Nuclear Energy Nuclear Structure and Radioactivity I. Review - Periodic Table A. Atomic Number: The number of protons in the nucleus of an atom B. Atomic Mass: The sum of the mass of protons, neutrons and electrons in the atom # of neutrons = atomic mass - atomic number 1
II. Review - Atomic Structure Recognize Me? A. Atomic Structure: Atoms contain protons, neutrons and electrons B. Isotopes: Why are atomic masses decimals? The number of neutrons in an atom is not always the same! 2 atoms of the same element can have a different number of neutrons a weighted average of all neutron versions of a given element = an atomic mass with a decimal III. Radioactivity A. Definition: the emission of radiation due to the breakdown of atomic nuclei B. Description of Process: large atoms are unstable as a result their nuclei decay mass and energy is lost during nuclear decay new, lighter atoms are formed unstable atoms continue to decay until they become stable 2
IV. Radiation A. Definition: Energy and/or mass that is emitted in the form of rays, waves or particles B. Types of Radiation 1. Alpha (a) Particle : Equivalent of nucleus of a helium atom; Charge (+2); Mass of 4 Decay Process: Alpha decay occurs because the nucleus has too many protons which causes excessive repulsion. An alpha particle is emitted to reduce this. Impact on decaying atom: The atomic # of the decaying atom decreases by 2 and the mass decreases by 4 Symbol 4 2 a 2. Beta (b) Particle : High speed electron Charge (-1); No measurable mass Decay Process: Beta decay occurs when the neutron to proton ratio is too great and causes instability. A beta particle is emitted, converting a neutron into a proton. Impact on decaying atom: The atomic # of the decaying atom increases by 1 and the mass does not change Symbol 0-1 b 3
3. Gamma ( g ) Ray : High energy photon (wave) No charge; No measurable mass Decay Process: Gamma decay occurs because the nucleus is at too high an energy. A gamma ray is emitted as the nucleus falls to a lower energy state. Impact on decaying atom: The atomic number and mass of the decaying atom do not change Symbol 0 0 g V. Energy Generated From Nuclear Fission A. Definition: The splitting of large atomic nuclei into smaller fragments B. Description of Process: A large atom is struck by a single neutron Fission products include smaller atoms, neutrons and heat energy Uranium-235 is the most common isotope used to generate useable nuclear energy in power plants 4
C. Energy Released from Nuclear Fission Fission events release about 200 million electronvolts of energy for each fission event. Burning coal or TNT releases at most a few electronvolts per event D. Source of Energy The mass of protons and neutrons in the immediate system before a nuclear reaction is greater than after the reaction Mass emitted as radiation is transformed into kinetic energy according to Einstein s famous equation E=mc 2 The speed of light (c) is 300,000 kilometers per second, so a very small amount of mass produces LOTS of energy! [186,000 miles per second] VI. Energy Generated From Nuclear Fusion A. Definition: The combining of small atomic nuclei to form larger ones B. Description of Process: The mass of the combination is less than the sum of the masses of the individual nuclei. Emitted mass is converted into energy! Takes place continuously in the sun and stars (H is fused creating He) For energy production on earth, the nuclei of two isotopes of hydrogen are used: Deuterium and Tritium C. Energy Released from Nuclear Fusion: 10 grams of Deuterium which can be extracted from 500 liters of water could produce enough fuel for the lifetime electricity needs of an average person in an industrialized country. 5
Nuclear Energy Summary Diagram VII. Pros and Cons of Nuclear Power Plants A. Advantages: Fuels are plentiful and inexpensive If shielded properly, it is inherently safe since any malfunction results in a rapid shutdown No atmospheric pollution leading to acid rain or global warming Small amounts of mass yield high amounts of energy B. Disadvantages: Nuclear power plants are expensive to build and maintain No technology for the safe, permanent containment of radioactive wastes has been developed and tested Exposure to radiation can cause major health issues 6
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