Nuclear Physics

1. Nuclear Physics SPH3U – Unit #3 : Energy

2. Natural Radioactivity • Becquerel accidentally discovered that uranium compounds caused a photographic plate to become fogged. (He was investigating the relationship between x-rays and fluorescence using crystals of uranium potassium sulphate.) • Radioactivity is the spontaneous disintegration of an unstable atomic nucleus and the emission of particles or electromagnetic radiation. • Pierre and Marie Curie investigated uranium ores using chemical separation. They discovered that pitchblende and chalcocite, naturally occurring ores, were highly radioactive due to the presence of plutonium and radium. • All naturally occurring elements with atomic numbers greater than 83, as well as some isotopes of lighter elements, are radioactive. • Based on later work by Rutherford, Soddy, Villard, and others, three different types of radiation were identified. SPH3U – Unit #3: Energy – Topic: Nuclear Physics Created by: Mr. D. Langlois - GECDSB

3. The Alpha, Beta, Gammas of Radiation • Alpha particles are helium nuclei, containing two protons and two neutrons. They are deflected slightly in an electric or magnetic field. Their penetrating power is very low, being stoppable by a thin sheet of aluminum or paper. • Beta particles are electrons capable of traveling at speeds approaching the speed of light. Their low mass allows them to be deflected greatly in an electric or magnetic field, in the opposite direction as the deflection of alpha particles. Their high speed gives them greater penetrating power than alpha particles. Some beta particles can penetrate several centimetres of aluminum. • Alpha particle emissions and beta particle emissions change the composition of the nucleus. • Gamma rays are high energy electromagnetic radiation with short wavelengths. Gamma rays, unlike alpha and beta particles, do not change the composition of the nuclide. They have the highest penetrating power, being able to penetrate at least 30 centimetres of lead. SPH3U – Unit #3: Energy – Topic: Nuclear Physics Created by: Mr. D. Langlois - GECDSB

4. Testing Penetrating Strength • Radioactive particles video SPH3U – Unit #3: Energy – Topic: Nuclear Physics Created by: Mr. D. Langlois - GECDSB

5. Characteristics of Radioactive Materials • All radioactive nuclides have the following common characteristics: • Their radiations affect the emulsion of photographic film, ionize surrounding air molecules, make certain compounds fluoresce, and have certain special biological effects. • They undergo radioactive decay. • Radioactivity is found in naturally occurring sources and in artificially produced ones. • People are constantly being exposed to radiation from a variety of natural and human-created sources. Exposure should be minimized, but it can never be reduced to zero. SPH3U – Unit #3: Energy – Topic: Nuclear Physics Created by: Mr. D. Langlois - GECDSB

6. Nuclear Notation • Some commonly used symbols for subatomic particles are: • neutron • proton • electron (beta particle) • positron (A positron is a particle much the same as an electron, but with a positive charge. It is an example of "antimatter".) • alpha particle • gamma ray (photon) SPH3U – Unit #3: Energy – Topic: Nuclear Physics Created by: Mr. D. Langlois - GECDSB

7. Detecting Radiation • Radioactivity can not be detected with our senses. Special detectors are needed. Because it can not be detected by human senses it is particularly dangerous; one may unknowingly be exposed to it for prolonged periods of time. Radiation has an effect on tissue and on genetic material. • Several devices have been developed to detect radioactivity, with the earliest being an unexposed photographic plate placed in the vicinity of a source being detected. Other devices include a Wilson cloud chamber, electroscopes, ionizing chambers, the Geiger-Muller tube, liquid and electronic bubble chambers, scintillation detectors (spinthariscope), and solid state semiconductor devices. • Dosimetry is the measurement of radiation and the study of its effects on living organisms. SPH3U – Unit #3: Energy – Topic: Nuclear Physics Created by: Mr. D. Langlois - GECDSB

