PUBLIC HEALTH STATEMENT IONIZING RADIATION
PUBLIC HEALTH STATEMENTIONIZING RADIATIONDivision of ToxicologySeptember 1999This Public Health Statement is the summarychapter from the Toxicological Profile for IonizingRadiation. It is one in a series of Public HealthStatements about hazardous substances and theirhealth effects. A shorter version, the ToxFAQs , isalso available. This information is importantbecause this substance may harm you. The effectsof exposure to any hazardous substance depend onthe dose, the duration, how you are exposed,personal traits and habits, and whether otherchemicals are present. For more information, callthe ATSDR Information Center at 1-888-422-8737.This public health statement tells you about ionizingradiation and the effects of exposure. It does not tellyou about non-ionizing radiation, such asmicrowaves, ultrasound, or ultraviolet radiation.Exposure to ionizing radiation can come from manysources. You can learn when and where you may beexposed to sources of ionizing radiation in theexposure section below. One source of exposure isfrom hazardous waste sites that contain radioactivewaste. The Environmental Protection Agency(EPA) identifies the most serious hazardous wastesites in the nation. These sites make up the NationalPriorities List (NPL) and are the sites targeted forfederal cleanup. However, it's unknown how manyof the 1,467 current or former NPL sites have beenevaluated for the presence of ionizing radiationsources. As more sites are evaluated, the sites withionizing radiation may increase. This information isimportant because exposure to ionizing radiationmay harm you and because these sites may besources of exposure.When a substance is released from a large area,such as an industrial plant, or from a container, suchas a drum or bottle, it enters the environment. Thisrelease does not always lead to exposure. Even inthe event that you are exposed, it does notnecessarily mean you will be harmed or suffer longterm health effects from exposure to ionizingradiation.If you are exposed to ionizing radiation, manyfactors determine whether you'll be harmed. Thesefactors include the dose (how much), the duration(how long), and the type of radiation. You must alsoconsider the chemicals you're exposed to and yourage, sex, diet, family traits, lifestyle, and state ofhealth.1.1 WHAT IS IONIZING RADIATION?To explain what ionizing radiation is, we will startwith a discussion of atoms, how they come to beradioactive, and how they give off ionizingradiation. Then, we will explain where radiationcomes from. Finally, we will describe the moreimportant types of radiation to which you may beexposed. Of the different types and sources ofionizing radiation, this profile will discuss the threemain types: alpha, beta, and gamma radiation.The Atom. Before defining ionizing radiation, it isuseful to first describe an atom. Atoms are the basicbuilding blocks of all elements. We have models ofan atom that are supported by measurements. Anatom consists of one nucleus, made of protons andneutrons, and many smaller particles calledelectrons. The electrons normally circle the nucleusmuch like the planets or comets circle the sun. Thenumber of protons in the atom's nucleus determineswhich element it is. For example, an atom with oneDEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health ServiceAgency for Toxic Substances and Disease Registrywww.atsdr.cdc.gov/Telephone: 1-888-422-8737Fax: 770-488-4178E-Mail: atsdric@cdc.gov
PUBLIC HEALTH STATEMENTIONIZING RADIATIONDivision of ToxicologySeptember 1999proton is hydrogen and an atom with 27 protons iscobalt. Each proton has a positive charge, andpositive charges try to push away from one another.The neutrons neutralize this action and act as a kindof glue that holds the protons together in thenucleus. The number of protons in an atom of aparticular element is always the same, but thenumber of neutrons may vary. Neutrons add to theweight of the atom, so an atom of cobalt that has 27protons and 32 neutrons is called cobalt-59 because27 plus 32 equals 59. If one more neutron wereadded to this atom, it would be called cobalt-60.Cobalt-59 and cobalt-60 are isotopes of cobalt.Isotopes are forms of the same element, but differ inthe number of neutrons within the nucleus. Sincecobalt-60 is radioactive, it is called a radionuclide.All isotopes of an element, even those that areradioactive, react chemically in the same way.Atoms tend to combine with other atoms to formmolecules (for example, hydrogen and oxygencombine to