|MadSci Network: Chemistry|
Parvathy, There is the possibility of harmful events associated with all aspects of the use of radioactive materials. I am going to restrict myself to effects on humans for this discusion. The term radioactive means that the atom in question is unstable and will emit ionizing radiaton. This can be in the form of alpha particles (helium nuclei with two protons and two neutrons), beta particles (identical to a negatively charged electron), and gamma rays (high energy electromagnetic radiation). Those are the major types encountered. There are some rarer radioactive materials, or mixtures, that emit postitively charged electrons called positrons, and sources designed to emit neutrons--those are used for measurements of soil or cement density, and are in sealed units in those instruments. The negative effects are caused by the ability of "ionizing radiation" to remove electrons from atoms (hence the name "ionizing") as they interact with matter. If the matter is the human body, electrons can be removed from atoms creating charged particles, or ions, and those can interact with biological molecules damaging them so that they cannot perform their normal functions. For an overview on this subject, I suggest you read a few of the articles found by entering "interaction of radiation with matter" and "biological effects of ionizing radiation" into a search engine. The university articles, and even the Wikipedia articles are good introductions to the mechanisms. You will find that alpha particles are not a danger as long as they remain outside the body. They cannot penetrate the skin. Their danger is if they get inhaled or injected into the body. There, their energy is very disruptive to atoms over a short distance. The most common radioactime element to get into the body this was is radon, a radioactive inert gas, from the decay of naturally occurring Uranium and Thorium in the earth. This gas may be in water, cement, enter into basements from bedrock, or be in the air underground miners breathe. Long exposures to high levels of radon gas can cause lung cancer to develop after some years. Industrially, in the 1920s through the 1940s radium uas painted onto dials and indicators (like hands on a watch) because it glowed in the dark. The painters (almost all women) used to tip the brushes with their tongue to get a very fine point for painting dial markings or indicators. Over the years (these painters were followed by health physicists the rest of their lives) many suffered from cancer caused by the radiation from the radium (a bone-seeking atom when in the body) which contained alpha, beta, and gamma radiation. You can find out about their stories by searching for "Radium Dial Painters History" if you are interested in further details. Beta and Gamma radiation can affect the body from the outside because they have enough energy to get through the outer layer of the skin. Now, like any harmful agent, it is the dose that matters. Beta particles being high energy electrons have ability to ionize atoms than gamma rays (which have a probability of passing through you without interacting). Beta particles are also worse when ingested because the damage is done inside the body. From the outside, plastic or aluminum are good for shielding persons working with them. Many radioisotopes used in research in a laboratory are beta emitters, and they are sefely handled with light shielding like 3/4 inch lucite. People have worked with beta emitting materials over long times, and with the basic shielding and hygiene have had no ill effects. However, large amounts of external beta radiation will cause skin burns from ionizing the layers of the skin just as Ultra-violet rays from the sun will do. Although more shielding is needed to work with gamma emitting radionuclides, lead is one of the shields used for gamma rays, again proper techniques, shielding, and hygiene will make the workplace safe. One of the industrial uses of large gamma emitting sources is radiography. Gamma rays are high energy X-rays, and can be used to take Gamma Radiographs of objects using photographic film. The source is in a lead shield. This unit is placed on a holder in the center of a large welded pipe--such as on an oil or gas pipeline. Film is placed on the outside of the pipe all around the weld. The radiographer can cause the source to be moved out of its shield on a wire that is welded to the source and unwinds from the back of the shield. The source is left out for the amount of time necessary to radiograph the welds to look for voids or other defects that could cause the weld to fail. After that time has passed (with all workers, including the radiographer, away from the source), the radiographer winds the source back into its shield. Sometimes the source gets stuck without going all the way into the shield. Radiographers have gotten burns and radiation exposures from those incidents. While excessive exposures are negative effects, we live in a sea of radiation all the time. This is the background radiation from the radioactive materials in the earth, cosmic radiation (more radiation at higher altitudes because the atmosphere didn't absorb as much), and medical uses of radiation (x-rays (including fancy scanning like full- mouth scans at a dentist or CAT, computed axial tomagraphy), radiactive materials injected for tests or treatment. One thing to remember is that life on this planet has developed over a very long time. While life was first forming, the level of radiation from the planet, the background radiation at that time, was much greater than it is today. The radioactive materials in the earch today have ha;f-lives on the order of the age of the earth. All of those radioactive elements with half lives shorter than about one tenth the age of the earth have decayed away. If you look at a chart of the radioactive nuclides, you will see that radium and radon are very short lived with respect to the age of the earth--however, they are being continuously formed by the decay of uranium and thorium nuclides that are a long-lived as the age of the earth (you can find the math for this by searching "Radioactive Serics Decay" or "Uranium Decay Series". Absent large doses from medical or other non-natural radiation, we actually live in a lower background radiation that when life developed. I hope this answers your question about negative effects, and puts some of the natural radiation into perspective for you.
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