8. Test Yourself • Define the following terms: radioactivity, isotopes, alpha particles, beta particles, gamma rays • State how radioactivity was discovered. • Develop a generalization based on atomic number regarding some radioactive elements. • State the number of different types of radiation found in nature. • Identify the composition of alpha particles, beta particles, and gamma rays. • Compare the penetrating power, speed, potential danger, and other important characteristics of alpha particles, beta particles, and gamma rays. • Identify common characteristics of all radioactive nuclides. • Suggest some important implications arising from the fact that radioactivity can not be detected by human senses. • Identify one device that can be used to detect radioactivity. SPH3U – Unit #3: Energy – Topic: Nuclear Physics Created by: Mr. D. Langlois - GECDSB

9. Nuclear Fission • A neutron can be captured by the nucleus of some heavy atoms. The nucleus then becomes unstable and splits. Other neutrons are released when the nucleus splits. • Fission is the term used to describe the splitting of a heavy nucleus into two or more smaller nuclei. • Slow moving neutrons are more easily captured by the nucleus. A moderator is a medium which causes neutrons to travel more slowly. • Graphite, heavy water, and beryllium are all excellent moderators, capable of slowing neutrons without absorbing them. • The neutrons liberated by fission travel very quickly unless moderated. • A very large amount of energy is released when an atom undergoes fission. ( 200 MeV or Mega electron volts – a unit of energy commonly used in subatomic physics. 1.60x10^-19 J = 1 eV) • In a typical fission reaction, the energy released is distributed as follows: 170 MeV of kinetic energy of fission fragments, 5 MeV of kinetic energy of neutrons, 15 MeV of energy beta particles and gamma rays, and 10 MeV as energy of antineutrinos. SPH3U – Unit #3: Energy – Topic: Nuclear Physics Created by: Mr. D. Langlois - GECDSB

10. The Mass-Energy Interface • Mass is not conserved in a nuclear reaction. The products formed during nuclear fission have a slightly lower mass, due to the nuclear mass defect. This nuclear mass defect can be used to determine the nuclear binding energy which held the heavier nucleus together and was released when fission occurred. • The energy released by a fission can be calculated by finding the difference between the mass of the parent atom and neutron, and the masses of the daughter atoms and emitted neutrons, and converting this mass "loss" into energy using E = mc^2, where m is the change in mass from the parent to daughter atoms, and c is the speed of light (3.0x10^8 m/s) • Neutrons released when an atom undergoes fission are capable of causing other nuclei to undergo fission, if the neutrons are slowed down by a moderator. • A sustained fission reaction caused in this way is called a chain reaction. SPH3U – Unit #3: Energy – Topic: Nuclear Physics Created by: Mr. D. Langlois - GECDSB

11. Fission Videos SPH3U – Unit #3: Energy – Topic: Nuclear Physics Created by: Mr. D. Langlois - GECDSB

12. E=mc^2 • It is believed that the famous equation E=mc^2 applies to most processes, although the changes are usually far too small to be measured. • For example, the heat of combustion of coal is approximately 3.2x10^7 J/kg. If 1.0 kg of coal is burned, what change would the release of energy in light and warmth make in the mass of coal compared with the mass of the products of combustion? We can see this is a negligable amount of mass which is not detectable with even the most sensitive electronic balance. SPH3U – Unit #3: Energy – Topic: Nuclear Physics Created by: Mr. D. Langlois - GECDSB

13. Examples • Calculate the energy released when 0.250kg of Uranium splits into two smaller atoms which each have a mass of 0.121kg. [ANS:7.2x10^14J] • The total energy consumption of Canada is about 9.80x10^18 J. How much mass would have to be totally converted into energy to meet this need. [ANS: 1.09x10^2kg] • Calculate the energy of a proton in electron volts. The mass of a proton is 1.67x10^-27kg. [ANS: 939 MeV] SPH3U – Unit #3: Energy – Topic: Nuclear Physics Created by: Mr. D. Langlois - GECDSB

