What is radioactivity? What does it mean for an atom to be radioactive?

Radioactive decay is a fascinating and fundamental process in which an unstable atomic nucleus releases energy to reach a more stable state. This spontaneous transformation can occur in multiple ways – by emitting alpha particles, beta particles, gamma rays, or even neutrons. Think of it like popcorn kernels in a microwave; the unstable 'kernels' (atomic nuclei) pop and transform into different 'flavors' (atoms of different elements or isotopes) as they release energy.

Each type of decay results in the creation of new substances, which could have applications in various fields like medicine, energy, and archaeology. For example, carbon-14 decays over time, which helps archaeologists date ancient organic materials.

Imagine an alpha particle as a tiny, high-speed projectile. It's composed of two protons and two neutrons, which are the same as a helium-4 nucleus. These particles are ejected from the radioactive nucleus during alpha decay, but they can't travel very far or pass through much material – even a sheet of paper or the outer layers of human skin can stop them.

Despite their limited penetration power, alpha particles can be harmful if they come into contact with living tissue internally, such as being inhaled or ingested, because they can cause significant cellular damage.

Beta particles, on the other hand, are much smaller than alpha particles. There are two types of beta decay, known as beta-minus and beta-plus. In beta-minus decay, a neutron turns into a proton and emits an electron – that electron is the beta particle. Conversely, in beta-plus decay, a proton is transformed into a neutron, releasing a positron, which is a particle with the same mass as an electron but with a positive charge.

Beta particles have a greater penetration power than alpha particles but are usually stopped by a few millimeters of aluminum. When they interact with materials, they can ionize atoms along their path, which can lead to chemistry changes or biological damage.

Gamma rays are not particles, but rather, high-energy photons, which are packets of electromagnetic energy. They are produced during nuclear transitions, often accompanying alpha or beta decay. Unlike alpha and beta particles, gamma rays are deeply penetrating and require dense shielding, like lead or thick concrete, to reduce their intensity.

Due to their penetrative power, gamma rays are widely used in medical imaging and cancer treatment. However, prolonged exposure to gamma radiation can be dangerous, leading to tissue damage and increased cancer risk, so proper safety measures are crucial.