form water). Radioactive atoms thatbecome part of a molecule do not affect the way themolecule behaves in chemical reactions or insideyour body.What Ionizing Radiation Is. Ionizing radiation isenergy that is carried by several types of particlesand rays given off by radioactive material, x raymachines, and fuel elements in nuclear reactors.Ionizing radiation includes alpha particles, betaparticles, x rays, and gamma rays. Alpha and betaparticles are essentially small fast moving pieces ofatoms. X rays and gamma rays are types ofelectromagnetic radiation. These radiation particlesand rays carry enough energy that they can knockout electrons from molecules, such as water,protein, and DNA, with which they interact. Thisprocess is called ionization, which is why it isnamed "ionizing radiation." We cannot senseionizing radiation, so we must use specialinstruments to learn whether we are being exposedto it and to measure the level of radiation exposure.The other types of electromagnetic radiation includeradiowaves microwaves, ultrasound, infraredradiation, visible light, and ultraviolet light. Thesetypes of radiation do not carry enough energy tocause ionization and are called non-ionizingradiation. This profile will only discuss ionizingradiation.What Ionizing Radiation Is Not. Ionizingradiation is not a substance like salt, air, water, or ahazardous chemical that we can eat, breathe, ordrink or that can soak through our skin. However,many substances can become contaminated withradioactive material, and people can be exposed toionizing radiation from these radioactivecontaminants.How Does an Atom Become Radioactive? Anatom is either stable (not radioactive) or unstable(radioactive). The ratio of neutrons to protonswithin the nucleus determines whether an atom isstable. If there are too many or too few neutrons, thenucleus is unstable, and the atom is said to beradioactive. There are several ways an atom canbecome radioactive. An atom can be naturallyradioactive, it can be made radioactive by naturalprocesses in the environment, or it can be maderadioactive by humans. Naturally occurringradioactive materials such as potassium-40 anduranium-238 have existed since the earth wasformed. Other naturally occurring radioactivematerials such as carbon-14 and hydrogen-3(tritium) are formed when radiation from the sunand stars bombards the earth's atmosphere. TheDEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health ServiceAgency for Toxic Substances and Disease Registrywww.atsdr.cdc.gov/Telephone: 1-888-422-8737Fax: 770-488-4178E-Mail: atsdric@cdc.gov
PUBLIC HEALTH STATEMENTIONIZING RADIATIONDivision of ToxicologySeptember 1999elements heavier than lead are naturally radioactivebecause they were originally formed with too manyneutrons. Human industry creates radioactivematerials by one of two different processes. In thefirst process, a uranium or a plutonium atomcaptures a neutron and splits (undergoes nuclearfission) into two radioactive fission fragments plustwo or three neutrons. In a nuclear reactor, one ofthese "fission neutrons" is captured by anotheruranium atom, and the fission process is repeated.In the second process, stable atoms are bombardedeither by neutrons or by protons that are given a lotof energy in a machine called an accelerator. Thestable atoms capture these bombarding particles andbecome radioactive. For example, stable cobalt-59,found in the steel surrounding a nuclear reactor, ishit by neutrons coming from the reactor and canbecome radioactive cobalt-60. Any material thatcontains radioactive atoms is radioactive material.How Does a Radioactive Atom Give off IonizingRadiation? Because a radioactive atom is unstable,at some time in the future, it will transform intoanother element by changing the number of protonsin the nucleus. This happens because one of severalreactions takes place in the nucleus to stabilize theneutron-proton ratio. If the atom contains too manyneutrons, a neutron changes into a proton andthrows out a negative "beta" (pronounced bay' tah)particle. If the atom contains too many protons,normally a proton changes into a neutron andthrows out a positive "beta" particle. Some atomsthat are more massive than lead, such as radium,transform by emitting an "alpha" (pronounced al' fah) particle. Any excess energy that is left can bereleased as "gamma" rays, which are the same as xrays. Other reactions are also possible, but the finalresult is to make a radioactive atom into a stableatom of a different element. For example, each atomof cobalt-60 