Half-lifeState that radioactive decay is a randomand spontaneousprocess and that the rate of decay decreases exponentially with time.As we have seen, some nuclides are unstable.What this means is that an unstable nucleus may spontaneouslydecay into another nucleus (which may or may not be stable).Given many identical unstable nuclides, which precise ones will decay in any particular time is impossible to predict.In other words, the decay process is random.But random though the process is, if there is a large enough population of an unstable nuclide, the probability that a certain proportion will decay in a certain timeis well defined.Topic 7: Atomic and nuclear physics7.2 Radioactive decay

Half-lifeState that radioactive decay is a randomand spontaneousprocess and that the rate of decay decreases exponentially with time.Topic 7: Atomic and nuclear physics7.2 Radioactive decayEXAMPLE: Here we have a collection of unstable Americium-241 nuclides. We do not know which particular nucleus will decay next.All we can say is that a certain proportion will decay in a certain amount of time.

Half-lifeState that radioactive decay is a random and spontaneous process and that the rate of decay decreases exponentiallywith time.Obviously the higher the population of Americium-241 there is, the more decays there will be in a time interval.But each decay decreases the population.Hence the decay rate decreases over time for a fixed sample.It is an exponential decreasein decay rate.Topic 7: Atomic and nuclear physics7.2 Radioactive decayTime axis241Am remaining

Half-lifeDefine the term radioactive half-life.We call the time it takes half of the population of an unstable nuclide to decay the radioactive half-lifeof that nuclide.Thus the previous graph had the time axis in increments of half-life.From the graph we see that half of the original 100 nuclei have decayed after 1 half-life.Thus after 1 half-life, only 50 of the original population of 100 have retained their original form.And the process continues…Topic 7: Atomic and nuclear physics7.2 Radioactive decayTime (half-lives)N (population)

RadioactivityDefine the term radioactive half-life. Rather than measuring the amount of remaining radioactive nuclide there is in a sample (which is hard to do) we measure instead the decay rate (which is much easier).Decay rates are measured using various devices, most commonly the Geiger-Mueller counter.Decay rates are measured in Becquerels(Bq).Topic 7: Atomic and nuclear physics7.2 Radioactive decay1 Becquerel1 Bq = 1 decay / second

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- Spring '16
- jane smoth
- Radioactive Decay, Henri Becquerel, nuclide