The following features of beta particles (electrons) are crucial in their shielding.
- Beta particles are energetic electrons. They are relatively light and carry a single negative charge.
- Their mass is equal to the mass of the orbital electrons with which they are interacting. A much larger fraction of its kinetic energy can be lost in a single interaction than the alpha particle.
- Their path is not so straightforward. The beta particles follow a very zig-zag path through absorbing material. This resulting path of the particle is longer than the linear penetration (range) into the material.
- Since they have very low mass, beta particles reach mostly relativistic energies.
- Beta particles differ from other heavy charged particles in the fraction of energy lost by the radiative process known as the bremsstrahlung. Therefore for high energy, beta radiation shielding dense materials are inappropriate.
- When the beta particle moves faster than the speed of light (phase velocity) in the material, it generates a shock wave of electromagnetic radiation known as the Cherenkov radiation.
Beta radiation ionizes matter weaker than alpha radiation. On the other hand, the ranges of beta particles are longer and depend strongly on the initial kinetic energy of the particle. Some have enough energy to be of concern regarding external exposure. A 1 MeV beta particle can travel approximately 3.5 meters in the air. Such beta particles can penetrate the body and deposit dose to internal structures near the surface. Therefore greater shielding than in the case of alpha radiation is required.
Materials with low atomic number Z are appropriate as beta particle shields. With high Z materials, the bremsstrahlung (secondary radiation – X-rays) is associated. This radiation is created during the slowing down of beta particles while they travel in a very dense medium. Heavy clothing, thick cardboard, or a thin aluminium plate will protect from beta radiation and prevent bremsstrahlung production. Lead and plastic are commonly used to shield beta radiation. Radiation protection literature is ubiquitous in advising plastic placement first to absorb all the beta particles before any lead shielding is used. This advice is based on the well-established theory that radiative losses (bremsstrahlung production) are more prevalent in higher atomic number (Z) materials than low Z materials.
See also more theory: Interaction of Beta Radiation with Matter
See also calculator: Beta activity to dose rate
