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