Radioactive Decay and Half-Life: Flashcards
Revise nuclide notation, alpha, beta, positron and gamma decay, nuclear equations, penetrating power and half-life.
Radioactive Decay and Half-Life: Flashcards
- QuestionIn nuclide notation, what do the top and bottom numbers mean?Answer
Top: mass number A (protons + neutrons). Bottom: atomic number Z (protons). E.g. uranium-238: A = 238, Z = 92.
- QuestionWhat is an alpha particle, and how does alpha decay change the nucleus?Answer
A helium-4 nucleus (2 protons + 2 neutrons). A decreases by 4, Z by 2.
- QuestionWhat happens in beta (β⁻) decay?Answer
A neutron becomes a proton and an electron; the electron is emitted. A stays the same, Z increases by 1.
- QuestionWhat happens in positron (β⁺) emission?Answer
A proton becomes a neutron and a positron is emitted. A stays the same, Z decreases by 1.
- QuestionWhat is gamma radiation?Answer
High-energy electromagnetic radiation from an excited nucleus. A and Z do not change.
- QuestionWhat must balance in a nuclear equation?Answer
The total mass number and the total atomic number on each side.
- QuestionWhat stops alpha, beta and gamma radiation?Answer
Alpha: paper or skin. Beta: a few mm of aluminium. Gamma: only reduced by thick lead or concrete.
- QuestionDefine half-life.Answer
The time for half of the radioactive nuclei in a sample (and its activity) to decay.
- QuestionWhat fraction of a sample remains after 3 half-lives?Answer
(½)³ = ⅛, i.e. 12.5 %.
- QuestionEquation for the amount left after time t?Answer
N = N₀ × (½)ⁿ, where n = t ÷ t½ (t and t½ in the same unit).
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