Question

What is a positron? What are the mass number and charge of a positron? How do the mass number and atomic number of a nucleus change when the nucleus produces a positron?

Short answer

A positron, denoted by \( e^{+} \) or \( \beta^{+} \), is an elementary particle with the same mass as an electron but with a positive charge. Its mass number is 0 and its charge is +1. When a nucleus produces a positron through positron emission, its mass number remains the same, while its atomic number decreases by 1 due to the conversion of a proton into a neutron. The nuclear reaction can be represented as \( X_{Z}^{A} \rightarrow Y_{Z-1}^{A} + e^{+} + \nu_{e} \), where \( \nu_{e} \) is the emitted neutrino.

Step-by-step solution

Definition and Properties of a Positron

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 \( \beta^{+} \).

Mass Number and Charge of a Positron

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.

Mass Number and Atomic Number Change in a Nucleus Producing a Positron

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.