Nuclear Forces

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Nuclear Forces Nuclear Decay

• Where did the elements come from anyway?

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Lifecycle of Stars Presentations

• Sing a song, do a dance, perform a puppet show,
  recite a poem whatever you choose that
  demonstrates the lifecycle of medium, large, and
  huge stars.
• Take 5 min. to wrap up any lose ends.
• The most impressive, and correct, presentation
  wins free article passes.

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Nuclear Forces Nuclear Decay

• The Main Idea
• The 4 fundamental forces in nature
• strong nuclear force - force that holds the
  nucleus together

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Strong Nuclear Force
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Nuclear Forces Nuclear Decay

• The Main Idea
• The 4 fundamental forces in nature
• strong nuclear force - force that holds the
  nucleus together
• weak force allows quarks to change flavors
  causes transmutations

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Weak Force
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Nuclear Forces Nuclear Decay

• The Main Idea
• The 4 fundamental forces in nature
• strong nuclear force - force that holds the
  nucleus together
• weak force allows quarks to change flavors
  causes transmutations
• electromagnetic forces holds atoms and
  molecules together

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Electromagnetic Force
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Nuclear Forces Nuclear Decay

• The Main Idea
• The 4 fundamental forces in nature
• strong nuclear force - force that holds the
  nucleus together
• weak force allows quarks to change flavors
  causes transmutations
• electromagnetic forces holds atoms and
  molecules together
• gravity force of attraction between objects
  that depends on mass and distance

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Gravity
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Nuclear Forces Nuclear Decay

• The Main Idea
• The Nucleus
• made up of protons and neutrons
• the forces that hold the nucleus together tend to
  be stronger than the forces that make it want to
  come apart

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Nuclear Forces Nuclear Decay

• The Main Idea
• The Nucleus
• made up of protons and neutrons
• the forces that hold the nucleus together tend to
  be stronger than the forces that make it want to
  come apart
• elements with large nuclei
• have large atomic numbers
• nuclei are unstable
• nuclei can decay, or break apart, over time
• as the nuclei decay, their overall mass decreases

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Uranium
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Nuclear Forces Nuclear Decay

• Why is it so easy for a large mass atom to break
  apart?
• What forces cause this to happen?

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Nuclear Forces Nuclear Decay

• The Main Idea
• The Nucleus
• made up of protons and neutrons
• the forces that hold the nucleus together tend to
  be stronger than the forces that make it want to
  come apart
• elements with large nuclei
• elements with small nuclei
• the overall mass may increase if the nucleus is
  unstable
• they may join nuclei, forming a new element with
  a larger nucleus
• In either case, a tremendous amount of energy is
  released

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Nuclear fission reaction
Nuclear fusion reaction
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Nuclear Forces Nuclear Decay

• Isotopes
• atoms of the same element have the same number of
  protons
• different atoms of the same element may have
  different numbers of neutrons these are
  isotopes
• isotopes of the same element have the same atomic
  number but different atomic masses

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Nuclear Forces Nuclear Decay

• Isotopes
• Radioactivity
• some isotopes are radioactive
• radioactivity is the spontaneous release of
  particles or radiation (energy) from the nucleus
  of an atom.
• radioisotopes are isotopes that are unstable and
  radioactive.
• identified by symbol and atomic mass
• example, C-14
• an isotope of the element carbon
• has an atomic mass of 14 amu (atomic mass units)
• isotopes of all elements with an atomic number
  greater than 84 are radioactive

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Nuclear Forces Nuclear Decay

• Types of Radioactive Decay
• As radioactive nuclei decay, they release
  particles and energy
• the release of particles from the nucleus may
  cause the formation of a new element
• ie, new atomic number
• Transmutation the process that takes place when
  the nucleus of one atom emits radiation and
  changes to an atom of another element

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Nuclear Forces Nuclear Decay

• Types of Radioactive Decay
• Alpha Decay
• gives off alpha particles
• an alpha particle consists of 2 protons and 2
  neutrons
• the particle moves slowly
• has little penetrating power
• sheets of paper or clothing can stop alpha
  particles

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Alpha Decay of Americium-241 to Neptunium-237
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Nuclear Forces Nuclear Decay

• Types of Radioactive Decay
• Beta Decay
• gives off beta particles
• a beta particle has the same charge and mass as
  an electron but comes from the nucleus
• move fast
• have more penetrating power than alpha particles
• can be stopped by heavy clothing or wool

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Beta Decay of Hydrogen-3 to Helium-3
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Nuclear Forces Nuclear Decay

• Types of Radioactive Decay
• Gamma Decay
• a gamma ray is a high energy photon
• waves similar to x-rays, but have higher energy
• have no mass
• have extreme penetrating power
• thick lead or concrete shielding can stop a gamma
  ray

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Gamma Decay of Helium-3
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Nuclear Forces Nuclear Decay

• Nuclear fission
• any change that involves the nucleus of an atom
  is a nuclear reaction
• when a large nucleus splits into two smaller
  nuclei, that is nuclear fission
• Ex) neutron U-235 ? Kr-92 Ba-141 3 neutrons
• U-235 element is struck with a neutron, splitting
  its nucleus
• 3 free neutrons are also released
• these free neutrons may strike another U-235
  causing them to undergo fission as well

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Nuclear Fission
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Nuclear Forces Nuclear Decay

• Nuclear fission
• When the products and energy from one reaction
  start further reactions, it is called a chain
  reaction

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Nuclear Fission Chain Rxn
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Nuclear Forces Nuclear Decay

• Nuclear fission
• When the products and energy from one reaction
  start further reactions, it is called a chain
  reaction
• A large amount of energy is released from a very
  small amount of fuel the nucleus
• controlled nuclear fission reactors are used in
  some power pants that generate electricity
• can also power naval submarines

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Nuclear Forces Nuclear Decay

• Nuclear fusion
• involves joining instead of splitting nuclei
• two smaller nuclei join to form an atom with a
  large nucleus
• example equation H H ? He
• This reaction drives the formation of stars as
  well as releases a huge amount of energy

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Nuclear Forces Nuclear Decay

• Nuclear fission
• Fusion is a much cleaner process than fission
• it takes a great amount of energy to fuse the two
  positive H nuclei together
• research is being done to find a way to control
  fusion reactions to provide clean safe energy
  from nuclear reactions

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Nuclear Forces Nuclear Decay

• Energy from the Nucleus
• Energy released from a nuclear reaction is called
  nuclear energy
• Emc2
• Einsteins famous equation
• demonstrates how a small amount of mass (m) can
  be converted into a large amount of energy (E)
• c represents the speed of light (3X108 m/sec)