Types of Radiation
There are two chief types of radiation. One is electromagnetic radiation consisting of energy. The other type is known as particle radiation or particulate radiation consisting of tiny particles of matter.
Electromagnetic radiation travels in waves called electromagnetic waves. These waves carry energy in the form of oscillating (pulsating) electric and magnetic fields. (In physics, a field is the region through which a given force is effective.) Every electrically charged body is surrounded by an electric field. An electric field is a region where the bodys electric force can be found. In the same way, every magnetic body is surrounded by its magnetic field. The lines of force of the magnetic and electric fields are at right angles to each other. The two fields together form an electromagnetic field.
Electromagnetic waves are transverse waves, the oscillations of the electromagnetic field being at right angles to the direction of travel of the waves. Each complete oscillation of the electromagnetic field is called a cycle. The number of cycles that occur in a given time is called the frequency of the electromagnetic wave. The wavelength can be determined by dividing the speed of the wave by the wave's frequency.
Though electromagnetic radiation travels as a wave through waves, it also has the properties of particles. Atoms release electromagnet radiation in the form of photons. A photon is a tiny packet of energy, which, like particles, occupies a fixed amount of space. However, like waves, photons too have a definite frequency and wavelength. The energy of a photon depends on its frequency and wavelength. When the radiation has a high frequency and a short wavelength, its photons have high energy. If the radiation has a low frequency and a long wavelength, its photons have low energy. There are many sources of electromagnetic radiation. Materials that are being heated act as sources of electromagnetic radiation. The sun produces electromagnetic radiation from nuclear reactions in its core.
Unlike other waves, electromagnetic waves can travel through a vacuum. In a vacuum, the waves move at a speed of about 186,300 miles (299,800 km) per second. In passing through matter, the speed of the waves is reduced. For example, in water the speed of light (a kind of electromagnetic radiation) is only about three-fourths as great as its speed in a vacuum. Different kinds of radiation differ in their frequency and wavelength. The electromagnetic spectrum can be seen when white light passes through a prism and splits into all the visible colors, ranging from red to violet. The colors are formed by different wavelengths of light. They make up the visible spectrum, the part of the electromagnetic spectrum that can be seen. The electromagnetic spectrum is made up of wavelengths of all sizes, including those too long and too short to be seen.
Each kind of electromagnetic radiation occupies a band, or range of wavelengths, of the electromagnetic spectrum. There are no sharp divisions between the bands. The wavelengths of each band blend into those of adjacent bands. The approximate range of wavelengths of each band, in centimeters (a centimeter is 0.3937 inch), is as follows:
|Radio Waves||3,000,000 to .03|
|Infrared Waves||.03 to .000076|
|Visible Light||.000076 to .00004|
|Ultraviolet Waves||.00004 to .0000004|
|X Rays||.0000004 to .000000001|
|Gamma Rays||.000000001 to .000000000056|
Particle radiation consists of protons, neutrons, and electrons, which are the building blocks of an atom. It has both mass and energy. Most of the types of particle radiation travel at high speeds but they are slower than the speed of light. However, there is a type of particle called neutrino, which travels almost at the speed of light. Its mass is also undetermined. According to scientists, protons, neutrons, and electrons also behave like waves. These waves are called matter waves. Like electromagnet radiation, particle radiation too has characteristics of both particles and waves. There are four types of particle radiation—i) alpha particles, ii) beta particles, iii) protons, and iv) neutrons.
Alpha particles consist of two protons and two neutrons and have positive electric charge. These particles are identical with the nuclei of helium atoms. The mass of an alpha particle is about 7,300 times as large as the mass of an electron. Some radioactive atoms give off alpha particles.
Beta particles are electrons, which are produced when a radioactive nucleus creates and releases an electron. In the process, a neutron in the nucleus changes into a proton and a beta is released. Most beta particles are negatively charged. However, some beta particles are positively charged. These are called positrons. Positrons are a form of antimatter, matter that resembles ordinary matter except that its electric charge is reversed. Positrons are produced when an atom changes a proton into a neutron. When a positron collides with a negatively charged electron, both of them destroy each other. As a result, two or three gamma ray photons are produced. This type of collision is known as pair annihilation.
Neutrinos and antineutrinos, two other particles, accompany beta radiation. A neutrino is a particle with no charge and an undetermined mass, which is released when a nucleus produces a positron. When a nucleus produces a negatively charged beta particle, it also releases an antineutrino, which is the antimatter form of a neutrino.
Protons and neutrons can also be discharged from some radioactive nuclei. Each has a mass about 1,850 times greater than the mass of an electron. The mass of a neutron is slightly greater than the mass of a proton. Neutron radiation is more common than proton radiation, which rarely happens naturally on Earth.