Radioisotopes

Distinguish between a radioactive & a stable isotope. Isotopes are defined as forms of the same chemical element that have different atomic masses which is due to a varied number of neutrons. Those isotopes that do not undergo radioactive decay are called stable isotopes (mass remains the same & nuclei are stable) and those isotopes that do undergo radioactive decay are called radioactive isotopes (mass changes and nuclei is unstable which decays) and emit a particle (alpha/beta) or energy (gamma) A nucleus is said to be unstable when: * Its atomic number is greater than 83 (from bismuth onwards) * If its ratio of neutrons to protons places it outside the zone of stability. A nucleus is said to be unstable when: * Its atomic number is greater than 83 (from bismuth onwards) * If its ratio of neutrons to protons places it outside the zone of stability. Describes conditions under which a nucleus is unstable Identifies isotope and gives its symbol Technetium-99m Symbol Technetium-99m Symbol Cobalt-60 Symbol Cobalt-60 Symbol Cobalt-60 is a radioisotope of Cobalt and it is used widely in various industries, such as sterilising medical equipment and in industrial radiography. Technetium-99m is used in the medical diagnosis of patients with severe diseases such as cancer in the body. Describe how isotope is produced 2759Co + 01n 2760Co + 2759Co + 01n 2760Co + Cobalt-60 has to be produced artificially due to its short half-life of 5.26 years. In order to make it, a slow source of neutrons bombards a section of Cobalt-59 usually through water, which slows the neutrons down. It can also be produced in nuclear reactors such as the CANDU reactor, where the control rods are made of Cobalt-59. The resulting product is Cobalt-60. Technetium-99m Generator Source: www.technetium.org Technetium-99m Generator Source: www.technetium.org 4299Mo -10e + 4399m Te 4299Mo -10e + 4399m Te Technetium-99m has to be produced artificially in a small Technetium-99m generator. It is extracted from a source of Molybdenum-99 during its decay, which has a half-life of 66 hours. Due to technetium-99m having a short half-life of 6 hours, it would have to be used straight away once it has formed in the generator. Uses of Isotope Cobalt-60 is a strong emitter of gamma radiation and thus it is used in industrial radiography to examine various metal parts & welds for defects. It is also used to sterilise foodstuffs, medical equipment and supplies as well as cosmetics due to its strong radiation which effectively kill bacteria and other pathogens. It is also used medically in small amounts as a radiation source to kill cancerous cells in the body. Result of Technetium-99m Diagnostic Image Analysis, showing affected areas. (Nguyen BD, 2007) Result of Technetium-99m Diagnostic Image Analysis, showing affected areas. (Nguyen BD, 2007) Technitium-99m is the most widely used isotope in current nuclear medicine procedures due it its short half-life of 6 hours. This is effective as in small doses it can kill/ examine the cells in organs for a decent amount of time and leave the patient unaffected once it leaves the body. It can be changed to several different oxidation states, which allows it to be attached biological molecule that pinpoints the organ to be examined. For example, a pyrophosphate ion attached to Tc-99m concentrates in the calcium deposits in the heart, allowing for it to investigate the damage after a heart attack. It uses include scanning images of the brain, thyroid, lungs, liver, spleen, kidney, gall bladder, skeleton, blood pool, bone marrow, salivary and lachrymal glands and heart to detect infection. Nuclear Reactions Formation of Cobalt-60: 2759 Co + 01n 2760 Co + γ Decay of Cobalt-60: 2760 Co -10e + 2860 Ni + γ Formation of Technetium-99m: 42 99 Mo 43 99m Tc + -10e Decay of Technetium-99m: 43 99m Tc 43 99 Tc + γ Uses of the isotopes in terms of their properties Physical Properties of Cobalt-60 | Chemical Properties of Cobalt-60 | * Hard * Brittle * Grey metal with a bluish tint * Malleable | * Is radioactive * Emits powerful gamma rays (44 TBq per gram) * Melts at 1495oC * Half-life of 5.26 years | The key properties of cobalt-60 are that it emits powerful gamma radiation, has a half-life for 5.26 years (chemical properties) & is malleable (physical property). This makes it effective when searching metal parts for welds and defects; it is similar to an x-ray but is Industrial Radiography Tool (www.loknathndt.com) Industrial Radiography Tool (www.loknathndt.com) known as industrial radiography. Several beams of the gamma radiation are directed at the object from an airtight source of cobalt-60. Due to its malleability & half-life, it can be compacted into a small enough source for the industrial radiation tool and can last at least 5.26 years without being replaced. On the other side is radiographic film and when there is a crack, break or flaw the radiation passes through the radiographic film & is recorded. By analysing the film afterwards, structural problems can be detected. Cobalt-60 is also used in sterilising food and medical utensils as its powerful gamma