RADIATION
What Are Some Sources of Radiation Exposure?
Radiation is energy that comes from a source and travels through space and may be able to penetrate various materials. Light, radio, and microwaves are types of radiation that are called nonionizing. The kind of radiation discussed in this document is called ionizing radiation because it can produce charged particles (ions) in matter.
Ionizing radiation is produced by unstable atoms. Unstable atoms differ from stable atoms because unstable atoms have an excess of energy or mass or both. Radiation can also be produced by high-voltage devices (e.g., x-ray machines).
Atoms with unstable nuclei are said to be radioactive. In order to reach stability, these atoms give off, or emit, the excess energy or mass. These emissions are called radiation. The kinds of radiation are electromagnetic (like light) and particulate (i.e., mass given off with the energy of motion). Gamma radiation and x rays are examples of electromagnetic radiation. Gamma radiation originates in the nucleus while x rays come from the electronic part of the atom. Beta and alpha radiation are examples of particulate radiation.
Interestingly, there is a "background" of natural radiation everywhere (ubiquitous) in our environment. Ubiquitous background radiation comes from space (i.e., cosmic rays) and from naturally occurring radioactive materials contained in the earth and in living things.
Types of radiation
· Alpha Particles
o Different forms of radiation may be emitted from an unstable radioactive nucleus. Energy is released and a new, more stable nucleus is formed. The 3 types of radiation to be considered in this section are: alpha, beta and gamma radiation. An alpha particle can be considered as a helium nucleus. Helium has 2 protons and 2 neutrons in its nucleus. If both of its electrons were removed, the result would be an alpha particle:
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o Since there are two protons and no electrons, alpha particles are positively charged. Alpha particles are not very penetrating. Paper, clothing or a few centimeters of air can effectively shield against alpha particles. However, if ingested or inhaled, alpha particles can be hazardous.
· Beta Particles
o Beta particles are high-speed electrons emitted from the nuclei of decaying radioisotopes. Since these are electrons, they have a negative charge and a small mass, approximated as 0 amu.
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o Beta particles may travel 2 or 3 meters through air. Heavy clothing, thick cardboard or one-inch thick wood will provide protection from beta radiation.
· Gamma Radiation
o Gamma radiation is very much like x rays. It has no charge, a very short wavelength and high energy. Gamma radiation is the most penetrating form of radiation considered in this section. It travels great distances through air (500 meters). To be protected from a gamma emitter, thick sheets of lead or concrete are required.
o Besides alpha, beta and gamma radiation, other types of particles have been found to be emitted by radioactive isotopes. Examples of these other partilcles are: protons, neutrons and positrons. We have already studied protons and neutrons. A positron is a particle emitted from the nucleus that has the same mass as an electron but has a positive charge.
· The positron is represented by the symbol:
· Nuclear Radiation
NAME
CHARGE
SYMBOL
SHIELD
DISTANCE TRAVELED
alpha
positive
paper or clothing
2-4 cm
beta
negative
heavy clothing
2-3 m
gamma
neutral
g
lead or concrete
500 m
Possible side effects of radiation therapy
Fatigue
Fatigue is an extreme tiredness that does not get better with rest. It’s a common effect of radiation, but the exact cause is unknown. Sometimes tumors cause the immune system to make substances that lead to fatigue. Fatigue may also be caused by anemia (a low red blood cell count), poor nutrition, pain, certain drugs such as steroids or chemotherapy, depression, and stress.
There’s no single treatment for fatigue, but if a cause can be found it should be treated. For example, if the fatigue is caused by anemia, some patients may benefit from blood transfusions or from medicines that cause the body to make more red blood cells.
Fatigue can last for a long time after treatment is over and some people never have as much energy as they did before treatment. Light or moderate exercise with frequent rest breaks may help to reduce fatigue. Talk with your doctor about this and other treatments that might work for you.
You can learn more about fatigue and how to deal with it in our documents called Fatigue in People With Cancer andAnemia in People With Cancer.
Skin changes
Radiation therapy today causes less skin damage than it did in the past, but your skin might still show a response to treatments. During the first 2 weeks of treatment, you might notice a faint redness. Your skin may become tender or sensitive. A few people have blistering of the outer skin layer, with some weeping until it heals. Dryness and peeling may occur in 3 to 4 weeks. After that, the skin over the treatment area may become darker. This is because of the effect radiation has on the cells in the skin that produce pigment (color). You could also lose hair in the skin over the area that is being treated.
