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Saturday, February 19, 2005

Chemistry radioisotopes assignment

take whatever you want: biblio is at the end
have fun!

Radioisotopes assignment

Cobalt-60
Chemical symbol
1. Use
In medicine: gamma rays released are used in radiotherapy to treat cancer.
2. Production
Produced as a by-product of nuclear reactor operations, when structural materials, such as steel, are exposed to neutron radiation
3. How used
Co-60 releases gamma rays because it has an unstable nucleus. Unstable nuclei spontaneously emit radiation as they are transformed back to a stable state (ie. As Co-60 decays to Ni-60). High intensity gamma radiation will kill cells. It is used in a technique called radiotherapy to treat cancer by targeting the cancer cells with a beam of radiation and then rotating the source of the beam. The normal cells receive a lower dose of gamma radiation than the cancer cells, where all the rays meet. Radiotherapy aims to kill the cancer cells while doing as little damage as possible to healthy normal cells.
4. a) Benefits
The half-life of cobalt-60 is 5.27 years. This is short enough to make isolation a useful treatment strategy for contaminated areas. In some cases, simply waiting 10 to 20 years allows for sufficient decay to make the site acceptable for use again.
4. b) Problems
All ionising radiation, including that of cobalt-60, is known to cause cancer. Therefore, exposures to gamma radiation from cobalt-60 result in an increased risk of cancer. The magnitude of the health risk depends on the quantity of cobalt-60 involved and on exposure conditions (length of exposure, distance from the source, whether the cobalt-60 was ingested or inhaled). Because of their metallic housings, sources of Co-60 can get mixed in with scrap metal and pass undetected into scrap metal recycling facilities. If melted in a mill, they can contaminate the entire batch of metal and the larger facility, costing millions of dollars in lost productivity and cleanup costs.


Caesium-137
Use: In industry: in levelling gauges.
Produced: Produced when uranium and plutonium absorb neutrons and undergo fission, eg. in nuclear reactors and nuclear weapons. The splitting of uranium and plutonium in fission creates numerous fission products, including Cs-137
How used: Cs-137 releases gamma rays because it has an unstable nucleus. Unstable nuclei spontaneously emit radiation as they are transformed back to a stable state. Radiation emitted from Cs-137 will be reduced in intensity by matter between the radioisotope and a detector. The amount of this reduction can be used to gauge the presence or absence of the material, or even to measure the quantity of material between the source and the detector.
Benefits: In gauging, there is no contact with the material being measured, therefore no radioactive contamination. Because it has a half-life of 30 years, Cs-137 can be used many times without needing to be replaced, thus reducing costs in industry.
Problems: Caesium-137 can be mistaken for potassium by living organisms and taken up as part of the fluid electrolytes. This means that it is passed on up the food chain and reconcentrated from the environment by that process. This makes the cleanup of caesium-137 difficult, as it moves easily through the environment. The half-life of caesium-137 is 30.17 years, which is relatively long, especially if it enters a living organism, because like all radionuclides, exposure to radiation from caesium-137 results in increased risk of cancer. Caesium-137 is an inorganic salt, and is highly soluble in water. If a leak were to develop in a storage facility, the radioactive material could easily contaminate surrounding water.

Others:
Iodine-131
(a by-product from nuclear fission in nuclear reactors)

Use
For a number of medical procedures, including to monitor and trace the flow of thyroxin from the thyroid.

Benefits
With its short half-life of 8 days, it is essentially gone from a body in less than three months.

Problems
It emits fairly high-energy beta particles and a number of gamma rays. The gamma rays are of sufficient energy to be measured outside the body if deposited in tissue such as the thyroid. Because iodine selectively deposits in the thyroid, the primary health hazard for iodine is thyroid tumours resulting from ionising radiation emitted.


Strontium-90
(a by-product from nuclear fission in nuclear reactors)

Use:
In thickness gauges (for paper, cardboard) because of its release of beta particles – the penetration of these particles indicates the thickness of a material.

Benefits:
Has a half-life long enough for repeated use (28 years).

