Radioisotopes Applications in Nuclear Medicine and Nuclear Energy

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Radioisotopes Applications in Nuclear Medicine and Nuclear Energy By Shireen Abdulrahman

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Transcript of Radioisotopes Applications in Nuclear Medicine and Nuclear Energy

  • 1. ByShireen Abdulrahman

2. IntroductionIn nature there are nearly 300 nuclei, consisting of differentelements and their isotopes.Isotopes are nuclei having the same number of protons butdifferent number of neutrons.Radioactivity is the release of energy and matter that resultsfrom changes in the nucleus of an atom.Radioisotopes A version of a chemical element that has anunstable nucleus and emits radiation during its decay to a stableform. 3. Where Do Radioisotopes Come From?Radioisotopes come from:Nature, such as radon in the air or radium in the soil.Nuclear reactors by bombarding atoms with high-energyneutrons. 4. Radioisotopes radiationThree predominant types of radiation are emitted byradioisotopes: 1. alpha particles 2. beta particles 3. gamma rays. The different types of radiation have different penetrationpowers. 5. Fig: penetration of radiation 6. The half-life of radioisotopes A half-life of a radioactive material is the time it takes one-half of the atoms of the radioisotope to decay by emitting radiation. It can vary from a fraction of a second to millions of years. The half-life of a radioisotope has implications about its use and storage and disposal. 7. Fig: Isotopes half-life decay 8. Radioisotopes in Nuclear EnergyProduction 9. The Basic of Nuclear Energy Nuclear power uses the energy created by controlled nuclearreactions to produce electricity or uncontrolled nuclear reactionto be used in nuclear weapons. 10. Nuclear Fission Nuclear fission is the splitting of an atoms nucleus into parts by capturing a neutron. It is the most commonly used nuclear reaction for power generation. Nuclear fission produces heat (also called an exothermic reaction), and electromagnetic radiation, and it produces large amounts of energy that can be utilized for power. 11. Nuclear Fission Fission produces neutrons which can then be captured by other atoms to continue the reaction (chain reaction) with more neutrons being produce at each step. If too many neutrons are generated, the reaction can get out of control and an explosion can occur. To prevent this from occurring, control rods that absorb the extra neutrons are interspersed with the fuel rods. Uranium-235 is the most commonly used fuel for fission. 12. Fig: Nuclear fission 13. Nuclear Fusion Nuclear fusion is another method to produce nuclear energy. Two light elements, like tritium and deuterium, are forced to fuse and form helium and a neutron. This is the same reaction that fuels the sun and produces the light and heat. Unlike fission, fusion produces less energy, but the components are more abundant and cheaper than uranium. 14. Fig: Nuclear fusion 15. Nuclear weapons Nuclear weapons, like conventional bombs, are designed to cause damage through an explosion, i.e. the release of a large amount of energy in a short period of time. In conventional bombs the explosion is created by a chemical reaction, which involves the rearrangement of atoms to form new molecules. In nuclear weapons the explosion is created by changing the atoms themselves - they are either split or fused to create new atoms. 16. Fig: Nuclear warheads 17. Nuclear MaterialsNuclear materials are the key ingredients in nuclear weapons. They include:1. Fissile materials: which are composed of atoms that can besplit by neutrons in a self-sustaining chain-reaction to releaseenergy, and include plutonium-239 and uranium-235. 18. Nuclear Materials2.Fussionable materials: In which the atoms can be fused inorder to release energy, and include deuterium and tritium.3.Source materials: Which are used to boost nuclear weapons byproviding a source of additional atomic particles for fission.They include tritium, polonium, beryllium, lithium-6 andhelium-3. 19. Uranium When refined, uranium (U) is a silvery white, weakly radioactive metal. Uranium has an atomic number of 92 which means there are 92 protons and 92 electrons in the atomic structure. U-238 has 146 protons in the nucleus, but the number of neutrons can vary from 141 to 146. It is the principle fuel for nuclear reactors, but it also used in the manufacture of nuclear weapons. 20. Uranium Isotopes Natural uranium consists of three major isotopes:1.uranium-238 (99.28% natural abundance).2.uranium-235 (0.71%).3.and uranium-234 (0.0054%). 21. Uranium Isotopes All three are radioactive, emitting alpha particles, with theexception that all three of these isotopes have smallprobabilities of undergoing spontaneous fission, rather thanalpha emission. Table : Half-lives of Uranium Isotopes 22. Enriched uranium Enriched uranium is a kind of uranium in which the percent composition of uranium-235 has been increased through the process of isotope separation. Natural uranium is 99.284% 238U isotope, with 235U only constituting about 0.711% of its weight. 235Uis the only isotope existing in nature (in any appreciable amount) that is fissile with thermal neutrons. 23. Enriched uranium Enriched uranium is a critical component for both civil nuclear power generation and military nuclear weapons. The 238U remaining after enrichment is known as depleted uranium (DU), and is considerably less radioactive than even natural uranium. 