Chapter 18 Nuclear Reactions

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Chapter 18Nuclear Reactions
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Chemical Reactions

• Occur in the outer electron energy level
• Valance electrons

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Nuclear Reactions

• Occur in the nucleus of the atom
• Involve the NUCLEONS
• Nucleons protons neutrons

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Strong Nuclear Force

• Protons are positively charged and repel each
  other
• ? ?
• Strong Nuclear Force the force that causes the
  protons and neutrons in the nucleus to stick
  together and holds the nucleus tightly together.

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Radioactivity

• When the strong force of an atom is not strong
  enough to hold the nucleus together, then the
  atom tends to decay
• The atoms are considered unstable, or radioactive
• The process of decay is called radioactivity and
  in the process particles and energy are released
  and the atom is changed into another type of atom

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ISOTOPES

• Atoms of the same element with a different number
  of neutrons.
• Ex carbon-12 carbon-14
• Carbon-12
• 6 protons
• 6 neutrons
• 6 electrons
• Carbon-14
• 6 protons
• 8 neutrons
• 6 electrons

Carbon 12 is a stable isotope of carbon.
Carbon-14 is unstable or radioactive because the
addition of the two neutrons have disrupted the
strong force and made the nucleus start to decay,
or break apart.
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3 Types of RadioactivityRadioactive Decay

• ALPHA PARTICLE (a)
• BETA PARTICLE (ß)
• GAMMA RAYS (?)

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ALPHA PARTICLE

• 2 protons 2 neutrons
• nucleus of a helium atom
• weakest type of radiation
• can be stopped by a piece of paper
• 12 inches max. distance travel

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• What happens to the numbers of particles in the
  nucleus after alpha decay?

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BETA PARTICLE

• an electron emitted from around the nucleus
• A neutron splits into a proton electron
• The electron is expelled out of the nucleus
• The proton stays and increases the number of
  protons by one.
• The atomic number of the element increases by one
• The element changes into the next higher element
  on the periodic table.
• 100x stronger than an alpha particle

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• What happens to the numbers of particles in the
  nucleus after beta decay?

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Gamma Rays

• An electromagnetic wave
• A packet of energy
• The energy readjustment in the nucleus
• Most powerful form of radiation
• The sun is a great source of gamma radiation

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Gamma Radiation, Cont

• Gamma rays are very harmful to cells. They can
  damage the DNA of your cells and mutate them,
  which can cause cancer
• High amounts of gamma ray exposure can cause
  death
• Low amounts are normal and you are exposed to
  them all the time
• Cannot be easily blocked. Inches of concrete
  lined with lead can stop a gamma ray

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Gamma Ray Photography From Space
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REMEMBER! Gamma rays are light!
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Antoine Henri Becquerel

• In 1896, radioactivity was first discovered.
• Used uranium salts placed them near a
  photographic film plate.
• exposed the film (below)
• Awarded Nobel Prize in 1903 in Physics

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Pierre Marie Curie (1898)

• Discover the radioactive properties of radium
  polonium
• Together awarded the Nobel Prize in 1903
  (physics) along with Henri Becquerel
• Marie is award a second Nobel Prize in 1911
  (chemistry)
• Pierre is killed in an accident in 1906, Marie
  continues working with radioactive substances.
  She eventually dies of cancer

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Transmutation

• changes from one element to another element
  during a and ß decay.
• Alpha Decay mass number decreases by 4 and the
  atomic number decreases by 2
• Beta Decay mass number does not change and the
  atomic number increases by 1

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Alpha Decay

• Uranium-238 has 92 protons
• After alpha decay (2 protons 2 neutrons leave
  the nucleus)
• Becomes Thorium-234 and has 90 protons

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Beta Decay

• Carbon-14 has 6 protons 8 neutrons
• After beta decay (a neutron is split into a
  proton and electron the electron is expelled
  from the nucleus)
• Becomes Nitrogen-14 and has 7 protons and 7
  neutrons

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Half Life

• the time it takes for one half of the mass of a
  radioactive substance to decay.
• Ex carbon-14 5730 years
• 100 gram sample
• In 5730 yrs 50 grams C-14 50 grams N-14
• In11,460 yrs 25 grams C-14 75 grams N-14
• In 17,190 yrs 12.5 grams C-14 87.5 grams N-14

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Radioactive Dating

• Half life is used by scientists to find out how
  old a fossil or a rock is
• Carbon 14 is often used to date fossils
• What type of isotope used depends on the material
  being dated
• Uranium is often used to date rocks because many
  rocks contain uranium already

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Detecting Radioactivity

• Cloud chambers track alpha and beta particles
• Chamber is filled with a cloud of vapor
• Alpha particles leave short thick trails
• Beta particles leave long thin trails

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Bubble Chamber

• Holds a super heated liquid that doesnt boil due
  to high pressure
• When a radioactive particle passes through the
  liquid, trails of bubbles form

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Geiger Counter

• Pops or clicks in the presence of radiation
• Uses electricity and current to cause a flow of
  electrons
• The current is amplified to produce a clicking
  sound

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Background Radiation

• You are exposed to radiation every day
• Sources of background radiation vary and amounts
  are usually not harmful

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Nuclear Reactions

• Nuclear Fission
• Nuclear Fusion

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Nuclear Fission

• the splitting of the nucleus into two smaller
  nuclei
• Neutrons are used to split the nucleus
• Additional neutrons are released to continue on
  to hit/split other nuclei

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Chain Reactions

• Critical Mass (required) concentration of
  radioactive atoms in a sample.
• Controlled Chain Reaction many of the neutrons
  that are produced are absorbed in control rods
  prevent excess energy to be released.
• Ex. Nuclear Power Plants
• Uncontrolled Chain Reaction all the neutrons
  are allowed to continue to hit/split other nuclei
  causing massive amounts of energy to be released
  all at once.
• Ex. Atomic Bomb (used on Japan in 1945)

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Controlled Chain Reaction
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Generating Electricity

• Nuclear power is only one way to generate
  electricity
• It is often cheaper and easier than other forms
  of energy (ie using wind or coal or water)
• However, there are safety concerns that you must
  take into consideration

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Nuclear Reactors

• Used to generate electricity
• Used to power ships, submarines
• Risk of meltdown, must be kept cool to prevent
  uncontrolled chain reactions

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Nuclear Reactor
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Three Mile Island Accident

• March 28, 1979 Harrisburg PA Three Mile Island
  Nuclear Power Plant A partial meltdown occurred
  in one reactor due to a stuck valve. Negligible
  amounts of radiation were released into the
  environment

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Chernobyl - April 26,1986

• Power Plant in the Ukraine
• Explosion and fire that was caused by a power
  surge
• 31 people died of acute radiation sickness
• You still cant live in that area today
• Crops were affected, many cases of cancer
  recorded, especially in children

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Chernobyl
Pripyat, Ukraine
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Fukushima - March 11, 2011

• Ongoing nuclear accident in Japan at the
  Fukushima power plant
• Caused partial or full meltdown to reactor,
  thanks to earthquake and Tsunami
• Power failure to coolant main cause
• Effects of the disaster are ongoing and unknown
  at this time

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Uncontrolled Chain Reaction
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Nuclear Fusion

• the joining of two smaller nuclei into a single
  larger nucleus
• Powers the sun, very hard to duplicate on Earth
  because of the high pressure and temperature
  needed
• Extremely more powerful release of energy than
  fission
• Also known as a thermonuclear reaction
• ex H-bomb and the sun/stars

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Fusion Explosions
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