All the stars, including the sun, emit radiation. Terrestrial sources, such as a nuclear reactor or an atom bomb, also produce radiant energy. This radiation travels through space in a straight line till it is reflected, deflected or absorbed when it encounters some other entity. The most penetrating forms of radiation can pass right through solid objects. Some kinds are more penetrating than others.
Types of Radiation
Two basic types of radiation exist: energetic particles and packets of energy called photons. Particle radiation includes alpha particles, beta radiation, neutrinos, cosmic rays and a host of recently discovered subatomic particles, such as the muon. Radiant energy photons, also called electromagnetic waves, include radio waves, microwaves, infrared waves, visible light waves, ultraviolet waves, X-rays, and gamma rays.
Particle Radiation Penetration
An alpha particle consists of two protons and two neutrons. Paper can stop this bulky particle. Beta particles penetrate matter more effectively than alpha particles. However, since beta particles are actually electrons, their electrical charge impedes their penetrating ability, and they quickly lose their energy, so that such materials as wood, plastic and aluminum can stop beta radiation. Primary cosmic rays, which consist mostly of protons, cannot penetrate the earth’s atmosphere. However, when primary cosmic rays interact with atmospheric particles, they produce penetrating secondary cosmic rays, especially muons. Muons penetrate the denser portions of the earth’s atmosphere, reach the surface and even penetrate ocean waters to a considerable depth.
Electromagnetic Radiation Penetration
Electromagnetic waves readily penetrate the atmosphere. Even the less energetic radio waves from outer space reach the surface of the earth. Electromagnetic radiation with shorter wavelengths penetrates materials most effectively. X-rays have very short wavelengths, so they can penetrate the soft tissues of the human body. Gamma rays, which have the shortest wavelengths of all electromagnetic radiation, have even greater penetrating power. It takes “several centimeters of lead or more than a meter of concrete” to stop them, according to the Duke University Department of Chemistry.
The Most Penetrating Radiation
Particles called the neutrinos have no electrical charge and no measurable mass. Neutrinos are the most penetrating type of radiation. Their penetration powers are so great that “a neutrino has to pass through many ‘light years’ of matter to have a 50-50 chance of interacting" with the nucleus of some atom, according to “The New Quantum Universe” by Tony Hey and Patrick Walters. They can easily pass straight through the earth.