4 mistakes learners make with radioactivity, each one named and explained.
Decay is random, and a nucleus that decays becomes a different nucleus rather than disappearing.
You say a reactor could go off like a nuclear weapon if it were not controlled.
Both are called nuclear, and the accidents that reach the news are reported as explosions.
Question. Can a nuclear power station explode in the way a nuclear bomb does?
A common answer. yes, if the reaction runs away
The answer. no. Reactor fuel is nowhere near concentrated enough
Why. A bomb needs highly enriched fuel. Reactor fuel cannot sustain that kind of reaction.
Same word, different material. The fuel is what decides.
You say that if the half-life is two hours, one quarter will decay every hour.
Half-life is a number of hours, and numbers of hours usually divide up evenly.
Question. A sample has a half-life of 2 hours. How much has decayed after 1 hour?
A common answer. a quarter of it
The answer. about 29 per cent, and you cannot say which nuclei
Why. Decay is random. Each nucleus has a chance of decaying, and the halving is a pattern across huge numbers.
Halve for each whole half-life. Never divide a half-life into equal slices.
You say that after one half-life, half the sample has gone and the mass has halved.
Half-life says half, and decay sounds like something vanishing.
Question. After one half-life, what has happened to a sample?
A common answer. half of its mass has disappeared
The answer. half of its undecayed nuclei have decayed into something else
Why. The nuclei change into different nuclei. They are still there, so the mass barely changes.
Count nuclei, not grams. Decay changes what a nucleus is, not whether it exists.
You describe an alpha particle or a gamma ray as radioactive.
The two words share a root and are used loosely in everyday speech.
Question. Is a gamma ray radioactive?
A common answer. yes, gamma rays are radioactive
The answer. no. It is radiation. The source that emitted it is radioactive
Why. Radioactive describes something that emits radiation, not the radiation leaving it.
Ask which one is doing the emitting. That one gets the word radioactive.
WAJD spots these patterns in your child's answers and names the one behind their wrong answers, instead of just marking them wrong.