is radioactive because it has too manyneutrons. At some time in the future, one of itsneutrons will change into a proton. As it changes,the atom gives off its radiation, which is a negativebeta particle and two gamma rays. Because theatom now has 28 protons instead of 27, it haschanged from cobalt into nickel. In this way,unstable atoms of radioactive cobalt-60 give offradiation as they transform into stable atoms ofnickel-60.How Long Can Radioactive Material Give OffIonizing Radiation? Theoretically, it gives offionizing radiation forever. Practically, however,after 10 half-lives, less than 0.1% of the originalradioactivity will be left and the radioactivematerial will give off infinitesimally small amountsof ionizing radiation. The half-life is the time ittakes one-half of the radioactive atoms to transforminto another element, which may or may not also beradioactive. After one half-life, ½ of the radioactiveatoms remain; after two half-lives, half of a half or1/4 remain, then 1/8, 1/16, 1/32, 1/64, etc. The halflife can be as short as a fraction of a second or aslong as many billions of years. Each type ofradioactive atom, or radionuclide, has its ownunique half-life. For example, technetium-99m andiodine-131, which are used in nuclear medicine,have 6-hour and 8-day half-lives, respectively. Thenaturally occurring radionuclide, uranium-235,which is used in nuclear reactors, has a half-life of700 million years. Naturally occurring potassium 40, which is present in the body, has a half-life of13 billion years and undergoes about 266,000radioactive transformations per minute in the body.Thus, technetium-99m will remain radioactive for60 hours, and iodine-131 will remain radioactive forDEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health ServiceAgency for Toxic Substances and Disease Registrywww.atsdr.cdc.gov/Telephone: 1-888-422-8737Fax: 770-488-4178E-Mail: atsdric@cdc.gov
PUBLIC HEALTH STATEMENTIONIZING RADIATIONDivision of ToxicologySeptember 1999What Are the Three Types of Radiation? Thethree main types of ionizing radiation are calledalpha, beta, and gamma radiation. These are namedfor letters of the Greek alphabet, and they are oftensymbolized using the Greek letters alpha (α), beta(β), and gamma (γ).exposed to alpha radiation if you take radioactivematerial that produces alpha radiation into yourbody (for example, if you breathe it in or swallow itin food or drink). Once inside the body, thisradioactive material can be mixed in the contents ofthe stomach and intestines, then absorbed into theblood, incorporated into a molecule, and finallydeposited into living tissue such as the bone matrix.The alpha particles from this radioactive materialcan cause damage to this tissue.Alpha Radiation (or Alpha Particles). This type ofradiation can be called either alpha radiation oralpha particles. Alpha radiation is a particle,consisting of two protons and two neutrons, thattravels very fast and thus has a good deal of kineticenergy or energy of motion. The two protons andneutrons make an alpha particle identical to ahelium atom, but without the electrons. Although itis much too small to be seen with the bestmicroscope, it is large compared to a beta particle.The protons give it a large positive charge that pullshard at the electrons of other atoms it passes near.When the alpha particle passes near an atom, itexcites its electrons and can pull an electron fromthe atom, which is the process of ionization. Eachtime the alpha particle pulls an electron off from anatom in its path, the process of ionization occurs.With each ionization, the alpha particle loses someenergy and slows down. It will finally take twoelectrons from other atoms at the end of its path andbecome a complete helium atom. This helium hasno effect on the body. Because of their large massand large charge, alpha particles ionize tissue verystrongly. If the alpha particle is from radioactivematerial that is outside the body, it will lose all itsenergy before getting through the outer (dead) layerof your skin. This means that you can only beBeta Radiation (or Beta Particles). This type ofradiation can be called either beta radiation or betaparticles. Beta particles are high-energy electronsthat some radioactive materials emit when theytransform. Beta particles are made in one of twoways, depending on the radioactive material thatproduces them. As a result, they will have either apositive charge or a negative charge. Most betaparticles are negatively charged. They are muchlighter and much more penetrating