Physics - 3.8.1.3 - Radioactive decay - A Level
Argon dating
Ancient rocks contain trapped argon from decaying potassium into argon. Half life of potassium is 1250 million years.
Carbon dating
Atmospheric carbon is mostly C-12 but some C-14 from cosmic rays knocking out neutrons. Set ratio exists, with 5570 year half-life. Age or organic material can be calculated from remaining percentage.
Remaining nuclei/activity equation
(forms decay graph)
Radioactive decay
*Random* process of nuclear change
Determinants of activity
- prop. to mass of isotope - because mass decreases over time, activity decreases over time
Activity, A, equation
A = λN
Probability of nuclear decay
Constant for any nucleus
Power source for remote devices
Decaying isotope generates heat which can be used with a thermocouple to generate energy in satellites, weather sensors etc.
Power of a radioactive source
Energy transfer per second = AE, where E is energy of particles or photons released
Engine wear detection
If piston ring made from radioactive material, amount that has worn off into oil can be detected.
Activity, A, of a radioactive isotope
The number of nuclei that disintegrate per second
Decay constant, λ
The probability of an individual nucleus decaying per second
Half-life, T½
The time taken for the mass of an isotope to decrease to half the initial mass. Same as time for number of nuclei to half.
Radioactive tracer
Using short half-life isotopes to trace things in body, streams etc.
Unit of activity
becquerel (Bq) where 1 Bq = 1 decay per second
