Nuclear Energy Dot Points
5.1 distinguish between stable and radioactive isotopes and describe the conditions under which ...
5.4 identify instruments and processes that can be used to detect radiation Covered in class notes
5.5 identify one use of...
5.5 identify one use of a named radioisotope:
- in industry
- in medicine
In medicine
5.6 describe the way in which the ab...
.
Rex Boyd defends the decision to commission a new nuclear reactor.
It is claimed by opponents of the nuclear industry th...
5.8 use available evidence to analyse benefits and problems associated with the use of radioactive isotopes in identified
...
5.8 use available evidence to analyse benefits and problems associated with the use of radioactive isotopes in identified
...
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  1. 1. Nuclear Energy Dot Points 5.1 distinguish between stable and radioactive isotopes and describe the conditions under which a nucleus is unstable. Use your class notes plus below Atoms contain protons and neutrons in a nucleus surrounded by electrons in energy level shells. Isotopes of an element are atoms of that element containing the same number of protons but different numbers of neutrons. If the nucleus of an atom contains excess energy the nucleus is unstable and can emit radiation. The radiation emitted is characteristic of the nucleus. The emitted radiation can be used in many ways in industry and medicine. • Isotopes of the same element have the same atomic number (Z). • Only 279 of about 2000 known isotopes are stable. In a stable isotope nucleus, the protons and neutrons are in a low energy level and are unable to emit radioactivity. • Radioactive isotopes are unstable. They emit radiation as they spontaneously release energy. This is called radioactive decay. An unstable isotope can be called a radioisotope, an abbreviation of the term radioactive isotope. Radioactive isotopes can emit three types of radiation: Radiation Symbol Type alpha 4 2 He particle beta 0 -1 e particle gamma high frequency electromagnetic radiation 5.2 describe how transuranic elements are produced Transuranic elements are elements with an atomic number above that of uranium with atomic number Z= 92. Twenty-two transuranic elements have been made. The claim to production of element 118 has been withdrawn by the originating laboratory as no other laboratory anywhere in the world has been able to replicate this production. Only three of the transuranic elements, those with atomic numbers 93, 94 and 95, have been produced in nuclear reactors. • When U-238 is bombarded with neutrons it can be converted to U-239 that undergoes beta decays to produce neptunium and plutonium. • Pu-239 is changed to americium by neutron bombardment. Americium-241 is used in most house smoke alarms. 5.7 process information from secondary sources to describe recent discoveries of elements. Covered in your research of 2-3 transuranic elements. 5.3 describe how commercial radioisotopes are produced. Your text book has excellent notes on Linear accelerators, cyclotrons and nuclear reactors.
  2. 2. 5.4 identify instruments and processes that can be used to detect radiation Covered in class notes 5.5 identify one use of a named radioisotope: - in industry - in medicine 5.6 describe the way in which the above named radioisotope is used and explain its use in terms of its chemical properties In industry The radionuclide, cobalt-60, is produced for commercial use in linear accelerators, however its main source is in nuclear reactors where a neutron 0 1 n combines with cobalt -59 (a non radioactive isotope of Cobalt) Cobalt-60 is used in many common industrial applications, such as in leveling devices and thickness gauges, and in radiotherapy in hospitals. Large sources of cobalt-60 are increasingly used for sterilization of spices and certain foods. The powerful gamma rays kill bacteria and other pathogens, without damaging the product. After the radiation ceases, the product is not left radioactive. This process is sometimes called "cold pasteurization." Cobalt-60 is also used for industrial radiography, a process similar to an x-ray, to detect structural flaws in metal parts. Radionuclides, such as cobalt-60, that are used in industry or medical treatment are encased in shielded metal containers or housings, and are referred to as radiation ‘sources.' The shielding keeps operators from being exposed to the strong radiation. Cobalt-60 is used in industrial radiography to inspect metal parts and welds for defects. Beams of radiation are directed at the object to be checked from a sealed source of Co-60. Radiographic film on the opposite side of the source is exposed when it is struck by radiation passing through the objects being tested. More radiation will pass through if there are cracks, breaks, or other flaws in the metal parts and will be recorded on the film. By studying the film, structural problems can be detected . Chemical properties Explaining its use 1. Co-60 is used because it is an emitter of gamma rays along with a small amount of Beta 60 27 CO 60 28 Ni + 0 -1 e + gamma rays gamma rays will penetrate metal parts Radionuclides, such as cobalt-60, that are used in industry are encased in shielded metal (lead or stainless steel)containers. Any container is registered with the government to follow its location The powerful gamma rays kill bacteria and other pathogens, without damaging the product. After the radiation ceases, the product is not left radioactive. Some countries irradiate fruits to kill bacteria. The same techniques can be used to sterilise surgical equipment. 2. Co-60 has a half-life of 5.3 years can be used in a chemically inert form held inside a sealed container. This enables the equipment to have a long lifetime and not require regular maintenance.
