A. P. PHYSICS 1 SPANGLER 6/10/2016 A. ATOMIC PHYSICS and QUANTUM EFFECTS 1. PHOTONS and the PHOTOELECTRIC EFFECT 2. WAVE-PARTICLE DUALITY 3. BOHR MODEL and ENERGY LEVELS B. NUCLEAR PHYSICS NUCLEAR REACTIONS IV. M ODERN P HYSICS CONTENT OUTLINE

A. P. PHYSICS 2 SPANGLER 6/10/ NUCLEAR REACTIONS 1.Describe a typical neutron-induced fission, and explain why a chain reaction is possible. 2. Relate the energy released in fission to the decrease in rest mass. OBJECTIVES for the STUDY of NUCLEAR PHYSICS

A. P. PHYSICS 3 SPANGLER 6/10/2016 It is possible to change the structure of nuclei by bombarding them with energetic particles. Such changes are called nuclear reactions. NUCLEAR REACTIONS

A. P. PHYSICS 4 SPANGLER 6/10/2016 PERFORMED BY: Rutherford (father of Nuclear Physics) WHERE: Cambridge WHEN: 1920 ? MATERIALS USED: 1. Naturally occurring radioactive sources 2. Nitrogen gas EXPERIMENTAL PROCEDURE: 1. Bombard nitrogen gas with alpha particles OBSERVATIONS: 1. Protons are produced 2. Unknown produced FIRST MAN MADE NUCLEAR REACTION

A. P. PHYSICS 5 SPANGLER 6/10/2016 Write an equation that says an alpha particle strikes a nitrogen nucleus and produces an unknown product nucleus X and a proton. What is X? Balance Atomic number and Atomic mass, gives Look up in Isotope table: Result ANALYSIS

A. P. PHYSICS 6 SPANGLER 6/10/2016 This reaction starts with two stable isotopes, He and N, and produces two stable, but different, isotopes, H and O. It is possible to change the structure of nuclei by bombarding them with energetic particles. Such changes are called nuclear reactions. Since the time of Rutherford, thousands of nuclear reactions have been observed, particularly following the development of charged-particle accelerators in the 1930s. With today's advanced technology in particle accelerators and particle detectors, it is possible to achieve particle energies of at least 1000 GeV= 1 TeV. These high-energy particles are used to create new particles whose properties are helping to solve the mysteries of the nucleus. CONCLUSION

A. P. PHYSICS 7 SPANGLER 6/10/2016 WHO PERFORMED: Chadwick WHERE: England WHEN: 1932 MATERIALS USED: 1. beryllium target 2. alpha particles EXPERIMENTAL PROCEDURE: Bombard a beryllium target with alpha particles OBSERVATIONS: THE DISCOVERY of the NEUTRON

A. P. PHYSICS 8 SPANGLER 6/10/2016 Write an equation that says an alpha particle strikes a beryllium nucleus and produces an unknown product nucleus (X) and a carbon. What is x in the reaction? Balancing mass numbers and atomic numbers, we see that the unknown particle must be represented as, that is, with a mass of 1 and zero charge. Hence, the particle X is the neutron. CONCLUSIONS: This experiment was the first to provide positive proof of the existence of neutrons. ANALYSIS/CALCULATIONS

A. P. PHYSICS 9 SPANGLER 6/10/2016 WHO PERFORMED: WHERE: WHEN: MATERIALS USED: 1. Uranium target 2. Neutron particles EXPERIMENTAL PROCEDURE: (a) A beam of neutrons is directed at a target of The reaction products are a gamma ray and another isotope. What is the isotope? (b) This isotope is radioactive and emits a beta particle. Write the equation symbolizing this decay and identify the resulting isotope. (c) This isotope is also radioactive and decays by beta emission. What is the end product? (d) What is the significance of these reactions? 3 SYNTHETIC ELEMENTS

A. P. PHYSICS 10 SPANGLER 6/10/2016 (a) Balancing input with output gives: (b) The decay of 239 U by beta emission is: (c) The decay of 239 Np by beta emission gives: ANALYSIS/CALCULATIONS

A. P. PHYSICS 11 SPANGLER 6/10/2016 (d) The interesting feature of these reactions is the fact that uranium is the element with the greatest number of protons, 92, that exists in nature in any appreciable amount. The reactions in parts (a), (b), and (c) do occur occasionally in nature; hence minute traces of neptunium and plutonium are present. In 1940, however, researchers bombarded uranium with neutrons to produce plutonium and neptunium by the steps given above. These two elements were thus the first elements made in the laboratory, and by bombarding them with neutrons and other particles, the list of synthetic elements has been extended to include those up to atomic number 108 (and possibly 109).

A. P. PHYSICS 12 SPANGLER 6/10/2016 We have just examined some nuclear reactions for which mass numbers and atomic numbers must be balanced or conserved in the equations. Q VALUES ENERGY CONSIDERATIONS Exothermic Reactions We shall now consider the energy involved in these reactions, since energy is another important quantity that must be conserved. Let us illustrate this procedure by analyzing the following nuclear reaction:

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A. P. PHYSICS 14 SPANGLER 6/10/2016 The total mass on the left side of the equation is the sum of the mass of 2H ( u) and the mass of 14N ( u), which equals u. Similarly, the mass on the right side of the equation is the sum of the mass of 12C ( u) plus the mass of 4He ( u), for a total of u. The total mass before the reaction is greater than the total mass after the reaction.