14. Nuclear Reactors • Natural uranium ore contains about 0.7% uranium-235. To increase the likelihood of sustaining a chain reaction for uranium, the fissionable isotope of uranium must be increased in its relative proportion through enrichment. • A nuclear reactor produces a sustained chain reaction at a controlled rate. The heat energy produced by the reaction is used to drive turbines, generating electricity. • Control rods, made of materials such as cadmium which absorb neutrons, are used to control the rate of a chain reaction in a nuclear reactor. • A critical mass of fissionable material is the minimum mass that will produce a nuclear explosion. To produce a sustainable nuclear chain reaction requires more material than the critical mass. SPH3U – Unit #3: Energy – Topic: Nuclear Physics Created by: Mr. D. Langlois - GECDSB

15. The CANDU Reactor • The CANDU reactor (Canadian deuterium uranium) uses uranium, bundled in the form of uranium oxide fuel pellets, to produce electricity. (A comparison between CANDU reactors and other types of reactors would be an interesting optional extension topic.) • Saskatchewan has abundant deposits of uranium ore which is refined for use in nuclear reactors. • The refined uranium oxide fuel pellets are stacked into cylindrical rods. The rods are arranged into a fuel bundle which is then ready to be placed in special pressure tubes inside the reactor. • The reactor vessel is called the calandria. SPH3U – Unit #3: Energy – Topic: Nuclear Physics Created by: Mr. D. Langlois - GECDSB

16. What if…? • Nuclear reactors can not explode like a nuclear bomb. Even under a worst-case scenario, with a core meltdown, a critical mass of fuel would not be present and the fuel would burn into the ground. (This, of course, would lead to very serious consequences, including possible loss of life and environmental damage.) SPH3U – Unit #3: Energy – Topic: Nuclear Physics Created by: Mr. D. Langlois - GECDSB

17. Fuel of a Reactor • Refueling can be done by removing fuel bundles from the pressure tubes and replacing them with new bundles. In a CANDU reactor this can be done without having to shut the reactor down. • Heavy water is used as the moderator in a CANDU reactor. Heavy water contains deuterium, an isotope of hydrogen having one neutron in the nucleus. Heavy water also transfers heat from the fuel into a heat exchanger which heats ordinary water to produce steam. SPH3U – Unit #3: Energy – Topic: Nuclear Physics Created by: Mr. D. Langlois - GECDSB

18. The Process • The steam produced is used to turn turbines which are connected to electric generators. • Condensers change the steam back into water so it can be cycled back to the steam generator. • Some experts believe that the design of the CANDU reactor makes them safer than other types of nuclear reactors. • If excess heat builds up in the calandria, the heavy water can be drained out. This causes the chain reaction to stop, because the moderator is no longer present. SPH3U – Unit #3: Energy – Topic: Nuclear Physics Created by: Mr. D. Langlois - GECDSB

19. Pro’s and Cons • Supporters of the use of nuclear energy feel that it is a safe and effective way to produce energy. With the demand for energy increasing, and the problems associated with burning fossil fuels, such as acid precipitation and the greenhouse effect, they regard the use of nuclear energy as being necessary. • Nuclear energy avoids some of the problems of generating hydro-electric power. Flooding land to build dams creates environmental and social problems. • The use of nuclear energy may avoid the need for long transmission lines. Nuclear plants can be built in relatively close proximity to where the power is needed. SPH3U – Unit #3: Energy – Topic: Nuclear Physics Created by: Mr. D. Langlois - GECDSB

20. Pro’s and Cons • Nuclear energy produces very small amounts of waste by volume. The radioactive materials can be concentrated for storage and monitoring in one place. Poisonous metals (such as arsenic, lead, and mercury), toxic gases, carbon dioxide, and fly ash are not released into the atmosphere. • Critics of the use of nuclear energy cite various problems with its use. The opposition to the use of nuclear energy has grown so strong in recent years, that some reactors have been shut down. Other reactors scheduled for development have been delayed or were never completed because of the social and political pressure exerted by the antinuclear lobby. The debate continues. • The Chernobyl nuclear accident lead to a justifiable scepticism about any claims of the safety of nuclear reactors, particularly if those claims come from spokespersons of the industry, who often cite the strict controls and regulations faced by the industry. SPH3U – Unit #3: Energy – Topic: Nuclear Physics Created by: Mr. D. Langlois - GECDSB

