Radioactivity Flashcards
Carbon dating
Living plants contain a small percentage of radioactive C-14
Negligible decay throughout the lifetime of the plant - half life of 5570 years
Once dead no further carbon is taken in so the proportion of C-14 begins to fall
Calculate age of sample using n = Ne^-lambda x t
Argon dating
Ancient rocks contain trapped argon gas as a result of the decay of K-40 to Ar-40
Half life of K-40 is 1250 million
Age can be calculated by measuring the proportion of Ar-40 to K-40
For every N K-40 atoms if there is 1 Ar-40 then there must of been N+9 K-40 atoms originally
Radioactive tracer requirements
Should have a half life long enough for necessary measurements to be taken but short enough to reduce damage caused
Emit beta or gamma radiation so the radiation is able to be detected outside
Engine wear -> piston ring
Rate of wear of a piston ring can be measured by fitting a radioactive ring
Radioactive atoms transfer from the ring to the oil
By measuring the radioactivity of the oil the mass transferred from the ring can be determined and the rate of wear calculated
Detecting underground pipe leaks
Beta or gamma emitter injected injected into the flow (depending on depth, soil density etc)
A detector on the surface above the pipeline is used to detect leakage
Modelling oil reservoirs mathematically to improve oil recovery
Water containing a tracer is injected into an oil reservoir at higher pressure, forcing some of the oil out
Detection at the production wells monitor the presence of the radioactive isotope to see how much oil is being lost
The tracer is tritaited water, a beta emitter with a half life of 12 years
Investigating the uptake of fertilisers by plants
Plant watered with a solution containing a fertiliser which contains P-32, a beta emitter with a half life of 14 days
By measuring the radioactivity of the leaves, the amount of fertiliser reaching them can be determined
Monitoring the uptake of iodine by the thyroid gland
Patient is given a solution containing sodium iodide which contains a small quantity of radioactive I-133 (beta emitter with a half-life of 8 days)
The activity of the patient’s thyroid and the activity of an identical smaller prepared at the same time is measured 24 hours later
Thickness monitoring
Detector measures the amount of radiation passing through the foil
If the foil is too thick, the detector reading drops and the rollers move closer together to make the foil thinner
and vice versa
The source is a beta emitter with a long half-life
Power sources for remote devices
Satellites, weather sensors etc
Radioactive isotope in a sealed container which absorbs all the radiation emitted by the isotope
Thermocouple attached to container produces electricity through the heat from the absorption of the radiation
Reasons for nuclear instability
Too many neutrons
Too few neutrons
Too many nucleons - too heavy
Too much energy
When does alpha emission occur?
Occurs when nuclei are too massive to be stable - the strong nuclear force doesn’t have the range to hold large nuclei together
E.g. Uranium and radium
When does beta-minus occur?
Beta minus decay occurs in nuclei that are ‘neutron rich’ - have more neutrons than protons
When are gamma rays produced?
After decays the nucleus is often still excited - this energy is released as gamma rays
No change in nuclear constituents but a loss in energy
Also produced when the nucleus captures one of its own orbiting electrons
Energy of emitted radiation and half-life
There is an inverse relationship between half life and energy of emitted particles
So the lower the energy the longer the half life
