Nuclear Reactions Natural Transmutation 1 term on reactant
- Slides: 35
Nuclear Reactions
Natural Transmutation 1 term on reactant side Original isotope 2 terms on product side Emitted Particle New Isotope Happens all by itself (spontaneous) Not affected by anything in environment
Natural Transmutation 16 N 7 1 term on reactant side 0 e -1 + 16 O 8 2 terms on product side
Artificial Transmutation • Cause it to happen by smashing particles into one another • 2 terms on reactant side • Original Isotope • Particle that hits it – neutron, proton, or -particle • Product side: usually 2 terms
Artificial Transmutation 13 27 Al + 4 He 2 Original isotope or target nucleus 30 P + 1 n 15 0 “Bullet” -what hits isotope
Artificial Transmutation 27 Al 13 14 N 7 + 4 He 30 P + 1 n 2 15 0 + 42 He 178 O + 11 H 75 As 33 + 4 He 78 Br + 1 n 2 0 35 37 Cl 17 + 1 n 38 Cl 17 0 All of these equations have 2 reactants!
Bombarding with Protons or Protons and -particles have positive charge and mass • do some damage when hit target nucleus • must be accelerated to high speeds to overcome repulsive forces between nucleus & particle (both are +)
What is an accelerator? • vacuum chamber (usually a long pipe) – surrounded by vacuum pumps, magnets, radiofrequency cavities, high voltage instruments and electronic circuits • inside the pipe particles are accelerated to very high speeds then smashed into each other
Fission Reaction Splitting heavy nucleus into 2 lighter nuclei q Requires a critical mass of fissionable isotope Controlled – nuclear reactor Uncontrolled – bomb
Fission q. Reactant side: 2 terms • 1 heavy isotope (examples: U-235 or Pu-239) • Bombarding particle – usually a neutron • Product side: at least 2 terms • 2 medium-weight isotopes • 1 or more neutrons • Huge amount of energy is released • Fission = Division
Fission 235 U + 1 n 91 Kr + 235 U 92 1 n + energy + 1 n 72 Zn + 160 Sm + 4 62 92 0 0 36 30 142 Ba 56 + 31 n + energy 0 0 More than 200 different product isotopes identified from fission of U-235 A small amount of mass is converted to energy according to E = mc 2
Fission Chain Reaction
Fusion • Reactant side has 2 small nuclei: – H + H; H + He; He + He • Product side: – 1 nucleus (still small) and maybe a particle • Source of sun’s energy • 2 nuclei unite 2 H 1 + 3 H 4 He + 1 n + energy 1 2 0
CERN 27 kilometer ring • Particles travel just below speed of light • In 10 hrs: particles make 400 million revolutions of the ring
Fermi. Lab 4 miles in circumference!
Balancing Nuclear Equations
Nuclear Equations - tasks • Identify type (4 types) • Balance to find 1 unknown term
Natural Transmutation – ID • 1 term on reactant side – starting isotope • 2 terms on product side – ending isotope and emitted particle • Type of particle emitted characteristic of isotope – Table N
Nuclear Equations • To balance: use conservation of both atomic number & mass number • Mass number = left superscript • Atomic Number = left subscript
Balancing Nuclear Equations 16 N 7 0 e -1 + 16 O 8 Conservation of mass number: 16 = 0 + 16 Conservation of atomic number: 7 = -1 + 8
Writing Equations • Write the equation for the decay of Thorium-232 • Use Table N to find the decay mode: α • Write the initial equation: 232 Th 4 He + X 90 2 figure out what element it turned into
Write an equation for the α decay of Am-241 95 Am 4 He + YX What’s X? 2 Z
so Y = 228 232 = 4 + Y 232 Th 90 4 He + 2 Y Z X Conservation of Mass Number: sum of mass numbers on left side must = sum of mass numbers on right side
232 Th 90 42 He + 228 Z X 2 Z 90 = 2 + Z so Z = 88 Conservation of Atomic Number: sum of atomic numbers on left side must = sum of atomic numbers on right side
232 Th 90 4 He + 228 X 2 88 Use the PT to find X: 232 Th 90 4 He + 228 Ra 2 88 X = Ra
Alpha (α) decay: 233 U 92 232 Th 90 90 175 Pt 78 229 Th 228 Ra 2 + 88 171 Os 76 + 4 He 2 + 2 4 He
How does the mass number or atomic number change in α, β or γ decay? • go to Table N: – find isotope that decays by alpha or β decay – write the equation – see how the mass number (or atomic number) changes • 226 4 + X so X has to be Ra 88 2 • X is Rn-222 86 X – mass number decreases by 4; atomic number decreases by 2
Write an equation for the decay of Am-241 = 4 241 95 + Y so Y = 237 Am 4 He + YX 95 2 = 2 What’s X? Z + Z so Z = 93 X = Np
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)
β- β+ 18 F 9 14 C 6 147 N + 188 O + +10 e 0 e -1
How does the mass number or atomic number change in or decay? • Go to Table N; find an isotope that decays by α, or , write the equation; see how the mass number (or atomic number) changes • 226 Ra 4 + X so X has to be 222 X 88 2 • X is Ra-222 – mass number decreases by 4 – atomic number decreases by 2 86
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