1.Chapter 2 PROPERTIES OF RADIATION AND RADIOISOTOPESROBERT ESHUN S.L.T Department Accra Polytechnic

2. Electromagnetic radiation is a series of energywaves composed of oscillating electric and magnetic fields traveling at the speed of light through a medium or space. Two broad categories: ionizing and non-ionizingradiations. The energy of the radiation shown on the2spectrum below increases from left to right as the frequency rises. Type of radiation Effects Source 3. 3 4. 4 5. 5 6. Both ionizing and non-ionizing radiation can beharmful to organisms and can result in changes to the natural environment. The different forms of electromagnetic radiation aredistinguished from each other by the amount of energy they can transfer to matter, which depends on their wavelength (frequency).6 7. IONISING RADIATION Radiations with enough high energy to ionize atoms. Ionizing radiation has the power to create charged ionsby displacing electrons in atoms. They have enough energy to remove tightly boundelectrons from atoms, thus creating ions. They can cause chemical changes by breakingchemical bonds. This effect can cause damage to living tissue.7 8. Ionizing radiations include alpha, beta, x-ray andgamma rays. Shorter wavelength u.v. radiation have enoughenergy to break chemical bonds, hence are classified as ionizing. Uses include generation of electric power, killing ofcancerous cells, and in many manufacturing processes. Ionizing radiation can produce a number of 8physiological effects, such as those associated with risk of mutation or cancer. 9. Alpha, beta particles and gamma radiation Type of radiationAlpha particlePenetrating powerMassChargeSpeedStopped by paper or skin4+2SlowBeta particleStopped by thin metalNegligible-1FastGamma ray9SymbolFormulaReduced by many cms of No mass lead or a few metres of concreteNo chargeSpeed lightof 10. Alpha Beta Gamma: Alpha particles - Fast moving helium atoms. They have high energy, typically in the MeV range, but due to their large mass, they are stopped by just a few inches of air, or a piece of paper. Beta - Fast moving electrons. They typically haveenergies in the range of a few hundred keV to several MeV. Since electrons are much lighter than helium atoms, they are able to penetrate further, through several feet of air, or several millimeters of plastic or less of very light metals. Gamma - These are photons, just like light, except of10much higher energy, typically from several keV to several MeV. X-Rays and gamma rays are really the same thing, the difference is how they were produced. Depending on their energy, they can be stopped by a 11. 11 12. NON-IONIZING RADIATION Radiation with enough energy to move atoms in a molecule around or cause them to vibrate, but not enough to remove electrons from them. They have the capacity to change the position ofatoms but not to alter their structure, composition, and properties. Non-ionizing radiations include the spectrum of12ultraviolet (UV), visible light, infrared (IR), microwave (MW), radio frequency (RF), and extremely low frequency (ELF). Lasers commonly operate in the UV, visible, and IR frequencies. 13. Extremely Low Frequency Radiation (ELF)ELF radiation at 60 HZ is produced by power lines, electrical wiring, and electrical equipment. Common sources of intense exposure include ELF induction furnaces and highvoltage power lines. Radiofrequency and Microwave radiationMicrowave radiation is absorbed near the skin, while Radiofrequency (RF) radiation may be absorbed throughout the body. At high intensities both will damage tissue through heating. Sources of RF and MW radiation include radio emitters and cell phones. Infrared Radiation (IR)13The skin and eyes absorb infrared radiation (IR) as heat. Workers normally notice excessive exposure through heat sensation and pain. Sources of IR radiation include furnaces, heat lamps, and IR lasers. 14. Visible Light RadiationThe different visible frequencies of the electromagnetic (EM) spectrum are "seen" by our eyes as different colors. Good lighting is conducive to increased production, and may help prevent incidents related to poor lighting conditions. Excessive visible radiation can damage the eyes and skin. Ultraviolet Radiation (UV)Ultraviolet radiation (UV) has a high photon energy range and is particularly hazardous because there are usually no immediate symptoms of excessive exposure. Sources of UV radiation include the sun, black lights, welding arcs, and UV lasers. Laser hazardsLasers typically emit optical (UV, visible light, IR) radiations and are primarily an eye and skin hazard. Common lasers include CO2 IR laser; helium - neon, neodymium YAG, and ruby visible lasers, and the Nitrogen UV laser. 