In positron emission, also known as beta plus decay, a proton in the nucleus is converted into a neutron, and a positron (a positively charged electron) is emitted. This process is represented by the following nuclear equation:
Z_X^A → Z-1_Y^A + β^+ + ν_e
Here, Z_X^A represents the parent atom with atomic number Z and mass number A, Z-1_Y^A represents the daughter atom with an atomic number of Z-1 and mass number of A, β^+ represents the emitted positron, and ν_e represents an electron neutrino.
Since a proton is converted into a neutron during positron emission, the atomic number decreases by 1 in the daughter atom compared to the parent atom. However, the mass number remains the same because the total number of protons and neutrons in the nucleus does not change during this process.
To summarize:
- Atomic number (Z): Decreases by 1
- Mass number (A): Remains the same
It's worth noting that positron emission typically occurs in radioactive nuclei that have an excess of protons, which helps to stabilize the nucleus by increasing the neutron-to-proton ratio.