In positron emission, also known as beta plus decay, a proton within an atomic nucleus is converted into a neutron, resulting in the emission of a positron. This process is commonly observed in radionuclides that have excess protons in relation to their stability.
During positron emission, the atomic number of the nucleus decreases by one because a proton is lost. Since the atomic number corresponds to the number of protons in an atom, this reduction reflects the loss of a positive charge in the nucleus.
However, the mass number of the nucleus remains unchanged during positron emission. The mass number is the sum of protons and neutrons in an atom, and although a proton is converted into a neutron, the total number of nucleons (protons and neutrons) in the nucleus remains constant. Therefore, the mass number of the atom does not change during positron emission.
To summarize, in positron emission:
- The atomic number decreases by one.
- The mass number remains the same.