E.3 Radioactive decayIB Physics SL: Flashcards
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What are isotopes?
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- What are isotopes?
- Nuclides with the same proton number but different numbers of neutrons.
- Define mass defect.
- Total mass of the separate nucleons minus the mass of the nucleus.
- Define binding energy.
- Energy needed to separate a nucleus completely into its individual nucleons.
- How do you convert a mass defect in u into energy?
- Multiply by 931.5 to get MeV.
- Where does binding energy per nucleon peak?
- Around iron-56 / nickel-62, at about 8.8 MeV.
- Properties of the strong nuclear force?
- Attractive between all nucleons, short range (~10⁻¹⁵ m), stronger than electrostatic repulsion at that range.
- What changes in alpha decay?
- A falls by 4 and Z falls by 2.
- What happens in β⁻ decay?
- A neutron becomes a proton; an electron and an antineutrino are emitted; Z rises by 1.
- What happens in β⁺ decay?
- A proton becomes a neutron; a positron and a neutrino are emitted; Z falls by 1.
- What changes in gamma decay?
- Only the energy of the nucleus: A and Z are unchanged.
- Rank alpha, beta and gamma from most to least ionising.
- Alpha, beta, gamma (the reverse order for penetration).
- What do 'random' and 'spontaneous' mean for decay?
- Random: which nucleus decays next cannot be predicted. Spontaneous: not affected by external conditions.
- Define half-life.
- Time taken for half the undecayed nuclei (or the activity) to halve.
- How do you deal with background radiation?
- Measure the count rate with no source and subtract it from every reading.