A. P. PHYSICS 15 SPANGLER 6/10/2016 This "lost" mass is converted to the kinetic energy of the nuclei present after the reaction. In energy units, u is equivalent to MeV of kinetic energy carried away by the carbon and helium nuclei. The mass difference in this reaction is equal to u u = u. The energy required to balance the equation is called the Q value of the reaction. The Q value for this reaction is MeV.

A. P. PHYSICS 16 SPANGLER 6/10/2016 Nuclear reactions in which there is a release of energy, that is, positive Q values, are said to be exothermic reactions. The energy balance sheet is not complete, however. We must also consider the kinetic energy of the incident particle before the collision. As an example, let us assume that the deuteron has a kinetic energy of 5 MeV. Adding this to our Q value, we find that the carbon and helium nuclei have a total kinetic energy of MeV following the reaction.

A. P. PHYSICS 17 SPANGLER 6/10/2016 Before the reaction, the total mass is the sum of the masses of the alpha particle and the nitrogen nucleus: u u = u. After the reaction, the total mass is the sum of the masses of the oxygen nucleus and the proton: u u = u. Endothermic Reactions Now consider the reaction:

A. P. PHYSICS 18 SPANGLER 6/10/2016 In this case, the total mass after the reaction is greater than the total mass before the reaction. The mass deficits u, is equivalent to an energy deficit of MeV. This deficit is expressed by the negative Q value of the reaction, MeV. Reactions with negative Q values are called endothermic reactions. Such reactions will not take place unless the incoming particle has at least enough kinetic energy to overcome the energy deficit.

A. P. PHYSICS 19 SPANGLER 6/10/2016 NUCLEAR REACTIONS Home Work Problems

A. P. PHYSICS 20 SPANGLER 6/10/ Find the energy released in the following fission reaction: 1 0 n U ----> Ba Kr n 1. Find the energy released in the following fission reaction: 1 0 n U ----> Ba Kr n 1.6x J = 1 MeV

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A. P. PHYSICS 22 SPANGLER 6/10/ Another fission reaction similar to the one in Problem 1 leads to the formation of 141Ba and 92Kr when 235U absorbs a neutron. Write down this reaction. How many neutrons are released?

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A. P. PHYSICS 24 SPANGLER 6/10/ Strontium 90 is a particularly dangerous fission product of 235U because it is radioactive, and it replaces calcium in bones. What other direct fission products would accompany it in the neutron induced fission of 235U? (Note: This reaction may release two, three, or four free neutrons.) 90Sr =54

A. P. PHYSICS 25 SPANGLER 6/10/ =146

A. P. PHYSICS 26 SPANGLER 6/10/ Find the energy released in the following fission reaction: 1 0 n U ----> Sr Xe n

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A. P. PHYSICS 28 SPANGLER 6/10/ If the average energy released in a fission event is 208 MeV, find the total number of fission events required to keep a 100 W light bulb burning for 1.0 h. 5. If the average energy released in a fission event is 208 MeV, find the total number of fission events required to keep a 100 W light bulb burning for 1.0 h.

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A. P. PHYSICS 30 SPANGLER 6/10/ How many grams of 235U must undergo fission to operate a 1000 MW power plant for one day if the conversion efficiency is 30.0%? (Assume 208 MeV released per fission event)

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A. P. PHYSICS 32 SPANGLER 6/10/ An all electric home uses approximately 2000 kWh of electric energy per month. How much 235U would be required to provide this house with its energy needs for one year? (Assume 100% conversion efficiency and 208 MeV released per fission)

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A. P. PHYSICS 34 SPANGLER 6/10/ It has been estimated that the Earth contains 1.0 x 10 9 tons of natural uranium that can be mined economically. Of this total, 0.70% is 235U. If all the world's energy needs (7.0 x J/s) were supplied by 235U fission, how long would this supply last?

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A. P. PHYSICS 36 SPANGLER 6/10/ The first atomic bomb released an energy equivalent to 20 kilotons of TNT. If 1 ton of TNT releases about 4.0 X 10 9 J, how much uranium was lost through fission in this bomb? (Assume 208 MeV released per fission.) 10. The first atomic bomb released an energy equivalent to 20 kilotons of TNT. If 1 ton of TNT releases about 4.0 X 10 9 J, how much uranium was lost through fission in this bomb? (Assume 208 MeV released per fission.)

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A. P. PHYSICS 38 SPANGLER 6/10/ Suppose that the water exerts an average frictional drag of 10 5 N on a nuclear powered ship. How far can the ship travel per kilogram of fuel if the fuel consists of enriched uranium containing 1.7% of the fissionable isotope 235U, and the ship's engine has a efficiency of 20%? ( 208 MeV released per fission event.)

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