Radioactive decay - waves and particles Study Guide

Some atomic nuclei are unstable, meaning they have an imbalance of protons and neutrons or too much energy. To achieve stability, these unstable nuclei undergo radioactive decay, a process where they spontaneously emit particles or electromagnetic radiation. This process changes the nucleus into a more stable form. The emissions commonly associated with radioactive decay are alpha particles, beta particles, and neutrons, along with electromagnetic radiation in the form of gamma rays.

An alpha particle consists of two protons and two neutrons, identical to a helium nucleus. When an unstable nucleus emits an alpha particle, its atomic number decreases by two, and its mass number decreases by four. Beta particles are high-energy electrons emitted from the nucleus when a neutron transforms into a proton and an electron. This increases the atomic number by one, while the mass number remains unchanged. Neutrons can also be emitted by certain unstable nuclei, typically in processes like nuclear fission. When a neutron is emitted, the mass number decreases by one, but the atomic number remains the same.

Gamma rays are high-frequency electromagnetic waves, not particles. They are emitted when a nucleus has excess energy following other decay processes (like alpha or beta decay) and transitions to a lower energy state. Gamma emissions do not change the atomic number or mass number of the nucleus, only its energy content. Understanding these different types of emissions is crucial for comprehending the effects and applications of radioactivity.

Radioactive decay results in the emission of different types of radiation: alpha particles, beta particles, and gamma rays. These emissions differ significantly in their ability to penetrate materials, which is crucial for understanding their impact and safe handling. Alpha particles, consisting of two protons and two neutrons, are the least penetrating. They can be stopped by a sheet of paper or even a few centimetres of air. Beta particles, which are high-speed electrons, are more penetrating than alpha particles. They can pass through paper but are typically stopped by a few millimetres of aluminium. Gamma rays are electromagnetic waves and are the most penetrating of the three. They can pass through many centimetres of lead or many metres of concrete, requiring thick layers of dense materials for effective shielding. This difference in penetration is directly related to their ionising power; highly ionising particles like alpha particles lose energy rapidly and therefore cannot penetrate far, while weakly ionising radiation like gamma rays can travel much further before being absorbed.