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A positron, also known as a positive electron, is an elementary particle with the same mass as an electron but with a positive charge. It is the antiparticle of the electron. The positron is denoted by the symbol \( e^{+} \) or \( \beta^{+} \).

The mass number (A) of a positron is 0 since its mass is approximately 9.31 x 10^-31 kg, which is negligible compared to the mass of a proton (about 1.67 x 10^-27 kg). The charge (Q) of a positron is +1, as it carries a single positive charge.

When a nucleus produces a positron, it undergoes a process called positron emission or beta-plus decay. During this process, a proton within the nucleus is converted into a neutron, a positron, and a neutrino. Let's denote the parent nucleus as \( X_{Z}^{A} \) where Z is the atomic number (the number of protons) and A is the mass number (sum of protons and neutrons). The daughter nucleus can be denoted as \( Y_{Z-1}^{A} \). During positron emission, the mass number of the nucleus (A) does not change, as the total number of protons and neutrons remains the same. However, the atomic number (Z) decreases by 1, as a proton is converted into a neutron. The nuclear reaction can be expressed as follows: \[ X_{Z}^{A} \rightarrow Y_{Z-1}^{A} + e^{+} + \nu_{e} \] where \( \nu_{e} \) denotes the emitted neutrino.