Nuclear Reactions

Balancing Nuclear Equations Conservation of Atomic Number (subscript) Conservation of Atomic Mass (superscript)

Balancing Nuclear Equations 16N  0e + 16O -1 7 8 Conservation of mass number: 16 = 0 + 16 Conservation of atomic number: 7 = -1 + 8

Natural Transmutation 1 term on the reactant side Original isotope 2 terms on the product side Emitted Particle New Isotope Happens all by itself. Not affected by anything in the environment.

Natural Transmutation 16N  0e + 16O 7 -1 8 1 term on reactant side 2 terms on product side

Artificial Transmutation We cause it to happen by smashing particles into one another. 2 terms on the reactant side. Original Isotope or Target Particle that hit it or bullet: neutron, proton, or -particle Product side usually has 2 terms.

Artificial Transmutation 27Al + 4He  30P + 1n 13 2 15 Original isotope or target nucleus “Bullet”

Bombarding with Protons,  Protons and -particles have positive charge and mass. They can do some damage when they hit the target nucleus. Protons and -particles have to be accelerated to high speeds to overcome repulsive forces. (The nucleus they are aiming for is also positive.) Use magnetic and electric fields to accelerate them.

What is an accelerator? An accelerator consists of a vacuum chamber, usually a long pipe, surrounded by vacuum pumps, magnets, radio-frequency cavities, high voltage instruments and electronic circuits. Inside the pipe, particles are accelerated to very high speeds & smashed into each other.

FermiLab 4 miles in circumference!

CERN 27 kilometer ring. Particles travel at just below the speed of light. In 10 hrs, the particles make 400 million revolutions of the ring.

SLAC LBL

Neutron Capture Neutrons don’t have to be accelerated. They’re neutral so they aren’t repelled by a positive nucleus. Don’t need high K.E. to overcome repulsive forces. So don’t need accelerators. It’s a good thing – we can’t accelerate neutrons.

Artificial Transmutation 27Al + 4He  30P + 1n All of these equations have 2 reactants! 13 2 15 14N + 4He  17O + 1H 1 2 8 7 75As + 4He  78Br + 1n 2 35 33 37Cl + 1n  38Cl 17 17

2 more kinds of nuclear equations Fission Fusion Both have 2 reactants Equations have distinctive features, so easy to tell them from artificial transmutation

Fission Reaction Involves splitting a heavy nucleus into 2 lighter nuclei.

Fission Involves splitting a heavy nucleus into 2 lighter nuclei. Reactant side has 2 terms: 1 heavy isotope, U-235 or Pu-239 Bombarding particle – usually a neutron Product side has at least 2 terms: 2 medium-weight isotopes 1 or more neutrons Huge amount of energy is released. Fission = Division

Fission 235U + 1n  91Kr + 142Ba + 31n + energy 56 92 36 92 36 235U + 1n  72Zn + 160Sm + 41n + energy 62 92 30 More than 200 different product isotopes from the fission of U-235 have been identified. A small amount of mass is converted to energy by E = mc2.

Fission Chain Reaction

Fission Chain Reaction Requires a critical mass of fissionable isotope. Controlled – nuclear reactor. Uncontrolled – bomb. Animation of nuclear reactor

Fusion Reactant side has 2 small nuclei – H + H or H + He or He + He. Product side has 1 (still pretty small nucleus) and maybe a particle. Source of sun’s energy. 2 nuclei unite. 2H + 3H  4He + 1n + energy 1 1 2

Inertial Confinement - Fusion

Magnetic Confinement - fusion