21. Pro’s and Cons • CANDU reactors need to be built near a large body of water. Fresh water is circulated through the condensers. Excess heat is returned to the source. Raising the temperature reduces the oxygen content of the water, creating an environmental stress on many kinds of living organisms. The heated water does, however, offer some possibilities for commercial aquaculture, allowing for warm-water species to be harvested in colder regions. The excess heat can also be used for commercial greenhouses or other applications. Air cooling is possible. • Critics also suggest that mining safety is an issue with the use of nuclear energy. The ore is slightly radioactive. Radon gas is often present at the mine site. The disposed tailings contain trace amounts of uranium. Unless they can be disposed of properly, they can cause ground water contamination and environmental damage to the land on which they are dumped. SPH3U – Unit #3: Energy – Topic: Nuclear Physics Created by: Mr. D. Langlois - GECDSB

22. Nuclear Fuel Cycle • The entire cycle, from mining the fuel to its eventual disposal after use, is called the nuclear fuel cycle. • Used nuclear fuel is both hot and radioactive. It is stored under water in large cooling pools for up to two years after use, until it cools. Some of the used fuel will still remain radioactive for up to several thousand years. This concerns many people. • The storage of used fuel is a contentious issue for those concerned about the protection of the environment. No ideal solution has yet been developed to dispose the waste. Current proposals for waste management merely offer temporary storage solutions until better methods become available. SPH3U – Unit #3: Energy – Topic: Nuclear Physics Created by: Mr. D. Langlois - GECDSB

23. Nuclear Fuel Cycle • Storage of waste in underground salt mines offers one possible solution. Formations in the Canadian Shield offer other possibilities. The area being considered as a storage site must be dry and relatively free of earthquake and volcanic activity. • Decommissioning of nuclear reactors, once they have completed their useful service, is another issue frequently raised by opponents to the use of nuclear energy. • One of the waste materials from a nuclear reactor is plutonium. It is known to cause cancer in extremely small quantities. It is also used to make nuclear weapons. Some argue against the use of nuclear reactors because they provide a country with the potential to build a nuclear weapons arsenal. (An interesting anecdote is that of the development of India's first atomic bomb, which occurred partially as a result of their having purchased the rights to the CANDU technology from Canada. This occurred in spite of India having been under a contractual obligation not to exploit CANDU reactor technology for anything other than peaceful uses.) SPH3U – Unit #3: Energy – Topic: Nuclear Physics Created by: Mr. D. Langlois - GECDSB

24. How a Nuclear Power Plant Works • Nuclear Energy Plant Video SPH3U – Unit #3: Energy – Topic: Nuclear Physics Created by: Mr. D. Langlois - GECDSB

25. Nuclear Weapons • An atomic bomb explodes when two or more sub-critical masses of fissionable material are brought together very rapidly. Chemical explosives are used to implode the sub-critical masses together to form a mass larger than the critical mass. • An atomic bomb produces devastating destruction. Its explosive force is measured in terms of the comparable number of megatons of conventional explosives that would be needed to produce similar results. • Nuclear weapons produce radioactive contamination of the environment. For this and other reasons many countries have banned atmospheric testing of these weapons. SPH3U – Unit #3: Energy – Topic: Nuclear Physics Created by: Mr. D. Langlois - GECDSB

26. History of the Atomic Bomb • The first atomic bombs, developed and tested by the United States during the Manhattan Project in World War II, were dropped on the Japanese cities of Hiroshima and Nagasaki in 1945. Over 110 000 people were killed and many others suffered from the effects of the explosions for years afterwards. Japan surrendered shortly after the atomic bombs were dropped, bringing the war to an end. • Leo Szilard, one of the developers of the atomic bomb, recommended that it be tested before an international audience of observers prior to being used, offering the Japanese a chance to surrender beforehand. Whether or not the atomic bomb should have been used is an issue worthy of debate. SPH3U – Unit #3: Energy – Topic: Nuclear Physics Created by: Mr. D. Langlois - GECDSB