than alphaparticles. Their penetrating power depends on theirenergy. Some, such as those from tritium, have verylittle energy, and can't pass through the outer layerof dead skin. Most have enough energy to passthrough the dead outer layer of a person's skin andirradiate the live tissue underneath. You can also beexposed to beta radiation from within if the betaemitting radionuclide is taken into the body. A betaparticle loses its energy by exciting and ionizingatoms along its path. When all of its kinetic energyis spent, a negative beta particle (negatron) becomesan ordinary electron and has no more effect on thebody. A positive beta particle (positron) collideswith a nearby negative electron, and this electronpositron pair turns into a pair of gamma rays calledannihilation radiation, which can interact with othermolecules in the body.3 months. On the other hand, long-lived naturallyoccurring uranium and potassium will remain,practically speaking, radioactive forever.DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health ServiceAgency for Toxic Substances and Disease Registrywww.atsdr.cdc.gov/Telephone: 1-888-422-8737Fax: 770-488-4178E-Mail: atsdric@cdc.gov
PUBLIC HEALTH STATEMENTIONIZING RADIATIONDivision of ToxicologySeptember 1999Gamma Radiation (or Gamma Rays). This type ofradiation can be called either gamma radiation orgamma rays. Unlike alpha and beta radiation,gamma radiation is not a particle, but is a ray. It is atype of light you cannot see, much like radio waves,infrared light, ultraviolet light, and x rays. When aradioactive atom transforms by giving off an alphaor a beta particle, it may also give off one or moregamma rays to release any excess energy. Gammarays are bundles of energy that have no charge ormass. This allows them to travel very long distancesthrough air, body tissue, and other materials. Theytravel so much farther than either alpha or betaradiation that the source of the gamma rays doesn'thave to be inside the body or near the skin. Thegamma ray source can be relatively far away, likethe radioactive materials in nearby constructionmaterials, soil, and asphalt. A gamma ray may passthrough the body without hitting anything, or it mayhit an atom and give that atom all or part of itsenergy. This normally knocks an electron out of theatom (and ionizes the atom). This electron then usesthe energy it received from the gamma ray to ionizeother atoms by knocking electrons out of them aswell. Since a gamma ray is pure energy, once itloses all its energy it no longer exists.1.2 HOW DOES RADIOACTIVE MATERIALENTER AND SPREAD THROUGH THEENVIRONMENT?Radioactive material can be released to the air asparticles or gases as a result of natural forces andfrom human industrial, medical, and scientificactivities. Everyone, with no exception, is exposedto ionizing radiation that comes from naturalsources, such as cosmic radiation from space andterrestrial radiation from radioactive materials in theground. Ionizing radiation can also come fromindustrially produced radioactive materials (such asiridium-192); nuclear medicine (such as thyroidcancer treatment with iodine-131 and thyroid scansusing iodine-125, or bone scans using technetium 99m); biological and medical research usingcarbon-14, tritium, and phosphorus-32; the nuclearfuel cycle (producing fission products such ascesium-137 and activation products such as cobalt 60); and production and testing of nuclear weapons.Radioactive material released into the air is carriedby the wind and is spread by mixing with air. It isdiluted in the atmosphere and can remain there for along time. When the wind blows across landcontaminated with radioactive materials, radioactiveparticles can be stirred up and returned to theatmosphere. Radioactive material on the ground canbe incorporated into plants and animals, which maylater be eaten by people.Water can contain man-made and naturallyoccurring radioactive materials that it dissolvesfrom the soil it passes over or through. Rain andsnow also wash man-made and naturally occurringradioactive material out of the air. Radioactivematerial may be added to water through planned oraccidental releases of liquid radioactive materialfrom sources such as hospitals, researchuniversities, manufacturing plants, or nuclearfacilities. Radioactive material can also reachsurface waters when airborne radioactive materialssettle to the earth or are brought down by rain orsnow, and when soil containing radioactive materialis washed away into a river or lake. The movementof liquid radioactive material is limited by the sizeof the bodies of water into which the radioactivematerials have drained. Like silt, some radioactivematerial may settle along the banks or in theDEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health ServiceAgency for Toxic Substances and Disease Registrywww.atsdr.cdc.gov/Telephone: 1-888-422-8737Fax: 770-488-4178E-Mail: atsdric@cdc.gov
