Idea 7of 7Builds onThe halving clock
Never quite zero
After four half-lives, is the sample safe to ignore?
Today you'll discover
- why halving never finishes
- how a medical tracer is chosen
- why nuclear waste plans are written in millennia
Think firstFour half-lives in. Is the tracer gone?
After four half-lives, what fraction of the tracer is still radioactive?
Decide first, then press Next. Watch whether the last bar touches the axis.
Four halvings of a bar, the last one a thin sliver still above the axis, ringed. After a prediction, the sliver is highlighted, then the faint bars above showing what has decayed, then the clock. The last step asks about plutonium waste after one half-life.
See the whole ideathe big idea and the key word, in one place
The big idea
Halving never reaches zero; it only shrinks.
Compare themShort half-life: intense now, gone soon; the right choice for a medical scan. Long half-life: faint now, present for ages; the problem with waste.
About this modelEach half-life halves what is left. Halving never reaches zero; it only shrinks.
Each half-life halves what is left. Halving never reaches zero; it only shrinks.
Ready to use it?
- Explain why a sample is never completely gone, and estimate how many half-lives make it negligible.