  3. 3. 5.5 identify one use of a named radioisotope: - in industry - in medicine In medicine 5.6 describe the way in which the above named radioisotope is used and explain its use in terms of its chemical properties Today, radioactive substances (for example radiopharmaceuticals) are very useful in medicine, as long as the dose is carefully controlled. In Australia, about 550,000 people benefit from nuclear medical procedures every year, and most people will make use of nuclear medicine at some stage in their lives Technetium 99m is an isotope of the artificially-produced element technetium and it has almost ideal characteristics for a nuclear medicine scan. These include- Chemical properties Explaining its use 1. It has a half-life of six hours which is long enough to examine metabolic processes yet short enough to minimise the radiation dose to the patient. It is quickly eliminated from the body after 24hrs nearly 95% has decayed 2. Technetium-99m decays by a process which emits low energy gamma rays and some beta 99 42 Mo 99 43 Tc + 0 -1 e + low energy gamma rays A radioisotope used for diagnosis must emit gamma rays of sufficient energy to escape from the body and minimises damage to tissues but can still be detected outside a person's body by a gamma ray sensitive camera. The radioisotope then allows the location of the tumour or the characteristics of the other tissue to be revealed. The process is one of the forms of imaging that can be used in medicine. It is called positron emission tomography (PET). This technique can even be used to show brain activity in real time. 3. Tc-99m can be changed to a number of oxidation states This enables production of a wide range of biologically active chemicals. The Tc-99m is attached to a biological molecule it can be reacted to form a compound with chemical properties that leads to concentration in the organ of interest such as the heart, liver, lungs or thyroid. Eg attached to tin and injected into the blood it binds with red blood cells so functioning of the heart and blood vessels can be observed. 4. Tc-99m is generated from the radioisotope molybdenum-99 98 42 Mo + 1 0 n 99 42 Mo 99 42 Mo 99 43 Tc + 0 -1 e + low energy gamma rays Technetium generators, a lead pot enclosing a glass tube containing the radioisotope Mo-99, are supplied to hospitals from the nuclear reactor at Lucas Heights where the isotopes are made. They contain molybdenum-99, with a half-life of 66 hours, which progressively decays to technetium-99. The Tc-99 is washed out of the lead pot by saline solution when it is required. After two weeks or less the generator is returned for recharging. NOTE – If it were made in a cyclotron, because of its short half life, it would have to be made continually. (read the article on the next page) Technetium-99m (6 h): Used in to image the skeleton and heart muscle in particular, but also for brain, thyroid, lungs, liver, spleen, kidney (structure and filtration rate), gall bladder, bone marrow, salivary glands, heart, infection and numerous specialised medical studies. Radiopharmaceuticals can be used as tracers to diagnose medical problems, or to treat certain illnesses. The tracers used in medicine are gamma emitters – they give off gamma radiation. Gamma radiation is less biologically damaging than alpha or beta, and is strong enough to escape from within the body and reach the measuring instruments outside. The gamma emitter used in about 80% of nuclear medicine diagnoses is technetium-99m. It is a very unusual but readily available radioisotope. It is formed from molybdenum-99 in a nuclear reactor and supplied to hospitals in a lead pot enclosing a glass tube containing the radioisotope. The molybdenum-99 has a half-life of 66 hours and decays to technetium-99m, which can be extracted from the pot when it is needed for medical use for a period of up to 2 weeks. In Australia the source of molybdenum-99 is ANSTO's research reactor at Lucas Heights.
