Radiation Basics
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 reaction take place continuously on the sun and all stars. The emitted radiation travels though space, and a small fraction reaches Earth. Natural sources of ionizing radiation also exist in people and in the ground. The most common of these are uranium and its decay products.
Ionizing radiation is categorized into four types:
- X-rays are manmade radiation produced by bombarding a metallic target with electron at a high speed in a vacuum. X-rays 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 called photons. The energy of X-rays are millions of time greater than that of light and radio waves. Because of this high energy, X-rays penetrate a variety of material, including body tissue.
- Gamma rays are almost identical to X-rays. Gamma rays generally have a shorter wavelength than X-rays. Gamma rays are very penetrating: thick lead is required to stop them.
- Beta radiation: A beta particle consists of an electron emitted from an atom. Is has more mass and less energy than a gamma ray, so it doesn't penetrate matter as deeply as gamma and X-rays.
- Alpha radiation: An alpha particle consists of two proton and two neutron, the same as the nucleus of a helium atom. It generally can travel no more the 1 to 3 inches in air before stooping, and can be stopped by a piece of paper.
- Decay: When an atom emits an alpha or beta particle or 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-ionizing, form. For example: U-238 has 14 different stages of decay before it stabilizes.
- An element may have several forms, or isotopes. A radioactive isotope of an element may be called "radioactive". However, the correct term is radionuclide.
- Half-life: Each radionuclide has a characteristic half-life, which is the time require for half of the quantity of material to decay.
Radiation Units of Measurement
Several different units are used to measure radiation, exposure to it and dosage.
- Roentgen: A roentgen is the amount of x-radiation or gamma radiation that produces on electrostatic unit of charge in on cc of dry air at 0 degrees C and 760 mm of mercury atmospheric pressure.
- rad: A rad is the unit of exposure to ionizing radiation equal to an energy of 100ergs per gram of irradiated material. This is the approximately equal to 1.07 roentgen.
- rem: A rem is the dosage received from the exposure to a rad. It is the number of rads multiplied by the quality factor of the particular source of radiation. The rem and millirem are the commonly used measurement unit of radiation dose in the U.S. 1 rem 1=1 rad
- Sievert: A sievert is the standard international measurement of dose. One sirevert is equivalent to 100 rem. A microsievert (mSv) is one millionth of a sievert.
curie:
A curie is the amount of radioactive material that decay at a rate of 37 billion disintegration per second, approximately the decay rate of one gram of radium. Microcuries (millionths of a curies and picocuries (trillionths of a curies) are also often used as units of measurement.