14 15. Microwave ovens use microwaves to heat food, toastersuse infrared waves to heat; televisions, cell phones, and fm radios use radio waves. Some forms of non-ionizing radiation can damagetissues if we are exposed too much. For instance, too much ultraviolet (UV) light from the sun is known to cause some skin cancers. Apart from the sun, UV radiation are emitted by lightsused in tanning beds, black lights, and lights used to pasteurize fruit juices. Some UV waves have an energy that is high enough to 15cause a structural change within atoms. 16. Interaction of various radiations with matter16 17. Radioactivity This is the spontaneous disintegration of an unstableatomic nucleus and the emission of alpha or beta particles and gamma rays. It also be defined as the spontaneous disintegration ofan unstable nucleus to form a stable nucleus, with the emission of alpha (), beta () or gamma radiation (). All naturally occurring elements with atomic numbersgreater than 83, as well as some isotopes of lighter elements, are radioactive. The emitting nuclide is known as the parent, and the 17particles emitted with the stable nuclide formed are known as daughter. 18. Radioactive decay is the process in which an unstable atomic nucleus loses energy by emitting radiation in the form of particles or electromagnetic waves. There are numerous types of radioactive decay. The general idea:An unstable nucleus releases energy to become more stable 19. Two categories of radioactivity Natural radioactivity: This is the spontaneousdisintegration of naturally occurring radionuclides to form a more stable nuclide with the emission of radiations of alpha, beta and gamma. Artificial radioactivity: This is the spontaneousdisintegration of a nuclide when bombarded with a fast moving thermal neutron to produce a new nuclide with the emission of radiations of alpha, beta and gamma and a large amount heat. 19 20. Derive radioactive decay and half-life equations (solve questions) Discuss the features of radioactive decays (pg. 18 & 19) 20 21. Alpha decay An example is the decay of Radon-222 (Rn-222) asshown in the following equation:21 22. Beta decay A beta particle is essentially an electron thats emittedfrom the nucleus. Iodine-131 (I-131), which is used in the detection and treatment of thyroid cancer, is a beta particle emitter:22 23. Gamma emission Alpha and beta particles have the characteristics ofmatter: They have definite masses, occupy space, and so on. However there is no mass change associated with gamma emission. Gamma radiation is similar to x-rays high energy,short wavelength radiation. Gamma radiation commonly accompanies both alpha and beta emission, but its usually not shown in a balanced nuclear reaction. Some isotopes, such as Cobalt-60 (Co-60), give off 23large amounts of gamma radiation. Co-60 is used in the radiation treatment of cancer. Gamma rays are focused on the tumor to destroy it. 24. Positron emission A positron is essentially an electron that has a positivecharge instead of a negative charge. It is formed when a proton in the nucleus decays intoa neutron and a positively charged electron. The positron is then emitted from the nucleus.24 25. Electron capture This is a rare type of nuclear decay in which an electronfrom the innermost energy level is captured by the nucleus. This electron combines with a proton to form a neutron. The atomic number decreases by one, but the mass number stays the same. The following equation shows the electron capture ofPolonium-204 (Po-204): This creates an isotope of bismuth (Bi-204). The captureof the 1s electron leaves a vacancy in the 1s orbitals. Electrons drop down to fill the vacancy, releasing energy in the X-ray portion of the electromagnetic spectrum. 25 26. Note that for any element: Number of Electrons = Number of Protons = AtomicNumber (Z) Number of Neutrons (n) = Mass Number(A) - AtomicNumber(Z)26 27. Mass defect and Nuclear binding Two forces exist in the nucleus: electrostaticrepulsion and strong force. Electrostatic force is the repulsion between thesimilarly charged protons. Strong force is an attractive short range force. If the electrostatic forces are greater than the strongforce, the nuclide becomes unstable. 27 28. For most atoms the strong forces are greater thanthe electrostatic repulsion. Binding energy is the energy holding protons andneutrons together in an atomic nucleus. This is obtained from the energy equivalence ofmass. The mass of a nucleus is not the same as the sumof the masses of its individual nucleons. 