* Emission of energy from an atom and the transmission of this energy through space. * Energy propagated in a material medium or space.
* Energy in transit.
What are the types of radiation?
* Radiation is of two general types in our environment.
* They are called non-ionizing and ionizing.
Ionization
* the energy transferred to the electrons causes them to be pulled away or removed from an atom entirely.
*The result is the formation of an ion pair.
* The ion pair consists of a negatively-charged free electron and a positively -charged atom.
Excitation
* Process occurs when an inner electron of an atom receives enough energy to allow it to move into an excited state at a higher energy level. * However, this transfer is only temporary.
* Electron soon returns to its original energy level by re-emitting the energy gained as electromagnetic radiation. * A familiar example of excitation is the emission of light in the glass tubes in an advertising sign, commonly known as “neon signs”.
Non-Ionizing Radiation
* Non-ionizing radiation exists in various forms.
* Some are detected by our senses while other forms are recognized through special instruments that convert this type of radiation into signals that our senses can recognize. * Familiar examples
* Radio waves which carry information and entertainment through radio and television. * Microwaves which are used in microwave ovens and to transmit cellular telephone messages. * Infrared rays which provide energy in the form of heat. * Visible light which we can see
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* Ultraviolet rays from the sun which can provide a good suntan
Ionizing Radiation
* Radiation that exists in our environment.
* Unlike infrared (heat) or visible light, it is undetected by any of our physical senses. * Can be detected it with simple radiation detection instruments. * Occurs in two forms.
* rays and particles
* Occurs at the high frequency end of the electromagnetic spectrum.
Ionizing Radiation
* This type of radiation carries sufficient energy to knock electrons off other atoms – leaving them electrically charged or ionized. * In living tissues, the ions caused by such radiation can affect normal biological processes. * Because ions have an electrical charge, they are easy to detect. * This makes it possible to measure the amount of radiation present in extremely low levels.
Common types of ionizing radiation
* Alpha particles
* Beta particles
* Neutrons
* Gamma rays
* X-ray is not strictly nuclear in origin but is included here as a form of ionizing radiation very similar to gamma radiation.
* Alpha ( a ) Particles
* Have positive electric charge and are emitted from naturally-occurring elements such as uranium and radium, as well as from some man-made radioactive elements. * Made up of two protons and two neutrons bound together. * An alpha particle is identical with the nucleus of a helium atom. * Because of its relatively large size, alpha particles travel slowly. * Collide readily with matter and lose their energy quickly.
Alpha ( a ) Particles
* Have little penetrating power.
* Can be stopped by a sheet of paper or by the first layer of the skin. * Thus, present no external hazard.
* However, if they are taken in the body, for example by breathing or swallowing, alpha particles can affect the body’s cells. * Inside the body, because they give up their energy over a relatively short distance, alpha particles can inflict more biological damage than other kinds of radiation.
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Beta ( b ) Particles
* They are negatively charged particles identical to electrons. * These particles are much smaller, lighter and more penetrating than alpha particles. * They can pass through 1 to 2 centimeters of water and human flesh. * Thus, beta particles are considered a slight external hazard depending on their energy.
Beta ( b ) Particles
* However, beta particles can be stopped by a sheet of aluminum a few millimeters thick, by window glass, wood or a sheet of metal. * Beta-emitting materials can also be hazardous if taken into the body. * Examples of beta radiation are the natural radioactivity from potassium-40 in soil, rocks and minerals, and tritium, a hydrogen isotope.
Gamma ( g ) Rays
* Electromagnetic waves of very short wavelength and travelling with the speed of light. * Have greater energy than medical X-rays.
* Emitted from the nuclei of some radioactive atoms (like uranium-238) when they decay. * Very penetrating and can pass right through the human body.
Gamma ( g ) Rays
* Can be used in hospitals to diagnose and treat cancer or in industrial operations to detect defects in welds or pipes. * Dense materials such as lead and concrete are excellent barriers against gamma rays.
X-rays
* They are electromagnetic waves with lesser energy and penetrating power than gamma rays. * They are produced by machines when high-speed electrons strike a metal target and are used in many diagnostic procedures in medicine. * Can penetrate the human body, but are absorbed by denser tissues such as bone.
X-rays
* show up as the white parts on an X-ray image.
* X-rays that are not absorbed pass right through and cause the photographic film to darken when developed.
Neutrons
* Particles with no charge.
* Can penetrate many materials very easily.
* Formed during the splitting (fission) of certain atoms inside a device called a nuclear reactor. * Neutrons are not actually ionizing radiation, but if it they hit other nuclei, they may cause emission of gamma rays or charged particles, indirectly giving rise to ionizing radiation.
What are the sources of ionizing radiation?
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* The sources of radiation according to origin are natural or artificial (man-made).
* Naturally – Occurring Sources of Radiation
* The following sources of radiation constitute what we refer to as natural background radiation. The following sources of radiation constitute what we refer to as natural background radiation. * Represents about 80 percent of all the radiation to which we are exposed to.
Cosmic radiation
* We are constantly bombarded by high sub-atomic particles and gamma rays coming from the sun and outer space. * Most of it is blocked by the earth’s atmosphere, only a fraction of it reaches the ground. * Dose from cosmic radiation varies from one location to another depending on altitude, latitude and very occasionally on the solar cycle (sunspot).
Earth’s Crust (Terrestrial Radiation)
* Comes from naturally-occurring radioactive elements that have existed since the earth was formed.
* Remain radioactive for many millions of years.
* Main contributors are:
* Uranium-238
* Uranium – 235
* Thorium – 232
* Potassium-40
* Decay products which give off alpha or beta particles (and sometimes gamma rays) continuously.
Radon
* Radioactive gas that naturally comes from the radioactive decay of radium. * Radon can seep out from where they are produced into rocks or building materials of our homes. * Can then be inhaled along with its decay products.
* Radon and its decay products are the biggest source of natural radiation in the world.
Internal radiation
(food and drink)
* Since radioactive materials occur everywhere in nature, it is inevitable that they get into drinking water and food. * Potassium-40 in particular is a major source of internal radiation, but there are others. * Potassium is essential to man, plants and animals>needed by muscles
Artificial or Man – Made Sources
* Doses received from artificial sources of radiation of most people are much smaller than those from natural radiation but they still vary considerably. * Only about 20 % of man’s radiation exposure comes from artificial or man-made radioactive sources. * They are in principle fully controllable, unlike natural sources.
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Medical Applications
* The biggest man-made contribution to radiation exposure of individuals comes from the medical and dental use of X-rays and from radioactive materials used to diagnose or treat diseases. * Medical applications account for about 90 percent of all artificial or man-made radiation exposure to the general public.
Radiation in Consumer Products
* Minute radiation doses are received from artificial radioactivity in consumer products such as smoke detectors which use radioactive Americium-241 to detect smoke particles in the air. * In some luminous signs and gas mantles, fluorescence and brightness are due to the radioactive material. * The amount of radioactive material in these products are so small it does not have any effect on the consumer.
Fallout
* Radioactive fallout from nuclear weapons test carried out in the atmosphere is the most widespread environmental contaminant.
Nuclear and Other Industries
* Other artificial sources include small quantities of radioactive materials which can be released to the environment in the course of normal operation of nuclear installations. * Radioisotopes such as cobalt-60 are also used in industry to sterilize products such as cosmetics and medical supplies. * Other isotopes are used in nuclear gauges to determine the thickness of materials such as paper products, plastic films and metal sheets. * utilized to measure liquid levels in large storage tanks. * Determine the quality of welds in structures such as bridges and buildings
