Atoms are the fundamental building blocks of all substances. Their central nuclei can sometimes be unstable, leading to radioactive decay. This process transforms unstable nuclei into more stable configurations, often by emitting subatomic particles and energy.
What is a Beta Particle?
A beta particle is a high-energy electron or positron emitted from an unstable atomic nucleus during beta decay. Unlike electrons from the atom’s electron cloud, beta particles are created within the nucleus when a neutron or proton transforms. This process helps the unstable nucleus achieve a more stable state by adjusting its neutron-to-proton ratio.
The emission of a beta particle alters the atomic number of the element, transforming the original unstable atom into a different element. These particles travel at speeds approaching the speed of light.
The Two Forms of Beta Decay
The charge of a beta particle depends on the type of beta decay occurring within an unstable nucleus. There are two primary forms: beta-minus decay and beta-plus decay. Each process results in the emission of a beta particle with a distinct electrical charge.
Beta-Minus Decay (β⁻ Decay)
In beta-minus decay, an unstable atomic nucleus with an excess of neutrons transforms one of its neutrons into a proton. To conserve electrical charge, the nucleus emits a high-energy electron (the beta-minus particle) with a negative charge of -1e. An antineutrino, a neutral particle, is also emitted. This decay increases the atomic number by one, changing the element, while the mass number remains the same.
Beta-Plus Decay (β⁺ Decay)
Conversely, beta-plus decay occurs in unstable atomic nuclei with an excess of protons, where a proton transforms into a neutron. To conserve electrical charge, the nucleus emits a positron (the beta-plus particle). A positron is the antimatter counterpart of an electron, carrying a positive charge of +1e. Alongside the positron, a neutrino, a neutral particle, is released. This transformation decreases the atomic number by one, changing the element, but the mass number remains constant.
Characteristics and Behavior
Beta particles, whether negatively or positively charged, share common characteristics and behaviors. They are relatively light subatomic particles, with a mass comparable to that of an electron. These particles are emitted at very high speeds, often approaching the speed of light, carrying significant kinetic energy.
Due to their charge, beta particles interact with electric and magnetic fields. A negatively charged beta-minus particle will be deflected in one direction, while a positively charged beta-plus particle (positron) will be deflected in the opposite direction. Beta particles have an intermediate penetrating power; they can pass through thin materials like paper or a few millimeters of aluminum but are generally stopped by thicker materials like a few centimeters of plastic or wood.
Where Beta Particles Are Found
Beta particles are a natural part of radioactive decay processes in various isotopes found in the environment. For instance, Carbon-14, a naturally occurring radioactive isotope used in radiocarbon dating, decays via beta-minus emission. Potassium-40, another common isotope present in many rocks and biological systems, also undergoes beta-minus decay.
Beyond natural occurrences, beta particles are utilized in beneficial applications, particularly in medicine. Positron Emission Tomography (PET) scans rely on the emission of positrons (beta-plus particles) from a radioactive tracer. Beta particles are also used in radiation therapy for localized treatment of cancers, where their limited penetration depth allows for precise targeting of superficial tumors.