Problems:
Strontium is radioactive, and decays very slowly, so if exposed, it will take 28 years to decay. Strontium-90 mimics the properties of calcium and is taken up by living organisms and made a part of their electrolytes as well as deposited in bones. As a part of the bones, it is not subsequently excreted like caesium-137 would be. It has the potential for causing cancer or damaging the rapidly reproducing bone marrow cells.

6. Use available evidence to analyse benefits and problems associated with the use of radioactive isotopes in identified industries and medicine.

Radioactive isotopes of various elements can be used for a range of purposes, and have the potential to be very efficient and useful, but their use must be balanced against the dangers that are inherent in handling any sort of radioactive material.
In medicine the isotope cobalt-60 is used to treat cancer. Its high intensity gamma radiation is directed at the malignant cells and is used to kill these cells, while trying to minimise damage to healthy cells. As with any radioisotope, exposure to gamma radiation may also damage healthy tissue, and this is one of the risks to be considered when undergoing radiotherapy for cancer. Another medical isotope is iodine-131, used to monitor the efficiency of the human thyroid. It is used to trace the flow of thyroxine to the gland, and is of great help when trying to diagnose thyroid-related problems. It has a short half-life (8 days) and this means that any exposure to radiation from this source will only be minimal and over a short period of time. However, the gamma rays emitted from iodine-131 are strong enough to be measured outside the body once in the thyroid, and this means that the radiation is still strong enough to cause damage to cells. Because iodine-131 is still used in diagnosing thyroid problems, it can be seen that the usefulness and efficiency of this method of testing outweighs the potential dangers in the eyes of the medical industry.
In industry, the gamma radiation produced by the radioisotope caesium-137 is used in levelling gauges to ensure that materials are level. The amount of gamma radiation that penetrates the material depends on the amount of material there is between the source of the radiation (in this case caesium-137) and the detector. In much the same way, strontium-90 is used as a thickness gauge for other, thinner materials. Here, instead of measuring the amount of gamma rays penetrating the material, beta particles are measured. Both of these industrial isotopes are created as by-products from the nuclear fission of elements such as uranium or plutonium, in nuclear reactors or from nuclear weapons. These types of nuclear reactions can be quite risky in themselves, and although many safety measures are in place at nuclear reactors around the world, it only takes one bad accident to have far-reaching and long-lasting effects (eg. Chernobyl 1986). In particular, both strontium-90 and caesium-137 can be mistaken by the body as calcium and potassium respectively, and are taken into the body as part of fluid electrolytes. In this manner, the radiation from the isotopes directly enters the body and can begin to harm living tissue. The half-lives of these two radioisotopes are about 30 years, which is a dangerously long time for a living organism to be exposed to radiation. However, for use in industry, the lengths of these half-lives is cost effective, because the isotopes only need to be replaced about every 30 years.
Besides the risks involved in producing all of these radioactive isotopes, and the health hazards from direct contact with the isotopes, there is also an environmental issue. Co-60, I-131 and Cs-137 are all soluble in water, one of the reasons for their use in medicine. Because of this, any leaks in storage facilities could result in the contamination of surrounding water, and thus the surrounding environment. Excessive radiation exposure is harmful to all living organisms, and if radioactive sources are ingested or absorbed, radiation build-up could occur within food chains and webs.
These examples of radioisotopes used in medicine and industry are a small cross section of the all the radioactive isotopes used. Each has its merits and makes the process of diagnosis and treatment more efficient in medicine, and the process of mass production more efficient in industry. However, the benefits from using these isotopes must be balanced with careful and strict safety precautions, due to the danger involved in handling radioactive substances.


Bibliography:

“Cesium”, “Cobalt”, “Iodine”, “Strontium”, (2004)
http://www.epa.gov

“Electromagnetic Waves – Gamma Rays” (2005)
http://www.gcsescience.com/pwav46.htm

“Fission Fragments”, “Beta Decay Examples” (2005)
http://hyperphysics.phy-astr.gsu.edu

“Medical and Industrial Radioisotopes” (2004)
http://www.ansto.gov.au/ari/brochures_misc/rad2.html

“Nuclear Data Section” (2004)
http://www-naweb.iaea.org/napc/nd/index.asp

“Radioisotope Brief – Cesium-127” (2004)
http://www.bt.cdc.gov/radiation/isotopes/cesium.asp

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