Beta particles come out with a puzzling spread of energies, unlike the sharp lines of alpha decay. The resolution was a ghostly third particle, the neutrino, carrying away the balance and saving the conservation laws.
Every particle has an antiparticle with the same mass but opposite charge; the positron is the electron antiparticle. Beta-minus decay emits an electron and an antineutrino; beta-plus decay emits a positron and a neutrino. Alpha particles leave with discrete energies, but beta particles have a continuous range, because the energy is shared with the (anti)neutrino. The unified atomic mass unit u is one twelfth of the mass of a carbon-12 atom.
Watch a neutron decay: an electron and an antineutrino fly out, sharing the available energy. Because the split varies, the electron energy spans a continuous range up to a maximum.
Same mass, opposite charge.
| Particle / process | Partner / products | Note |
|---|---|---|
| electron | positron | charge −e and +e |
| β⁻ decay | emits electron + antineutrino | from a neutron |
| β⁺ decay | emits positron + neutrino | from a proton |
Four quick checks tied to this lesson. Each correct answer earns XP and lights this skill on your star map.
The antiparticle of the electron is the:
An antiparticle has the same mass as its particle but the opposite:
In beta-minus decay, the particles emitted are an electron and:
Beta particles are emitted with a continuous range of energies because the energy is shared with:
The continuous beta spectrum looked like a violation of conservation.
An antiparticle has the same mass as its particle, only the charge is reversed; do not say it is lighter or heavier. Beta-minus decay emits an antineutrino (with the electron), while beta-plus emits a neutrino (with the positron); keep the pairing right. The unified atomic mass unit is defined from carbon-12, as one twelfth of that atom mass.
Unlocks once the checks above are done. Worth more XP, written to AS Paper 1 and 2 standard.
The continuous energy spectrum of beta particles is evidence for the existence of the:
The unified atomic mass unit (u) is defined as:
In beta-plus decay, a nucleus emits a positron and:
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