PUBLIC HEALTH STATEMENTIONIZING RADIATIONDivision of ToxicologySeptember 1999bottoms of ponds and rivers. In public health andecological contexts, it is sometimes important todistinguish between dissolved radioactivity andradioactivity bound to suspended or settled solidparticles. Radioactive material may also concentratein aquatic animals and plants. Eventually,radioactive material in liquid runoff that goes intorivers and streams may reach the oceans (there areapproximately one million radioactivetransformations per minute of the naturallyoccurring radioactive potassium in one cubic meterof ocean water).Radioactive material moves very slowly in soilcompared to its speed of movement in air and water.Radioactive material will often stick to the surfaceof the soil. The organic material in soils can bindradioactive material, which slows its movementthrough the environment. If crops are watered withwater containing radioactive material, theradioactive material may be taken up through theroots of the plant or may contaminate the outside ofthe plant. The plants may then be eaten by bothanimals and people. Radioactive materials thatoccur naturally in the soil (uranium, radium,thorium, potassium, tritium, and others) are alsotaken up by plants, and become available for intakeby animals and people.Figure 1 shows that most of your radiation dosecomes naturally from the environment. Smallerportions come from medicine, consumer productsand other
you about non-ionizing radiation, such as microwaves, ultrasound, or ultraviolet radiation. Exposure to ionizing radiation can come from many sources. You can learn when and where you may be exposed to sources of ionizing radiation in the exposure section below. One source of exposure is from hazardous waste sites that contain radioactive waste.
Ionizing radiation: Ionizing radiation is the highenergy radiation that - causes most of the concerns about radiation exposure during military service. Ionizing radiation contains enough energy to remove an electron (ionize) from an atom or molecule and to damage DNA in cells.
Non-ionizing radiation. Low frequency sources of non-ionizing radiation are not known to present health risks. High frequency sources of ionizing radiation (such as the sun and ultraviolet radiation) can cause burns and tissue damage with overexposure. 4. Does image and demonstration B represent the effects of non-ionizing or ionizing radiation?
Ionizing & Non-Ionizing Radiation Interest in this area of potential human hazard stems, in part, from the magnitude of harm or damage that an individual who is exposed can experience. It is widely known that the risks associated with exposures to ionizing radiation are significantly greater than compa-rable exposures to non-ionizing radiation.
Non-Ionizing Radiation Non-ionizing radiation includes both low frequency radiation and moderately high frequency radiation, including radio waves, microwaves and infrared radiation, visible light, and lower frequency ultraviolet radiation. Non-ionizing radiation has enough energy to move around the atoms in a molecule or cause them to vibrate .
Ionizing radiation can be classified into two catego-ries: photons (X-radiation and gamma radiation) and particles (alpha and beta particles and neutrons). Five types or sources of ionizing radiation are listed in the Report on Carcinogens as known to be hu-man carcinogens, in four separate listings: X-radiation and gamma radiation .
The use of the term non-ionizing radiation in this document is defined as meaning non-ionizing radiation produced as a result of normal equipment use and which is at such a level that is recognized as harmful to humans. NOTE: This procedure does not cover non-ionizing radiation generated during welding, cutting, or burning activities. 1.2 POLICY
non-ionizing EMF radiation exposure safety standards are based primarily on stand-alone radiation exposures. When combined with other agents, the adverse effects of non-ionizing EMF radiation on biological systems may be more severe. Much work remains to be done before definitive statements about non-ionizing
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