metal on a continous production line. A detector measures the amount of B minus radiation passing through the metal. If it's too thick, the reading drops, and the detector relays a signal to the control system to make the rollers move closer together. (The source used has a long half life!)
- Power sources for remote devices: Satalites, weather sensors (etc) can be powered using a radioactive isotope in a thermally-insulated, sealed container that absorbes all of the radiation emmited. A thermocouple attatched to the container produces electricity as a result of the container becoming warm. Because each disintegration of a nucleus release energy, the e transfer per second (from the source)=LamdaNE. Source needs to have relitively long half life so it doesn't need to be replaced too often, but a very long half life may require too much mass to generate the necessary power.
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