Physics · nuclei · NEET
| Particle emitted | Electron (e-) | Positron (e+) |
| Change inside nucleus | Neutron becomes proton | Proton becomes neutron |
| Neutral particle emitted | Antineutrino | Neutrino |
| Atomic number Z | Increases by 1 | Decreases by 1 |
| Mass number A | Unchanged | Unchanged |
| Typical parent | Neutron-rich nucleus | Proton-rich nucleus |
No. In both beta-minus and beta-plus decay the mass number A stays the same. This is because a neutron and a proton have almost the same mass, and beta decay only converts one into the other. Only the atomic number Z changes by 1 (up in beta-minus, down in beta-plus). Since A = Z + N is unchanged, the parent and daughter are ISOBARS (same A, different Z).
A free neutron is slightly heavier than a proton, so it is unstable and decays: neutron goes to proton + electron + antineutrino. Inside a nucleus that has too many neutrons, this same conversion makes the nucleus more stable. The proton stays in the nucleus (raising Z by 1), while the electron and antineutrino are thrown out. This is why Z increases in beta-minus decay.
In beta-PLUS decay a proton becomes a neutron + positron + NEUTRINO. In beta-MINUS decay a neutron becomes a proton + electron + ANTINEUTRINO. Easy rule: the positron (antimatter of electron) travels with a neutrino, and the electron (matter) travels with an antineutrino, so each pair balances matter and antimatter. This neutral, nearly massless particle carries away the missing energy and momentum.
The electron is NOT one of the atom's orbital electrons. It is created at the instant of decay when a neutron converts into a proton. The reaction neutron goes to proton + electron + antineutrino produces a brand-new electron from the energy of the process (mass-energy equivalence). So beta particles are freshly created inside the nucleus, not pulled from the electron shells.
Because the decay produces THREE particles (daughter nucleus, beta particle, and neutrino or antineutrino). The available energy is shared among them in many ways. The neutrino carries away a variable share, so the beta particle comes out with a continuous spectrum of energies from zero up to a maximum. This continuous spectrum was the original clue that the neutrino must exist.
Parent (Z, A) goes to Daughter (Z+1, A) + electron + antineutrino. Example: carbon-14 goes to nitrogen-14 + electron + antineutrino. Mass number A stays the same, Z rises by 1.
Parent (Z, A) goes to Daughter (Z-1, A) + positron + neutrino. Example: sodium-22 goes to neon-22 + positron + neutrino. Mass number A stays the same, Z falls by 1.
Neutron-rich nuclei (too many neutrons for stability) undergo beta-MINUS decay to convert a neutron into a proton. Proton-rich nuclei (too few neutrons) undergo beta-PLUS decay to convert a proton into a neutron. Both moves push the nucleus toward the stable neutron-to-proton ratio.
Yes. A beta-minus particle is an electron and a beta-plus particle is a positron. A positron has exactly the same mass as an electron but the opposite (positive) charge. That is why NCERT calls them particles with the same mass as electrons but opposite charge.
They are ISOBARS. Beta decay keeps A the same while changing Z, so parent and daughter have equal mass number A but different atomic number Z, which is the definition of isobars.
