Beta radiation is a form of ionizing radiation emitted from the nuclei of unstable atoms as they transform to a more stable state. This process, called beta decay, involves the emission of high-energy, high-speed particles.
Understanding Beta Decay
Beta decay is a nuclear process where an unstable atomic nucleus transforms, leading to the emission of a beta particle. There are two types: beta-minus (β⁻) and beta-plus (β⁺) decay.
In beta-minus decay, a neutron within the nucleus converts into a proton. This results in the emission of an electron (the beta-minus particle) along with an electron antineutrino. This process increases the atomic number by one, changing the element, while the mass number remains unchanged.
Conversely, beta-plus decay, also known as positron emission, involves a proton inside the nucleus converting into a neutron. During this decay, a positron (the antimatter equivalent of an electron, with a positive charge) is emitted, accompanied by an electron neutrino. This type of decay decreases the atomic number by one, changing the element, but the mass number stays the same. Neither the beta particle nor its associated (anti-)neutrino exist within the nucleus before decay; they are created during the transformation process.
Characteristics of Beta Particles
Beta particles are high-energy electrons or positrons emitted from an atomic nucleus. A beta-minus particle carries a single negative charge, identical to an electron, while a beta-plus particle (positron) carries a single positive charge. These particles possess a small mass, which allows them to travel at high speeds.
The range of beta particles in air varies depending on their energy, typically spanning tens of centimeters to several meters. For example, beta particles with an energy of 0.5 MeV can travel about one meter in the air, while more energetic ones around 2 MeV might travel up to 9 meters. Beta radiation has moderate penetrating power, falling between alpha and gamma radiation. It can penetrate the skin by a few millimeters and can be effectively stopped by thin layers of materials like plastic or aluminum.
Interaction with Matter and Applications
Beta particles interact with matter primarily through ionization, knocking electrons out of atoms as they pass through. This interaction causes atoms to become charged ions, and it is the fundamental mechanism by which beta radiation affects materials and living tissues. As they decelerate in matter, beta electrons can also emit secondary X-rays, known as bremsstrahlung.
These interactions are leveraged in various practical applications. In medicine, positron emission tomography (PET) scans utilize positron-emitting isotopes, where emitted positrons interact with electrons in the body to produce gamma rays for imaging. Beta radiation is also used in industrial settings for thickness gauging. Additionally, some beta-emitting radionuclides are used in medical treatments, such as eye and bone cancer therapy, and as tracers.
Safety and Protection
Exposure to beta radiation can pose health risks, particularly if the source is external and close to the body, or if the radioactive material enters the body. External exposure can cause skin burns, similar to severe sunburn, as particles deposit their energy in shallow tissues. These “beta burns” can manifest as itching, redness, and even blistering or ulceration, with symptoms appearing hours to weeks after exposure. If beta-emitting radionuclides are ingested, inhaled, or absorbed through wounds, they can cause damage to internal cells and organs.
Protection against beta radiation involves adhering to key principles: time, distance, and shielding. Minimizing the duration of exposure reduces the absorbed dose. Increasing the distance from the source significantly decreases exposure, as radiation intensity diminishes rapidly with distance. For shielding, materials with low atomic numbers, such as plastic or thin aluminum, are effective at stopping beta particles, minimizing secondary X-rays (bremsstrahlung). Heavy clothing can also offer some protection against beta particles.