Beta decay is a type of radioactive decay where an unstable atomic nucleus transforms into a more stable one by emitting a beta particle. This beta particle can be either an electron or a positron, depending on the type of beta decay. During this process, a neutron in the nucleus changes into a proton, or vice versa, altering the element's atomic number and creating a new element. This transformation is crucial in the field of nuclear physics and helps scientists understand how elements change over time. Beta decay plays a significant role in processes like nuclear fission and is also used in various applications, including medical imaging and radiotherapy.