27. Today’s Nuclear Weapons • Today the nuclear arsenals of the superpowers contain such vast supplies of nuclear weapons that, according to one scenario, if a large proportion of them were deployed simultaneously, it would render the planet virtually uninhabitable by humans. Contemporary societal reactions to this issue are growing. • Should scientists ultimately help bring about an understanding that nuclear weapons are immoral? Do such weapons threaten the existence of all forms of life on Earth? These are questions worth pondering. • Should a scientifically literate society help to reduce the potential threat of nuclear war? Can nuclear weapons be thought of as a "deterrent" if their destructive capabilities could be so severe that it may be unreasonable to consider their use for solving international conflict? SPH3U – Unit #3: Energy – Topic: Nuclear Physics Created by: Mr. D. Langlois - GECDSB

28. Test Yourself • Define the following terms: fission, moderator, nuclear mass defect, chain reaction, enrichment, control rods, nuclear reactor, critical mass. • Describe what happens during a fission reaction. • Give an example of a substance which can act as a good moderator. • Explain how the neutrons released during a fission reaction can help to sustain the reaction. • Describe how a nuclear reactor works. • Identify the type of fuel used in a nuclear reactor. • Outline the nuclear fuel cycle, from the initial mining of raw materials to the final storage of waste material. • Explain why a nuclear explosion is not possible in a nuclear reactor. • Identify some of the main features of the CANDU nuclear reactor. • Explain the purpose of using heavy water in CANDU reactors. SPH3U – Unit #3: Energy – Topic: Nuclear Physics Created by: Mr. D. Langlois - GECDSB

29. Test Yourself • State some of the facts that supporters of the use of nuclear energy use to substantiate their position. • State some of the concerns that critics raise regarding the use of nuclear energy. • Suggest what concerns regarding the environment emerge as a result of the use of nuclear energy. • Suggest how environmental concerns regarding the use of non-nuclear methods of electrical generation might be alleviated with the use of nuclear energy. • Using a solid knowledge base of all of the previous outcomes, develop a position which either supports or rejects the use of nuclear energy for peaceful purposes. • Defend a position which either supports or rejects the use of nuclear energy for peaceful purposes. • Defend a position which either supports or rejects the use of nuclear energy for military purposes. SPH3U – Unit #3: Energy – Topic: Nuclear Physics Created by: Mr. D. Langlois - GECDSB

30. Atomic Theory • Rutherford's gold foil experiment, performed in conjunction with Geiger and Marsden, provided evidence for the nucleus due to the scattering of alpha particles. The repulsion of some alpha particles suggested that the nucleus is positively charged, containing protons within the nucleus of the atom. • The atomic number describes the number of protons in the nucleus. For a neutral atom this is also the number of electrons outside the nucleus. • Subtracting the atomic number from the atomic mass number gives the number of neutrons in the nucleus. SPH3U – Unit #3: Energy – Topic: Nuclear Physics Created by: Mr. D. Langlois - GECDSB

31. Atomic Theory • Isotopes are atoms of the same element (i.e., they have the same number of protons, or the same atomic number) which have a different number of neutrons in the nucleus. Isotopes of an element have similar chemical properties. • Radioactive isotopes are called radioisotopes. • Most of the elements in the periodic table have several isotopes, found in varying proportions for any given element. • The average atomic mass of an element takes into account the relative proportions of its isotopes found in nature. SPH3U – Unit #3: Energy – Topic: Nuclear Physics Created by: Mr. D. Langlois - GECDSB

32. Binding Force • A nuclear binding force holds the nucleus of the atom together. The nuclear mass defect, a slightly lower mass of the nucleus compared to the sum of the masses of its constituent matter, is due to the nuclear binding energy holding the nucleus together. • The mass defect can be used to calculate the nuclear binding energy, with E = mc^2. • The average binding energy per nucleon is a measure of nuclear stability. The higher the average binding energy, the more stable the nucleus. SPH3U – Unit #3: Energy – Topic: Nuclear Physics Created by: Mr. D. Langlois - GECDSB