radiation is able to kill bacteria and other pathogens without contaminating the overall state of the product, which is very useful certain industries. Physical Properties of Technetium-99m | Chemical Properties of Technetium-99m | * Silver-grey metal * High density (11g/cm-3) * Solid at room temperature | * Is radioactive * Emits low radiation gamma energy (140 keV per gram) * Melts at 3942oC * Half-life of 6 hours | Technetium-99m is the most widely used radioisotope in modern nuclear procedures due to the low gamma radiation energy it emits and also its half-life of 6 hours. This is mainly due to its chemical properties as Tc-99m can be changed into various oxidisation states. This assists the production of a wide range of biological chemicals, which in turn is attached to a biological molecule. This allows for the radioisotope to concentrate on a particular organ in the body in order to detect diseases. For example, when Tc-99m is combined with a tin (Sn) compound, it binds to red blood cells and is then carried throughout the body which can map circularity system disorders. It is a very useful radioisotope because: * Its half-life is only 6 hours. Although this is not a short length of time to be in the body, it is still reasonable for its application in diagnosing & treating patients. This is because it allows enough time for the body to absorb the isotope so infection can be detected, however to stay in the body for 6 hours emitting gamma radiation can have side-effects. * It emits low gamma radiation which minimises damage to tissues but is still able to detect disease * It is very reactive, so it can be combined which other elements to concentrate on a certain organ. Analyse benefits and problems associated with the isotope Cobalt-60 Benefits | Cobalt-60 Problems | * Exposes food to ionising radiation (gamma radiation) which kills bacteria, pathogens, moulds, insects/pests & can reduce the ripening of fruit, making it easier to transport over longer periods of time. * Allows for the detection of fractures within industrial structures by using Co-60 as a radiation source for industrial radiography * Sterilises medical equipment and food by killing all bacteria. This is because its gamma radiation is so strong. It is able to kill any unwanted organisms without contaminating the final food product or medical utensils. | * It cannot be disposed of illegally in waste lands as it can contaminate recycling facilities which can cost millions of dollars to fix. * People who are exposed to it can become very sick due to the high energy gamma radiation. This requires medical treatment. * It can get into the environment by being disposed of illegally, through leaks or spills at nuclear power plants and in solid waste from nuclear power plants. * It is very damaging to the environment; people have to wait 15-20 years until an infected site can become usable again when Cobalt-60 decays to nickel. * There is a fear that the nuclear reactors producing Cobalt-60 may become unstable. * It can be dangerous or become unstable if it is being stored in large quantities. * On-site safety is essential if people do not want to get harmed by the gamma radiation. This includes wearing PPE, such as radiation suits. | Technetium-99m Benefits | Technetium-99m Problems | * Allows for the imaging of bodily systems that would be otherwise impossible. * It can kill cancerous cells in the body with little damage to other cells. This is due to its low gamma radiation. * It has a short half-life of 6 hours, making it very useful for the medical prognoses of patients as it leaves the body within a reasonable amount of time. * It is reasonably reactive which allows it to be combined with biological molecules in order to investigate a certain organ for disease. This is so it can concentrate in a certain area, to investigate an organ such as the heart for infection/damage. | * There is a fear that exposure when treating diseases it may increase the risk of cancer. This is because although gamma radiation can kill cancerous cells, it can also cause mutations on healthy cells after exposure or treatment. * It can be difficult and dangerous to transport a radioisotope that emits gamma radiation. * It has to be used efficiently after its production due to its short half life, otherwise it is wasted. * There is a public fear of nuclear reactors & their radioisotopes. | Identify instruments and processes that can detect radiation Geiger counter (http://www.remm.nlm.gov) Geiger counter (http://www.remm.nlm.gov) There are many devices that detect radiation; however no single device can detect all forms of radiation (except for the Geiger counter). Therefore, there are different devices for each source of radiation. Some instruments & their processes include: * Geiger counter. Detects and measures amount of radiation (from alpha, beta and gamma) in the environment. The gas molecules inside the counter are excited when the smallest amount of radiation passes through them. In return, these gas molecules set up an electrical current between two pieces of metal inside, which is then connected to