24. Uranium enrichment gradesSlightly enriched uranium (SEU)Slightly enriched uranium (SEU) has a 235U concentration of0.9% to 2%. This new grade is being used to replace naturaluranium (NU) fuel in some reactorsLow-enriched uranium (LEU)Low-enriched uranium (LEU) has a lower than 20%concentration of 235U. 25. Uranium enrichment gradesHighly enriched uranium (HEU) Highly enriched uranium (HEU) has a greater than 20% concentration of235U or 233U. The fissile uranium in nuclear weapons usually contains 85% or more of235U known as weapon(s)-grade. HEU is also used in fast neutron reactors, whose cores require about 20% ormore of fissile material, as well as in naval reactors, where it often containsat least 50% 235U, but typically does not exceed 90%. Significant quantities of HEU are used in the production of medicalisotopes, for example molybdenum-99 for technetium-99m generators. 26. First nuclear weapon in historyTwo major types of atomic bombs were developed by the United States during World War II:1. A uranium-based device (codenamed "Little Boy") whosefissile material was highly enriched uranium.2. A plutonium-based device (codenamed "Fat Man") whoseplutonium was derived from uranium-238. 27. First nuclear weapon in historyThe uranium-based Little Boy device became the first nuclearweapon used in war when it was detonated over the Japanesecity of Hiroshima on 6 August 1945.Exploding with a yield equivalent to 12,500 tonnes of TNT, theblast and thermal wave of the bomb destroyed nearly 50,000buildings and killed approximately 75,000 people. 28. Fig: The mushroom cloud over Hiroshima after the dropping of the uranium-based atomic bombnicknamed Little Boy (1945) 29. Uranium Nuclear Fission A team led by Enrico Fermi in 1934 observed that bombarding uranium with neutrons produces the emission of beta rays. Uranium-235 was the first isotope that was found to be fissile. Upon bombardment with slow neutrons, its uranium-235 isotope will most of the time divide into two smaller nuclei, releasing nuclear binding energy in the form of warmth and radiation and more neutrons. 30. Uranium Nuclear Fission If these neutrons are absorbed by other uranium-235 nuclei, a nuclear chain reaction occurs that may be explosive unless the reaction is slowed by a neutron moderator, absorbing them. As little as (7 kg) of uranium-235 can be used to make an atomic bomb. 31. Fig: An induced nuclear fission event involving uranium-235 32. What Happens When People Are Exposedto Radiation? Radiation can affect the body in a number of ways, and the adverse health effects of exposure may not be apparent for many years. These adverse health effects can range from mild effects, such as skin reddening, to serious effects such as cancer and death, depending on the amount of radiation absorbed by the body (the dose), the type of radiation, the route of exposure, and the length of time a person was exposed. Exposure to very large doses of radiation may cause death within a few days or months. Exposure to lower doses of radiation may lead to an increased risk of developing cancer or other adverse health effects later in life. 33. Gulf War syndrome Gulf war syndrome (GWS) or Gulf War illness (GWI) affects veterans and civilians who were near conflicts during or downwind of a chemical weapons depot demolition, after the 1991 Gulf War. Approximately 250,000 of the 697,000 veterans who served in the 1991 Gulf War are afflicted with enduring chronic multi- symptom illness, a condition with serious consequences. Epidemiological evidence is consistent with increased risk of birth defects in the offspring of persons exposed to depleted uranium. 34. Signs and symptomsA wide range of acute and chronic symptoms have included:fatigueloss of muscle controlheadachesdizziness and loss of balancememory problemsmuscle and joint painindigestionskin problemsimmune system problemsbirth defects 35. Depleted uranium exposure effect on gulf warveteransDepleted uranium (DU) was widely used in tank kinetic energy penetratorand autocannon rounds for the first time in the Gulf War.DU is a dense, weakly radioactive metal.After military personnel began reporting unexplained health problems in theaftermath of the Gulf War, questions were raised about the health effect ofexposure to depleted uranium.Depleted uranium aerosol particles, if inhaled, would remain undissolved inthe lung for a great length of time and thus could be detected in urine.Uranyl ion contamination has been found on and around depleted uraniumtargets. 36. Depleted uranium exposure effect on gulf warveteransSeveral studies confirmed the presence of DU in the urineof Gulf War veterans.The use of DU in munitions is controversial because ofquestions about potential long-term health effects.DU has recently been recognized as a neurotoxin.Epidemiological evidence is consistent with increased riskof birth defects in the offspring of persons exposed to DU. 37. Radiation effects from Fukushima Inuclear accidents The radiation effects from the Fukushima I nuclear accidents are the results of release of radioactive isotopes from the Fukushima Nuclear Power Plant after the 2011 Thoku earthquake and tsunami. This occurred due to both deliberate pressure-reducing venting, and through accidental and uncontrolled releases. These conditions resulted in unsafe levels of radioactive contamination in the air, in drinking water, milk and on certain crops in the vicinity of the prefectures closest to the plant. 38. Fig: The explosion at the Fukushima nuclear plant. 39. Isotopes of possible concern The isotope iodine-131 is easily absorbed by the thyroid. Persons exposed to releases of I-131 from any source have a higher risk for developing thyroid cancer or thyroid disease, or both. Iodine-131 has a short half-life at approximately 8 days. Children are more vulnerable to I-131 than adults. Increased risk for thyroid neoplasm remains elevated for at least 40 years after exposure. 