  4. 4. . Rex Boyd defends the decision to commission a new nuclear reactor. It is claimed by opponents of the nuclear industry that Australia's demand for medical radioisotopes can be met by cyclotrons. The truth is that any number of cyclotrons will never replace Australia's need for a reactor. Australia has two cyclotrons, which use high voltages and electrical fields to accelerate hydrogen atoms through a vacuum chamber. When they collide with a target substance they produce radioactivity. As a general rule, it is more difficult to make a radioisotope in a cyclotron than in a reactor. Cyclotron reactions are less productive and less predictable than nuclear reactions performed in a reactor. The cyclotron produces neutron-deficient radioisotopes whereas the reactor produces neutron-rich radioisotopes. Thus the reactor and the cyclotron complement each other in satisfying society's need for a full range of radioisotopes; rarely one acts as a substitute for the other. A few radioisotopes are exceptions to this rule and can be produced by either facility. One is technetium-99m, currently used in 85% of medical applications. The discovery that technetium-99m can be produced in a cyclotron does not imply that the need for a reactor is disappearing. The half-life of technetium-99m is 6 hours. This means that this radioisotope must be produced and distributed on a daily basis. However, when technetium-99m is produced in a reactor it proceeds through a precursor radioisotope, molybdenum-99, which has a half-life of 66 hours. Thus the weekly production of molybdenum-99 generators can meet all the technetium-99m needs of Australian hospitals. In contrast the cyclotron does not produce molybdenum-99; instead it produces technetium-99m directly. Therefore a network of cyclotrons situated across Australia would be needed to make daily deliveries of technetium-99m to the nation's hospitals. This is one reason why none of the many powerful cyclotrons around the world are used for the manufacture of technetium-99m. Reliance on cyclotrons for our most frequently used medical isotope would have a serious negative impact on the practice of nuclear medicine. The rapid decay of technetium-99m would limit the number of patients treated in any one day and would preclude the use of nuclear medicine techniques in out-of-hours emergency situations when stocks would be exhausted. Appointments would be subject to technetium-99m availability and patient waiting lists would lengthen. Economic factors would also militate against cyclotron-produced technetium-99m. The raw materials for reactor production are cheap (a few dollars per kilogram) and readily available, whereas the starting material for the cyclotron-method is a rare form of molybdenum that must be enriched to high levels of isotopic purity (>99%), is not commercially available and would cost millions of dollars per kilogram. Traces of other molybdenum isotopes in the raw materials can reduce the purity of the technetium-99m. A series of competing nuclear reactions produces undesirable longer-lived technetium radioisotopes, particularly technetium-96, that can accumulate during the day. The level of these impurities may exceed the legal limit and degrade the quality of the scanned image. Other technetium radioisotopes would expose patients to higher radiation doses. Only 0.1% technetium-96 is necessary before radiation exposure of patients is doubled. Hence before cyclotron-produced technetium-99m could be used, certain regulations governing radiopharmaceutical quality would need changing. The cyclotron production of technetium-99m is technically feasible but undesirable for all of these reasons. The frontiers of nuclear medicine now extend beyond the diagnosis of disease with technetium-99m. Other short-lived radioisotopes are being introduced into nuclear medicine with the capability of reducing the pain associated with cancer. Australia must have its own reactor if its community is to have access to these radioisotopes and reap the benefits of the latest advances. Rex Boyd was formerly the director of the $20 million National Medical Cyclotron Project at Sydney's Royal Prince Alfred Hospital.
  5. 5. 5.8 use available evidence to analyse benefits and problems associated with the use of radioactive isotopes in identified industries and medicine Benefits – see earlier table of uses Problems - see below How does cobalt-60 get into the environment? 1. Occasionally, medical or industrial radiation sources are lost or stolen. We call these "orphan sources." They pose a significant risk: • On a number of occasions, people have handled them, not knowing what they were, and have been exposed. • Sometimes sources find their way into municipal landfills, where it is illegal to dispose of them. • Because of their metallic housings, sources 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. The scrap industry uses radiation detectors to screen incoming material. However, sources that are under large loads may be undetected initially. 2. People may ingest cobalt-60 with food and water that has been contaminated, or may inhale it in contaminated dust. The major concern posed by cobalt-60, however, is external exposure to its strong gamma rays. This may occur if you are exposed to an orphaned source, or if you come in contact with waste from a nuclear reactor (though this is very unlikely). 