33. Test Yourself • Define the following terms: atomic number, isotope, radioisotopes, nuclear binding force, average binding energy, nuclear mass defect, nuclear binding energy. • Use the atomic number of an element to determine the number of protons in a nucleus. • Infer the number of electrons in a neutral atom from the atomic number of an element. • Use the atomic mass number and the atomic number to determine the number of neutrons in the nucleus of an atom. • Recognize that isotopes of an element have similar chemical properties, but different physical properties. • Give an example of an element which contains isotopes and show how those isotopes differ from each another. SPH3U – Unit #3: Energy – Topic: Nuclear Physics Created by: Mr. D. Langlois - GECDSB

34. Half-Life & Radioactive Decay • Transmutation describes a process by which the nucleus of a radioactive atom undergoes decay into an atom with a different number of protons, until such time as a stable nucleus is produced. • An alpha particle (i.e., a helium nucleus) is released during alpha decay of a radioactive substance. An element with a lower mass is formed. • Ex: SPH3U – Unit #3: Energy – Topic: Nuclear Physics Created by: Mr. D. Langlois - GECDSB

35. Criteria for Alpha Decay • In general, if X is the parent nucleus and Y is the daughter nucleus: • For alpha decay: • Alpha decay can only occur if Mx > My + MHe. The atomic masses of He and Y are less than the mass of the parent atom, X. This "lost" mass is converted into energy (E = mc2) which appears as kinetic energy of the alpha particle. SPH3U – Unit #3: Energy – Topic: Nuclear Physics Created by: Mr. D. Langlois - GECDSB

36. Alpha Decay • Recall that alpha particles have the ability to penetrate 5cm of air and to penetrate a few sheets of paper. They must therefore possess some kinetic energy. So where did the energy come from? • The protons within the nucleus repel one another through the electromagnetic force. A stable nucleus must therefore be held together by a force that is – at least over short distances stronger than the electric force. This force is called the STRONG NUCLEAR FORCE. • Since the strong nuclear force is attractive, work must be done to break the nucleus apart. SPH3U – Unit #3: Energy – Topic: Nuclear Physics Created by: Mr. D. Langlois - GECDSB

37. Example • An unstable polonium atom spontaneously emits an alpha particle and trasmutes into an atom of some other element. Show the process, including the new element, in standard nuclear-reaction notation. SPH3U – Unit #3: Energy – Topic: Nuclear Physics Created by: Mr. D. Langlois - GECDSB

38. Converting Mass Units to Energy Units • Recall that E=mc^2 relates the mass of an object in kilograms to the energy of the object in joules. • If the mass of an object is given in atomic mass units (u), then the following conversion factor can be used: • 1 u = 931.4 MeV/c^2 • Studies have shown that the mass of an atomic nucleus is always less than the sum of the masses of its constituent neutrons and protons. The energy equivalent of the mass difference is the Binding Energy, or positive work that would have to be done to break a nucleus apart. SPH3U – Unit #3: Energy – Topic: Nuclear Physics Created by: Mr. D. Langlois - GECDSB

39. Example • Calculate the total kinetic energy, in electron volts, of the daughter particles released when Uranium 236 undergoes alpha decay. • Given: SPH3U – Unit #3: Energy – Topic: Nuclear Physics Created by: Mr. D. Langlois - GECDSB

40. Beta Decay • Beta decay (beta negative decay) occurs when a beta (negative) particle is released from the nucleus (i.e., electron). • i.e. In the above example thorium-234 releases a beta particle, forming protactinium-234. Mass is also not conserved in beta decay. Nucleon number is conserved. In beta decay, the beta particle released originated in the nucleus of the atom, not in the electron orbital. A neutron is lost, and in its place a proton and an electron are formed. SPH3U – Unit #3: Energy – Topic: Nuclear Physics Created by: Mr. D. Langlois - GECDSB

