half-life (h f l f , häf -)
n.
1. Physics The time required for half the nuclei in a sample of a specific isotopic species to undergo radioactive decay.
Half-Life is the time required for something to fall to half its initial value (in particular, the time for half the atoms in a radioactive substance to disintegrate).
The term ‘Half Life’ is mainly used when talking about radioactivity: If it takes eight minutes to get the half life of a radioactive isotope of thorium. Therefore, if there are 100 grams of isotope present, in eight minutes there will be fifty. In sixteen minutes, twenty five. In twenty four minutes, twelve and a half…
However, this is not the only area or topic in which you can find an example of half-life. There is always a half life when describing an exponential-decay process.
- The current flowing through an RC Circuit.
- The first order chemical reaction, the half life would be the reactant.
Formulas for half-life in exponential decay
An exponential decay process can be described by any of the following three equivalent formulas:
Where:
- Nₒ is the initial quantity of the substance that will decay (this quantity may be measured in grams, moles, number of atoms, etc.),
- N(t) is the quantity that still remains and has not yet decayed after a time t,
- t1 / 2 is the half-life of the decaying quantity,
- τ is a positive number called the mean lifetime of the decaying quantity,
- λ is a positive number called the decay constant of the decaying quantity.
This topic was brought to us by Dr. N Cooper from Wilson’s School.
Before leaving we were reminded that at the end of next week’s session, our Parents/Carers were welcome to attend to watch all pupils receive their certificates…