CHAPTER 9 Nuclear Energy

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CHAPTER 9 Nuclear Energy

• I. Radioactivity
• (pg.284-292)

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Radioactive Elements
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A. Definitions

• Radioactivity
• Process of unstable nuclei of elements becoming
  stable through emitting particles or releasing
  energy away from the atom
• Also called nuclear decay

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Definitions

• During nuclear decay, the element can transform
  into a different isotope of the same element or
  to a different element completely.
• Transmutation
• process of changing one element into another
  element by nuclear decay

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Definitions

• Nuclear radiation is the released energy and
  matter during nuclear decay.
• This can have both positive and negative effects
  for life on earth.

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Definitions

• Isotopes elements that have the same number of
  protons but different number of neutrons in their
  nuclei.

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Isotopes

• Carbon-12, Carbon-13, Carbon-14

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Where does this take place?

• Radioactivity (nuclear decay) happens in the
  nucleus of the atom.

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B. Types of Radiation

• Alpha (?)
• helium nucleus

paper
2

• Beta-minus (?-)
• electron

plastic
1-

• Gamma (?)
• high-energy photon

lead
0
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Types of Radiation

• Neutron emission (n) 1
• 0 n 0 charge

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C. Nuclear Decay

• Why some nuclei decay
• to obtain a stable ratio of neutrons to protons

Stable
Unstable (radioactive)
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C. Nuclear Decay
TRANSMUTATION

• Alpha Emission

• Beta Emission

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Example

• Actinium-217 decays by releasing an alpha
  particle. Write the equation for this decay
  process and determine what element is formed.
• Step 1 Write the equation with the original
  element on the reactant side and products on the
  right side.

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Example

• 217 A 4
• 89 Ac ? Z X 2 He
• Step 2 Write math equations for the atomic and
  mass numbers.
• 217 A 4
• 89 Z 2

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Example

• Step 3 Rearrange the equations.
• A 217 4 Z 89 - 2
• Step 4Solve for the unknown value, and rewrite
  the equation with all nuclei.
• A 213 Z 87

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Example

• 217 213 4
• 89 Ac ? 87 Fr 2 He
• This is an example of alpha decay.

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D. Half-life

• Half-life (t½)
• time it takes for half of the radioactive nuclei
  in a sample to decay

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Half-life
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If we start out with 1 gram of the
parent isotope, after the passage of 1 half-life,
there will be 0.5 gram of the parent isotope
left. 
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D. Half-life

• How much of a 20-g sample of sodium-24 would
  remain after decaying for 30 hours? Sodium-24
  has a half-life of 15 hours.

GIVEN total time 30 hours t1/2 15
hours original mass 20 g
WORK number of half-lives 2 20 g 2 10 g
(1 half-life) 10 g 2 5 g (2
half-lives) 5 g of 24Na would remain.
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Nuclear Forces

• There are two types of forces in the nucleus.
• Strong nuclear force helps attract the protons
  and neutrons in the nucleus and keep them
  together.
• Repulsive force- protons repel each other because
  they are the same charge

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Nuclear Forces
In stable atoms, the attractive forces are
stronger than the repulsive forces.
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A. F ission

• splitting a nucleus into two or more smaller
  nuclei
• some mass is converted to large amounts of energy

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A. F ission

• chain reaction - self-feeding reaction

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Fission

• Chain reactions can be controlled and used to
  create electricity in nuclear power plants.
• The minimum amount of a substance that can
  undergo a fission reaction and sustain a chain
  reaction is called critical mass.

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B. Fusion

• combining of two nuclei to form one nucleus of
  larger mass
• produces even more energy than fission
• occurs naturally in stars

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Fusion
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Nuclear Radiation in Life

• Background radiation is nuclear radiation that is
  around you from natural sources like the sun,
  soil, rocks, and space.
• A rem or millirem (1 rem 1000millirems) is the
  unit for radiation.

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Nuclear Radiation in Life

• A safe limit is set at 5000 millirems/year.
• Occupation X-ray tech, flight attendant
• Where you live- high elevation, near rocks
• Activities - smoking

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A. Nuclear Power

• Fission Reactors

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A. Nuclear Power

• Fusion Reactors (not yet sustainable)

National Spherical Torus Experiment
Tokamak Fusion Test Reactor Princeton University
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A. Nuclear Power
FISSION
FUSION
vs.

• 235U is limited
• danger of meltdown
• toxic waste
• thermal pollution

• Hydrogen is abundant
• no danger of meltdown
• no toxic waste
• not yet sustainable

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Other benefits to radiation

• Smoke detectors
• Disease detection
• Ultra sound
• CT scan
• MRI
• Cancer treatment