41. Beta Decay • Although to understand Beta decay we are assuming that a neutron is the combination of a proton and electron, this model is incorrect for several reasons. • A better model requires the understanding of the elementary particles called quarks, which is not needed at this time. SPH3U – Unit #3: Energy – Topic: Nuclear Physics Created by: Mr. D. Langlois - GECDSB

42. Criteria for Beta Decay • For beta decay: • (v is a neutrino) • (Actually an antineutrino is produced for beta emission.) • My < Mx The mass deficit appears as kinetic energy of the electron (and energy of the neutrino). • A neutrino was "invented" to maintain conservation of energy, linear momentum, and angular momentum in beta decay. It has no mass, no charge, and virtually no interaction with matter. It travels at the speed of light and carries off energy and momentum. SPH3U – Unit #3: Energy – Topic: Nuclear Physics Created by: Mr. D. Langlois - GECDSB

43. Example • An atom of Sodium-24 can transmute into an atom of some other element by emitting a beta particle. Represent this reaction in symbols and identify the daughter element. SPH3U – Unit #3: Energy – Topic: Nuclear Physics Created by: Mr. D. Langlois - GECDSB

44. Example • Calculate the energy released in the previous example. • Given: SPH3U – Unit #3: Energy – Topic: Nuclear Physics Created by: Mr. D. Langlois - GECDSB

45. The Weak Nuclear Force • Recall that alpha decay was explained with reference to the strong nuclear force, which binds nucleons together. • It is not the same force which gives an explanation of beta decay. The force which must be overcome for beta decay to occur is the Weak Nuclear Force. SPH3U – Unit #3: Energy – Topic: Nuclear Physics Created by: Mr. D. Langlois - GECDSB

46. Gamma Decay • Gamma decay is the release of excess stored energy from the nucleus. No transmutation occurs. However, gamma decay often accompanies alpha and beta negative decay in a disintegration series. Gamma decay results in the production of photons that have zero mass and no electric charge. • Gamma decay occurs when an excited nucleus (excited by photon or particle bombardment, or it may be a decay product in an excited state) returns to the ground state. An excited nucleus is heavier than the ground state, by a mass equal to the mass/energy equivalent of the energy of the emitted gamma ray. (The asterisk indicates an "excited" nucleus.) SPH3U – Unit #3: Energy – Topic: Nuclear Physics Created by: Mr. D. Langlois - GECDSB

47. Gamma Rays • In reality Gamma rays are very similar to X-rays. However, they are typically of a higher frequency and thus higher energy than X-rays, although there is some overlap in their frequency ranges. • Physicists distinguish between the 2 based on how they’re produced: X-rays occur when high energy electrons interact with matter, while Gamma Rays are produced within the nucleus. SPH3U – Unit #3: Energy – Topic: Nuclear Physics Created by: Mr. D. Langlois - GECDSB

48. Example • Give the values of x & y in each of the following equations: SPH3U – Unit #3: Energy – Topic: Nuclear Physics Created by: Mr. D. Langlois - GECDSB

49. Decay Series • A series of nuclear transmutations occurs until a stable nucleus results. The series of steps in the transmutations is called a disintegration series (or decay series). • Nuclide charts, with atomic number plotted against neutron number, are used in nuclear physics to illustrate a disintegration series. SPH3U – Unit #3: Energy – Topic: Nuclear Physics Created by: Mr. D. Langlois - GECDSB

50. Background Radiation • Background radiation comes from a variety of radioactive sources. Cosmic rays penetrating the Earth's atmosphere from outer space usually account for less than 25% of background radiation (but this depends on altitude). • Minute quantities of naturally occurring radioactive sources in the surroundings (e.g., soil, air, drinking water, building materials, food, etc.) also contribute to background radiation. SPH3U – Unit #3: Energy – Topic: Nuclear Physics Created by: Mr. D. Langlois - GECDSB