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  • Understanding Radiation

    Posted on June 1st, 2009 Vadim 2 comments Link to post

    Ionizing Radiation

    Ionizing radiation is radiation that changes the structure of individual atoms by ionizing them. The ions produced in turn ionize more atoms. Substances that produce ionizing radiation are called radioactive.

    Radioactivity is a natural phenomenon. Nuclear reactions take place continuously on the sun and all other stars. The emitted radiation travels through space, and a small fraction reaches the earth. Natural sources of ionizing radiation also exist in the ground. The most common of these are uranium and its decay products.

    Ionizing radiation is categorized into four types:

    X-rays are usually man made radiation produced by bombarding a metallic target with electrons at a high speed in a vacuum. Xrays are electromagnetic radiation of the same nature as light waves and radio waves, but at extremely short wavelength, less than 0.1 billionth of a centimeter. They are also called photons. The energy of x-rays is millions of times greater than that of light and radio waves. Because of this high energy level, x-rays penetrate a variety of materials, including body tissue.

    Gamma rays occur in nature and are almost identical to x-rays, but generally have a shorter wavelength than x-rays. Gamma rays are very penetrating.

    Beta radiation. A beta particle consists of an electron emitted from an atom. Beta particles penetrate matter less deeply than gamma or x-rays, but they are biologically significant because they can be more effective than gamma radiation at disrupting cellular material.

    Alpha radiation. An alpha particle consists of two protons and two neutrons, the same as the nucleus of a helium atom. It generally can travel no more than 1 to 3 inches in air before stopping, and can be stopped by a piece of paper.

    When an atom emits an alpha or beta particle or a gamma ray, it becomes a different type of atom. Radioactive substances may go through several stages of decay before they change into a stable, or non-radioactive form.

    An element may have several forms, or isotopes. A radioactive form of an element is called a radioisotope or radionuclide. Each radionuclide has a half-life, which is the time required for half of a quantity of the material to decay.


    The following chart shows the complete decay chain for uranium 238, which ends with a stable isotope of lead. Notice that the half- life of the radionuclides in the chain range from 164 microseconds to 4.5 billion years.


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