Example 1
A nucleus with A=238,Z=92 emits an alpha particle. Find daughter numbers.
A decreases by 4 to 234; Z decreases by 2 to 90. The emitted alpha has A=4,Z=2, so both totals balance.
Year 11 · SACE Stage 1
Alpha, beta and gamma decay equations
Conserve nucleon number and charge in nuclear decay.
Loading saved practice…
Method and worked examples
In alpha decay, emission of a helium−4 nucleus reduces A by four and Z by two. In beta-minus decay a neutron-rich nucleus converts a neutron into a proton, electron and electron antineutrino; the daughter A stays fixed and Z increases by one. In beta-plus decay a proton-rich nucleus converts a proton into a neutron, positron and electron neutrino; A stays fixed and Z decreases by one.
Gamma emission releases nuclear excitation energy as electromagnetic radiation without changing A or Z. Write the parent and daughter numbers separately, then check charge and nucleon-number balance. The electron in beta-minus decay is created in the weak process; it is not an orbital electron expelled from a shell. Not every proposed decay is energetically allowed merely because its numbers balance.
Example 1
Example 2
A nucleus with A=14,Z=6 undergoes beta-minus decay. Find daughter numbers and emitted leptons.
The daughter has A=14 and Z=7. Emission includes an electron and an electron antineutrino; the nuclear neutron-to-proton change keeps nucleon number fixed.
Watch out: It converts a neutron into a proton and creates an electron and antineutrino in the decay process.