The skin in the treatment area may also become dry and itchy. Moisturizing the skin with aloe vera, lanolin, or vitamin E may help. But before using any skin products during treatment, ask the radiation doctor or nurse if it’s OK. Some lotions that are safe to use after treatment ends can actually make things worse during treatment.
Do not use perfumes, deodorants, and skin lotions that contain alcohol or perfume on the treated area. Also avoid powders unless your doctor or nurse says they’re OK to use. Stay out of the sun as much as you can. If you must be outdoors, wear a hat and clothes that will protect your skin. After about a month of treatment, some people getting radiation may notice skin peeling and moist (weeping) areas. Let your medical care team know if this happens to you.
Later effects of radiation may include thinning of the skin. The skin may feel hard, especially if surgery has also been done in the same area. Some people may have trouble with wound healing in the area that was treated. The skin in the treatment area may always be more sensitive to the sun, and you should be extra careful to protect it when you are outdoors.
Mouth and throat problems
Mucositis (inflammation inside the mouth and throat) is a short-term side effect that can happen when radiation is given to the head and neck area. It can make swallowing painful, and some patients lose weight because they have trouble eating. It usually gets better within a few weeks after treatments end. Dry mouth and a loss of taste can be caused by radiation damage to the salivary glands and taste buds. Thick, sticky, rope-like saliva and swallowing problems may develop, too. These side effects often go away after treatments end, but sometimes they don’t.
Medical applications
Many of us are aware of the widespread use of radiation in the medical community. It can be used for diagnosis as well as therapy for a number of diseases.
In diagnostic treatments, x-rays can provide images for identifying abnormal changes in body organs and tissues. With advanced imaging and computing technologies, a three dimensional picture or animation can be generated to facilitate the diagnostic treatment if radioisotopes are injected or ingested into the patient. The most widely used diagnostic radioisotope is technetium-99m which has a half-life of six hours and releases g rays during radioactive decay. While giving the patient a very low radiation dose, technetium-99m allows sufficient time for the diagnosis process.
In therapy treatments, a radioisotope of iodine, iodine-131, is used to treat thyroid cancer. For some cancers, g rays from cobalt-60 sources are used to destroy cancer cells. Irradiating a tumour with ionizing radiation has proved to be effective in inhibiting the tumour's growth or even destroying it.
Nowadays, many medical utensils are sterilized by g rays from cobalt-60 sources. This technique is much cheaper and more effective than steam sterilization. Disposable syringe, cotton wool and surgical consumable are good examples. Since it is not a high temperature treatment process, it can be used to sterilize a range of heat-sensitive items such as plastics. In addition, as g rays have very high penetrating power, the sterilization process can be done after the item is packaged. This ensures that the item is free from bacteria before being used.
Since the discovery of anthrax-laden mail in US in October 2001, US Government uses x-rays in the same manner as in medical usage to sterilize suspected items sent through mail to avoid panic in the country.
Radio Active Isotopes
There are certain processes in nature that produce many of the naturally occurring radioactive isotopes. Other radioactive isotopes are only available by artificial production. These can be produced from nuclear reactors and high energy particle accelerators like Jefferson Lab. Radioactive isotopes are produced by bombarding a target with charged particles that are boosted in energy by an accelerator. Cyclotrons are one of the most common accelerators used for this purpose. Cyclotrons accelerate protons to hit a target to produce positron emitting radioisotopes, e.g. fluorine-18.
Industrial and agricultural applications
In industrial applications, g rays with high penetrating power are used to image defects in welds and metal castings. In addition, radiation is widely used in automatic quality control systems in production lines, such as to gauge fluid level in beverage cans or density of tobacco in cigarettes. It is also used to measure the thickness of electroplates and to eliminate static charges in industries.
In agricultural applications, radioisotopes are usually used as tracers. Fertilizers doped with radioisotopes provide a means to find out the amount of fertilizer uptaken by crops and the portion that is lost. In addition, radiation can be used to exterminate insects. Sterile Insect Technique (SIT) is applied to inhibit the reproducing power of the insects so as to reduce their population. The SIT operations conducted in Mexico were successful in reducing the number of pest/insects significantly. With the support of the United Nations Food and Agriculture Organisation (FAO) and the International Atomic Energy Agency (IAEA), the SIT programmes are underway in a number of countries.
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