an amplifier. The amplifier shows the strength of the radiation present, by making “clicking” sounds. It can thus detect the Co-60 and Tc-99m gamma radiation released into the environment. * Dose Rate Meter. These measure the environmental levels of penetrating & ionising gamma radiation through an amplified current, similar to the Geiger counter. It can detect gamma rays emitted by Co-60 and Tc-99m if they have been disposed of illegally in the environment by people or nuclear power plants. * Personal Dosimeters. These are worn by humans in the form of rings or “flat badges” by persons entering an environment (mainly in medical storage facilities & nuclear power plants) containing radiation. Inside the ring is filters and film which can identify the type of radiation. The more recent dosimeters use aluminium oxide film to detect radiation, which is more effective. It can detect the gamma rays emitted by cobalt-60 that is being produced in a reactor, or where technetium-99m is being extracted. It sounds an alarm when harmful radiation is detected. Name and symbol of the transuranic elements * Uranium-238 (U) * Americium-243 (Am) Uranium Symbol Uranium Symbol Americium Symbol Americium Symbol State number of protons, neutrons and electrons Name | Protons | Neutrons | Electrons | Uranium | 92 | 146 | 92 | Americium | 95 | 148 | 95 | Explain what a transuranic element is A transuranic element is any element that has an atomic number greater than 92 (from uranium onwards); all of which have unstable nuclei and are therefore radioactive. Explains why all transuranic elements are radioactive They are all unstable because all their atoms have a greater ratio of neutrons to protons, (3:1) thus making their atomic ratio unbalanced. They all have large, unstable nuclei which in turn makes all the transuranic elements radioactive. Explains how transuranic elements are produced The transuranic elements are all produced by a process known as transmutation, which is the process of changing one element into another. There are two different ways to produce these transuranic elements: Nuclear Fission In nuclear power plants, fission occurs by colliding neutrons together with an element of high atomic mass (mainly uranium). What results is the collision of two subatomic particles. After the collision, the atomic number changes which results in the formation of a new radioisotope; this radioisotope then decays into other elements. For example, Uranium + neutrons neptunium +β plutonium + β. Nuclear fission only occurs with the elements Neptunium (93), Plutonium (94) and Americium (95) Cyclotron Accelerator (Smith, 2010) Cyclotron Accelerator (Smith, 2010) Cyclotrons This involves all the other transuranic elements from Curium and above. They are all produced by accelerating a very small, charged nucleus (such as Carbon, Boron or Helium) inside a particle accelerator to bombard and collide with a very heavy nucleus, which is often a previously made transuranic element. The result is the formation of a new transuranic radioisotope. Nuclear reactions of the transuranic elements Nuclear Reaction of Uranium: 92 238 U + 01n 92 239 U -1 0 e + 93 239 Np Nuclear Reaction of Americium: 95243 Am + 01n 95 244 Am -1 0 e + 96 244Cm Discuss the use of one transuranic element Use of Uranium for Beneficial Purposes | Use of Uranium for Hazardous Purposes | * Uranium is a fuel used to generate electricity in various power plants around the world. Almost 1/6 of the world’s total energy comes from using uranium as fuel. * Uranium is a fuel used in nuclear reactors to power some ships and submarines. * Uranium can be used in nuclear reactors to make more transuranic radioisotopes. | * Uranium is used in nuclear warfare which causes exceptional damage. This is evident from the radioactive bombings of Hiroshima and Nagasaki in Japan during World War II. * The Uranium-238 isotope has a half life of 4 billion years and eventually decays into lead. This makes it useful for nuclear fission, but extremely bad if it released into the environment as it can kill any living organisms after exposure. | Bibliography Internet Websites: Castaneda, Dianne. "What Is Nuclear Fission." Universe Today. http://www.universetoday.com/73600/what-is-nuclear-fission/ (accessed October 25, 2011). Malkoske, G.R. "Cobalt-60 Production in Candu Power Reactors." NuclearFaq. www.nuclearfaq.ca/malkoskie_cobalt_paper.pdf (accessed October 23, 2011). 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"Production of Materials." In Conquering chemistry: HSC. 4th ed. Australia : Cengage Learning, 2010. 76, 82. Books: Mulvany, Christine. "The results of mining are all around us." In Mining and Minerals- Uranium. Australia, Pages 4,5. Published by Macmillian Education , 2002. Accessed October 26, 2011. Saunders, Nigel, 2003, The Transition Metals 2: Gold, Iron and Other Elements- (The Periodic Table), Page 18, Published by Heinemann Library, Great Britain. Accessed October 26, 2011. Smith, Roland. "Production of Materials." In Conquering chemistry: HSC. 4th ed. Australia : Cengage Learning, 2010. 76, 82. Accessed October 26, 2011.