fission & fusion - mrs. hayden, fission & fusion . matter and energy • previous studies have...

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  • Fission & Fusion

  • Matter and Energy

    • Previous studies have taught us that

    “matter and energy cannot be created

    nor destroyed”

    • We balance equations to obey this law.

    – 2 H2O  2 H2 + O2

    • We now need to understand that Matter

    and Energy are two forms of the same


  • Mass

    • Matter can be changed into Energy

    • Einstein’s formula above tells us how the change occurs

    • In the equation above:

    E = Energy

    m = Mass

    c = Speed of Light (Universal Constant)

    Energy Light


    E = mc2

  • E = mc2

    • The equation may be read as follows:

    Energy (E) is equal to Mass (m) multiplied by

    the Speed of Light (c) squared

    • This tells us that a small amount of mass

    can be converted into a very large amount of

    energy because the speed of light (c) is an

    extremely large number


  • • Fusion is a nuclear reaction where two light

    atomic nuclei fuse or combine to form a single

    larger, heavier nucleus

    • The fusion process generates tremendous

    amounts energy

    • For fusion to occur, a LARGE amount of

    energy is needed to overcome the electrical

    charges of the nuclei and fuse them together


  • Fusion

    • Fusion reactions do not occur naturally on our

    planet but are the principal type of reaction

    found in stars

    • The large masses, densities, and high

    temperatures of stars provide the initial energies

    needed to fuel fusion reactions

    • The sun fuses hydrogen atoms to produce

    helium, subatomic particles, and vast amounts of


  • How do stars produce energy?

    • Stars are mostly

    Hydrogen that

    produce energy by

    fusion of hydrogen


    • 2 protons (H-1) fuse

    to make a H isotope

    (H-2); then H-1 + H-2

    form an isotope of


    The emission of a positron or a positive electron is referred

    to as beta decay. The positron is accompanied by a

    neutrino, a massless and chargeless particle. Positrons

    are emitted with the same kind of energy spectrum as

    electrons in negative beta decay because of the emission

    of the neutrino.


    light neutrino


  • How do stars produce energy?

    • Finally 4 hydrogen

    nuclei combine

    into 1 Helium


    • A small amount of

    matter changes

    into a huge

    amount of energy.






  • Check Point

    What process creates energy in the Sun? Fusion of hydrogen into helium in the Sun’s core

    generates the Sun’s energy.

    How long ago did fusion generate the energy we now receive as sunlight?

    Fusion created the energy we receive today about a million years ago. This is the time it takes for photons and then convection to transport energy through the solar interior to the photosphere. Once sunlight emerges from the photosphere, it takes only about 8 minutes to reach Earth.


    A reaction in which an atomic

    nucleus of a radioactive element

    splits by bombardment from an

    external source, with

    simultaneous release of large

    amounts of energy, used for

    electric power generation

  • Fission

    • Fission may be defined as the process of

    splitting an atomic nucleus into fission


    • The fission fragments are generally in the

    form of smaller atomic nuclei and neutrons

    • Large amounts of energy are produced by

    the fission process

  • What nuclei can split during

    nuclear fission?

    • Only large nuclei like U or plutonium

    can split apart

    during nuclear


    Click on image

    for animation

  • Chain Reaction

    • Free neutrons produced by fission can hit

    other nuclei emitting more neutrons

    repeating the reaction over and over.

    • A series of fission reactions is called a

    chain reaction.

    • Can only be slowed by using materials

    that will absorb the neutrons.

  • Nuclear Fission

    Neutron induced in U235

    Fission is Exothermic

    The sum of the masses of

    the resulting nuclei is less

    than the original mass

    (about 0.1% less)

    The “missing mass” is converted

    to energy according to E=mc2

  • Nuclear fission:

    A large nucleus splits into several

    small nuclei when impacted by a

    neutron, and energy is released in

    this process

    Nuclear fusion:

    Several small nuclei fuse

    together and release



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