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Learn about natural radioactivity, nuclear equations, alpha decay, decay series, and how to balance nuclear equations for various isotopes. Understand the changes in mass and atomic numbers during decay processes.
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Natural Radioactivity – Unstable Nuclei Emit Radiation • Spontaneous nuclear change to attain good n/p ratio. • Form a new kind of atom. • Each isotope or nuclide decays in a certain manner to get a better n/p ratio. The decay mode is named for the particle emitted. See Table N.
Nuclear Equations • Describe the decay process. • reactant or starting side (left) product or ending side (right). • separates two sides
Nuclear Equations - tasks • Have to identify type (out of 4) • Have to balance to find 1 unknown term.
Natural Transmutation – I.D. • 1 term on the reactant side – starting isotope. • 2 terms on the product side – ending isotope and emitted particle. • Type of particle emitted is characteristic of the isotope – look up particle in Table N.
Nuclear Equations • Use conservation of atomic number & conservation of mass number to balance them. • Mass number = left superscript. • Atomic Number = left subscript.
Writing Equations • Write the equation for the decay of Thorium-232. • Use Table N to find the decay mode: • Write the initial equation: 232Th 4He + X 90 2 Have to figure out what element it turned into.
Alpha decay, Th-232 232Th 4He + YX 90 2 Z
Alpha decay, Th-232 so Y = 228 232 = 4 + Y 232Th 4He + X Y Z 90 2 Conservation of Mass Number: The sum of the mass numbers on the left side must equal the sum of the mass numbers on the right side.
Alpha decay, Th-232 232Th 4He + 228X 90 2 Z 90 = 2 + Z so Z = 88 Conservation of Atomic Number: The sum of the atomic numbers on the left side must equal the sum of the atomic numbers on the right side.
Alpha decay, Th-232 232Th 4He + 228X 90 2 88 X = Ra Use the P.T. to find X: 232Th 4He + 228Ra 90 2 88
Nuclear Equations • If there is only 1 unknown term you can figure out what it is. • Doesn’t matter which one isn’t known. • Don’t forget – you can look up the decay mode in Table N. Decay mode means what particle is emitted.
Write an equation for the decay of Am-241 241 = 4 + Y so Y = 237 241 Am 4He + YX Z 95 2 so Z = 93 95 = 2 + Z X = Np What’s X?
Write equations for α decay 218Rn + 4He 222Ra 208Po 256Lr 88 86 2 204Pb + 4He 84 82 2 252Md + 4He 103 101 2
Writing equations for α decay 227Ac + 4He 231Pa 225Ac 211Fr 185Au 91 89 2 221Fr + 4He 89 87 2 207At + 4He 87 85 2 181Ir + 4He 79 77 2
α decay 229Th + 4He 90 2 233U 149Gd 232Th 175Pt 237Np 92 145Sm + 4He 2 62 64 228Ra + 4He 88 2 90 171Os + 4He 76 78 2 233Pa + 4He 91 93 2
α decay 4He + 230Ra 234Th 144Nd 146Sm 151Ho 192Pt 90 88 2 4He + 140Ce 60 2 58 4He + 142Nd 62 2 60 4He + 147Tb 67 2 65 4He + 188Os 78 2 76
Radioactive Decay Series • Sometimes 1 transmutation isn’t enough to achieve stability. • Some radioisotopes go through several changes before they achieve stability (and are no longer radioactive).
Alpha Decay 238 = 4 + 234 238 = 4 + 234 92 = 2 + 90
Positron Emission 1p 1n + 0e 1 +1 0
Beta minus emission 1n 1p + 0e 0 1 -1
14C 14N + 0e 6 7 -1 18F 18O + 0e 9 8 +1
How does the mass number or atomic number change in (or or ) decay? • Just go to Table N, find an isotope that decays by alpha decay, write the equation, and see how the mass number (or atomic number) changes. • 226Ra 4 + X so X has to be 222X • X is Ra-222. The mass number decreases by 4 and the atomic number decreases by 2. 2 86 88