Half-Life Flashcards
All 5 cards in this deck
What is the half-life of a radioactive isotope?
The time it takes for the number of nuclei of the isotope in a sample to halve, or for the count-rate (activity) to fall to half its initial level.
What happens to the activity of a sample after one half-life has passed?
It falls to half its previous value.
What are the steps to find the half-life from a graph of count-rate against time?
e.g. the graph starts at 80 counts per second
- Read the starting count-rate: 80 counts/s
- Halve it: 40 counts/s
- Read off the time when the curve reaches 40 counts/s — that time is the half-life.
True or false? After two half-lives a radioactive sample has completely decayed.
False. A quarter of the original nuclei remain undecayed.
True or false? The half-life of an isotope stays the same as the sample decays.
True. Half-life is a fixed property of the isotope.