28 29. The mass of an atom is always slightly less thanthe sum of the masses of its individual neutrons, protons and electrons. The difference between the mass of the atom andthe sum of the masses of its component protons, neutrons and electrons is the mass defect (m). The mass defect can be calculated using theequation below.29 30. Neutron = 1.6749286*10-27 kgProton = 1.6726231*10-27 kg Electron = 9.1093897*10-31 kgNeutron = 939.56563 MeV Proton = 938.27231 MeV Electron = 0.51099906 MeV1 amu = 1.6606 x 10-27 kg30 31. Summary/Questions What causes a nucleus to decay? What makes anucleus radioactive? Arrange these emissions from least to greatest penetrability: Gamma, Alpha, Beta. What is the greatest source of exposure to radioactivity in our everyday lives? If I tell you that that the half-life of Fellmanium-250 is 10 days, how much would be left after 30 days if I started with 1600 atoms? 32. NUCLEAR REACTIONS Bombardment of atomic nuclei with energetic particles, resulting in a change in the structure of the nuclei.32 33. Fission reaction Nuclear reaction in which the nucleus of an atomwith a large mass number splits into smaller, lighter nuclei, often producing free neutrons and photons (gamma rays) and releasing a tremendous amount of energy. It is induced by a slow moving neutron. Energy released is in the form of bothelectromagnetic radiation and kinetic energy of resulting fragments. 33 34. It produces millions times the amount of energyobtainable from the same mass of chemical fuels such as petrol. This makes it a very dense source of energy. However, the products of nuclear fission are veryradioactive giving rise to nuclear waste problems.34 35. Nuclear power plant convert energy in the nuclei ofatoms into electrical energy. Nuclear fuels undergo fission when bombarded withneutrons. More neutrons are produced resulting in a self-sustaining chain reaction that releases energy at a controlled rate in a nuclear reactor,... or at a very rapid uncontrolled rate in a nuclear 35bomb booom!!!! 36. uranium nucleusneutronfission fragmentsThe nuclear chain reaction36neutrons 37. 37 38. Reactor charge face 3m thick concrete biological shieldHot gas outSteam out to turbinesReactor coreCold water inHeat exchangerUranium fuel rodsBoron control rods Steel pressure vesselGraphite moderator38Cold gas in 39. Fissionable material - enriched 3% uranium-235and 97% uranium-238 in the form of pellets encased in long tubes known as fuel rods. Control rods - inserted between the fuel rods toabsorb neutrons. They moderate the chain reaction. Pressurised water flowing round fuel rods carriesaway energy released and acts as a coolant. The high pressure is to prevent extremely hot water from boiling. Pressurised water - also slows down the neutrons, 39making them easy to be absorbed. This process is known as thermalization or moderation. 40. The pressurised high temperature water is passedthrough small tubes (primary loop) inside the generator. Feed-water from secondary tubes gets heated asthey flow over the small tubes. This water is returned to the reactor to be heatedagain and again till the temperature is about 2350C and pressurised to about 68 atmospheres. This steam is directed to turn turbines to generate 40electricity. 41. 1kg of uranium U235 can potentially release4.9x1013J of energy! This is enough energy to heat a house, with a5kW heater, 24 hours a day, 7 days a week, 52 weeks a year for over 300 years! It is not quite that simple because its difficult toget ALL the nuclei to split.41 42. Fusion reaction The combination of two light nuclei to form a singleheavier nucleus, with the release of a large amount of energy.42 43. This reaction releases energy which is more than amillion times greater than that obtainable from a typical chemical reaction. The sum of the masses of the product nuclei is lessthan the sum of the masses of the initial fusing nuclei. The mass deficit (lost mass) is converted toenergy, carried away by the fusion products. Most of this energy is released as kinetic energy ofthe resulting particles. 43 44. Large electrostatic repulsion between reactingnuclei since both are positively charged Large initial energy is required to overcomerepulsion and start reaction. When nuclei are close enough, repulsion isovercome by the attractive strong nuclear force, which is stronger at very short distances.44 45. 1 kg of deuterium can potentially release 8.45 x1014 J of energy.45 46. Discuss Peaceful uses of nuke reactions Health hazards from radioactivesubstances. Applications of radioactivity.46