3. All ionizing 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. With any radioisotope, exposure to the radiation, alpha, beta or gamma produced will induce cancers and effect DNA. 4. Any isotope produced in a nuclear reactor, the reactor will always produce radioactive waste that will need to be disposed of (long half lives means waste is producing radioactivity for a long period) and a reactor needs max security from terrorist attack and multiple level safety procedures in place. Cyclotrons do not pose such a risk. 5. Radioisotopes must be transported to industrial sites or hospitals for use. In transit strict OHS rules apply and there is always the risk of accidents or spills releasing isotopes into waterways or human contact. Some hospitals have their own cyclotron on site to avoid the transport issues. eg Royal Prince Alfred Hospital. 6. Tc-99m emits low energy gamma rays and so there is little damage to surrounding tissue. Medical staff must be protected from exposure. The Mo-99 generator is encased in lead to minimise exposure. 7. Reliance on cyclotrons rather than the Lucas Heights reactor for our most frequently used medical isotope Tc-99m would have a serious negative impact on the practice of nuclear medicine. The rapid decay of technetium-99m would limit the number of patients treated in any one day and would preclude the use of nuclear medicine techniques in out-of- hours emergency situations when stocks would be exhausted. Appointments would be subject to technetium-99m availability and patient waiting lists would lengthen. (see Rex Boyd article) 8. Economic factors would also be against cyclotron-produced technetium-99m. The raw materials for reactor production are cheap (a few dollars per kilogram) and readily available, whereas the starting material for the cyclotron- method is a rare form of molybdenum that must be enriched to high levels of isotopic purity (>99%), is not commercially available and would cost millions of dollars per kilogram. 9. The Tc-99m isotope needs to be pure just 0.1% Tc-96 mixed with the sample would double the radiation exposure for patients. 10. People working in the nuclear industry or those who work with radioisotopes must be constantly monitored for exposure to radiation. They wear badges that detect levels of radiation as well as protective clothing to reduce the risk.
  6. 6. 5.8 use available evidence to analyse benefits and problems associated with the use of radioactive isotopes in identified industries and medicine Benefits – see earlier table of uses Problems - see below How does cobalt-60 get into the environment? 1. Occasionally, medical or industrial radiation sources are lost or stolen. We call these "orphan sources." They pose a significant risk: • On a number of occasions, people have handled them, not knowing what they were, and have been exposed. • Sometimes sources find their way into municipal landfills, where it is illegal to dispose of them. • Because of their metallic housings, sources 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. The scrap industry uses radiation detectors to screen incoming material. However, sources that are under large loads may be undetected initially. 2. People may ingest cobalt-60 with food and water that has been contaminated, or may inhale it in contaminated dust. The major concern posed by cobalt-60, however, is external exposure to its strong gamma rays. This may occur if you are exposed to an orphaned source, or if you come in contact with waste from a nuclear reactor (though this is very unlikely). 3. All ionizing 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. With any radioisotope, exposure to the radiation, alpha, beta or gamma produced will induce cancers and effect DNA. 4. Any isotope produced in a nuclear reactor, the reactor will always produce radioactive waste that will need to be disposed of (long half lives means waste is producing radioactivity for a long period) and a reactor needs max security from terrorist attack and multiple level safety procedures in place. Cyclotrons do not pose such a risk. 5. Radioisotopes must be transported to industrial sites or hospitals for use. In transit strict OHS rules apply and there is always the risk of accidents or spills releasing isotopes into waterways or human contact. Some hospitals have their own cyclotron on site to avoid the transport issues. eg Royal Prince Alfred Hospital. 6. Tc-99m emits low energy gamma rays and so there is little damage to surrounding tissue. Medical staff must be protected from exposure. The Mo-99 generator is encased in lead to minimise exposure. 7. Reliance on cyclotrons rather than the Lucas Heights reactor for our most frequently used medical isotope Tc-99m would have a serious negative impact on the practice of nuclear medicine. The rapid decay of technetium-99m would limit the number of patients treated in any one day and would preclude the use of nuclear medicine techniques in out-of- hours emergency situations when stocks would be exhausted. Appointments would be subject to technetium-99m availability and patient waiting lists would lengthen. (see Rex Boyd article) 8. Economic factors would also be against cyclotron-produced technetium-99m. The raw materials for reactor production are cheap (a few dollars per kilogram) and readily available, whereas the starting material for the cyclotron- method is a rare form of molybdenum that must be enriched to high levels of isotopic purity (>99%), is not commercially available and would cost millions of dollars per kilogram. 9. The Tc-99m isotope needs to be pure just 0.1% Tc-96 mixed with the sample would double the radiation exposure for patients. 10. People working in the nuclear industry or those who work with radioisotopes must be constantly monitored for exposure to radiation. They wear badges that detect levels of radiation as well as protective clothing to reduce the risk.

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