40. Isotopes of possible concern Caesium-137 is also a particular threat because it behaves like potassium and is taken-up by the cells throughout the body. Cs-137 can cause acute radiation sickness, and increase the risk for cancer because of exposure to high-energy gamma radiation. Internal exposure to Cs-137, through ingestion or inhalation, allows the radioactive material to be distributed in the soft tissues, especially muscle tissue, exposing these tissues to the beta particles and gamma radiation and increasing cancer risk. 41. Isotopes of possible concern Strontium-90 behaves like calcium, and tends to deposit in bone and blood-forming tissue (bone marrow). 2030% of ingested Sr-90 is absorbed and deposited in the bone. Internal exposure to Sr-90 is linked to bone cancer, cancer of the soft tissue near the bone, and leukemia. 42. Isotopes of possible concern Plutonium is also present in the fuel of the Unit 3 reactor and in spent fuel rods, although there has been no indication that plutonium has been detected outside the reactors. Plutonium-239 is particularly long-lived and toxic with a half- life of 24,000 years, and if it escaped in smoke from a burning reactor and contaminated soil downwind, it would remain hazardous for tens of thousands of years. 43. Radioisotopes in Nuclear Medicine 44. Nuclear medicine Nuclear medicine is a special field of medicine in which radioactive materials are used for: 1. Conducting medical research. 2. generating diagnostic information relating to functioning ofspecific organs. 3. Therapeutic treatment of ailing organs. The radioactive materials used are generally called radionuclides or radioactive tracers, meaning a form of an element that is radioactive (radioisotops). Technetium-99m is a reactor-produced radioisotop that is used in more than 80% of nuclear medicin procedures worldwide. 45. RadionuclidesRadionuclides are powerful tools for diagnosing medicaldisorders for three reasons:1. Many chemical elements tend to concentrate in one part ofthe body or another.2. The radioactive form of an element behaves biologically inexactly the same way that a nonradioactive form of theelement behaves.3. Any radioactive material spontaneously decays, breakingdown into some other form with the emission of radiation.That radiation can be detected by simple, well-knownmeans. 46. Important factors to consider when choosing aradioisotope for medical use1. It must emit gamma rays only:Gamma rays pass through the body, which means they can bedetected with a gamma camera.Alpha particles would not be able to penetrate through the skinso they could not be detected.Gamma rays do not ionize cells inside the body so no damageis caused. Alpha particles and beta particles would ionize cells,which could lead to the formation of cancer cells. 47. Important factors to consider when choosing aradioisotope for medical use 2. It must have a short half-life (typically around a few hours): A short half-life ensures that all the radiation inside the patient leaves the body quickly and does not accumulate. 3. It must be able to be easily administered to the patient. Injections and tablets are used. 48. Technetium Technetium is the chemical element with atomic number 43 and symbol Tc. It is a silvery-gray radioactive metal with an appearance similar to that of platinum. It is commonly obtained as a gray powder. Nearly all technetium is produced synthetically and only minute amounts are found in nature. 49. Technetium Its short-lived gamma ray-emitting nuclear isomer technetium-99mis used in nuclear medicine for a wide variety of diagnostic tests. Technetium-99 is used as a gamma ray-free source of beta particles. Long-lived technetium isotopes produced commercially are by- products of fission of uranium-235 in nuclear reactors and are extracted from nuclear fuel rods. 50. Isotopes 51. Technetium-99m Technetium-99m is a major product of the fission of uranium-235 (235 92U), making it the most common and most readilyavailable Tc isotope. 52. The technetium-99m decay chain A molybdemum-99 nucleus decays into a technetium-99mnucleus by beta emission. After a period of a few hours or sothe technetium-99m emits a gamma ray and changes intotechnetium-99. 53. Technetium -99m Production Technetium below Uranium in the periodic element is actually the only element which does not naturally occur. Technetium -99m is produced by bombarding molybdenum 98Mo with neutrons. The resultant 99Mo decays with a half-life of 66 hours to the metastable state of Tc . This process permits the production of 99mTc for medical purposes. 54. Why is technetium-99m a good tag for medicalimaging?1. its a pure gamma emitter .This means that it doesnt producemore damaging alpha and beta particles and its radioactivitydisappears after a few hours. Most substances arent puregamma emitters.2. The "short" half life of the isotope (in terms of human-activityand metabolism) allows for scanning procedures which collectdata rapidly, but keep total patient radiation exposure low. 55. Common nuclear medicine techniques usingtechnetium-99m Bone scan Myocardial perfusion imaging Cardiac ventriculography Functional brain imaging Blood pool labeling 56. Exposure, contamination, and eliminationRadiation exposure due to diagnostic treatment involvingtechnetium-99m can be kept low.Because technetium-99m has a short half-life and emitsprimarily a gamma ray, its quick decay into the far-lessradioactive technetium-99 results in relatively low totalradiation dose to the patient per unit of initial activity afteradministration, as compared to other radioisotopes.In the form administered in these medical tests (usuallypertechnetate), technetium-99m and technetium-99 areeliminated from the body within a few days.