Warm Up

1
Warm- Up

• Welcome Back
• No talking
• List the 3 main particles in an atom and whether
  they are in the nucleus or outside the nucleus.
• How is energy generated at nuclear power plants?

2
Nuclear Chemistry Basic Concepts
Topic 26
Nuclear Radiation

• Nuclear chemistry is the study of the structure
  of atomic nuclei and the changes they undergo.

3
Nuclear Chemistry Basic Concepts
Topic 26
Types of Radiation

• As you may recall, isotopes are atoms of the same
  element that have different numbers of neutrons.

• Isotopes of atoms with unstable nuclei are called
  radioisotopes.

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Nuclear Chemistry Basic Concepts
Topic 26
Types of Radiation

• These unstable nuclei emit radiation to attain
  more stable atomic configurations in a process
  called radioactive decay.

• During radioactive decay, unstable atoms lose
  energy by emitting one of several types of
  radiation.

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Nuclear Chemistry Basic Concepts
Topic 26
Types of Radiation

• The three most common types of radiation are
• alpha (a)
• beta (ß)
• gamma (?).

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Nuclear Chemistry Basic Concepts
Topic 26
Types of Radiation
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Nuclear Chemistry Basic Concepts
Topic 26
Types of Radiation

• The charge of an alpha particle is 2 due to the
  presence of the two protons.

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Nuclear Chemistry Basic Concepts
Topic 26
Types of Radiation

• Alpha radiation consists of a stream of alpha
  particles.

• Radium-226, an atom whose nucleus contains 88
  protons and 138 neutrons, undergoes alpha decay
  by emitting an alpha particle.

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Nuclear Chemistry Basic Concepts
Topic 26
Types of Radiation

• Notice that after the decay, the resulting atom
  has an atomic number of 86, a mass number of 222,
  and is no longer radium.

• The newly formed radiosiotope is radon-222.

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Nuclear Chemistry Basic Concepts
Topic 26
Types of Radiation

• The particles involved are balanced. That is, the
  sum of the mass numbers (superscripts) and the
  sum of the atomic numbers (subscripts) on each
  side of the arrow are equal.

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Nuclear Chemistry Basic Concepts
Topic 26
Types of Radiation

• Because of their mass and charge, alpha particles
  are relatively slow-moving compared with other
  types of radiation.

• Thus, alpha particles are not very penetratinga
  single sheet of paper stops alpha particles.

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Nuclear Chemistry Basic Concepts
Topic 26
Types of Radiation

• A beta particle is a very-fast moving electron
  that has been emitted from a neutron of an
  unstable nucleus.

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Nuclear Chemistry Basic Concepts
Topic 26
Types of Radiation

• The 1 subscript denotes the negative charge of
  the particle.

• Beta radiation consists of a stream of
  fast-moving electrons.

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Nuclear Chemistry Basic Concepts
Topic 26
Types of Radiation

• An example of the beta decay process is the decay
  of iodine-131 into xenon-131 by beta-particle
  emission.

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Nuclear Chemistry Basic Concepts
Topic 26
Types of Radiation

• Note that the mass number of the product nucleus
  is the same as that of the original nucleus (they
  are both 131), but its atomic number has
  increased by 1 (54 instead of 53).

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Nuclear Chemistry Basic Concepts
Topic 26
Types of Radiation

• This change in atomic number, and thus, change in
  identity, occurs because the electron emitted
  during the beta decay has been removed from a
  neutron, leaving behind a proton.

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Nuclear Chemistry Basic Concepts
Topic 26
Types of Radiation

• Because beta particles are both lightweight and
  fast moving, they have greater penetrating power
  than alpha particles.

• A thin metal foil is required to stop beta
  particles.

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Nuclear Chemistry Basic Concepts
Topic 26
Types of Radiation

• As you can see from the symbol, both the
  subscript and superscript are zero.

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Nuclear Chemistry Basic Concepts
Topic 26
Types of Radiation

• Thus, the emission of gamma rays does not change
  the atomic number or mass number of a nucleus.

• Gamma rays almost always accompany alpha and beta
  radiation, as they account for most of the energy
  loss that occurs as a nucleus decays.

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Nuclear Chemistry Basic Concepts
Topic 26
Types of Radiation

• For example, gamma rays accompany the alpha-decay
  reaction of uranium-238.

• The 2 in front of the ? symbol indicates that two
  gamma rays of different frequencies are emitted.

• Because gamma rays have no effect on mass number
  or atomic number, it is customary to omit them
  from nuclear equations.

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Nuclear Chemistry Basic Concepts
Topic 26
Radioactive Decay

• It may surprise you to learn that of all the
  known isotopes, only about 17 are stable and
  dont decay spontaneously.

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Nuclear Chemistry Basic Concepts
Topic 26
Beta Decay

• The nitrogen-14 atom now has a stable
  neutron-to-proton ratio of 1 1.

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Nuclear Chemistry Basic Concepts
Topic 26
Beta Decay

• Thus, beta emission has the effect of increasing
  the stability of a neutron-rich atom by lowering
  its neutron-to-proton ratio.

• The resulting atom is closer to, if not within,
  the band of stability.

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Nuclear Chemistry Basic Concepts
Topic 26
Alpha Decay

• All nuclei with more than 83 protons are
  radioactive and decay spontaneously.

• Both the number of neutrons and the number of
  protons must be reduced in order to make these
  radioisotopes stable.

• These very heavy nuclei often decay by emitting
  alpha particles.

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Nuclear Chemistry Basic Concepts
Topic 26
Alpha Decay

• For example, polonium-210 spontaneously decays by
  alpha emission.

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Nuclear Chemistry Basic Concepts
Topic 26
Balancing a Nuclear Equation

• You are given that a thorium atom undergoes alpha
  decay and forms an unknown product.

• Thorium-230 is the initial reactant, while the
  alpha particle is one of the products of the
  reaction. The reaction is summarized below.

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Nuclear Chemistry Basic Concepts
Topic 26
Balancing a Nuclear Equation

• You must determine the unknown product of the
  reaction, X.

• This can be done through the conservation of
  atomic number and mass number.

• The periodic table can then be used to identify
  X.

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Nuclear Chemistry Basic Concepts
Topic 26
Balancing a Nuclear Equation

• Known

• Unknown

30
Nuclear Chemistry Basic Concepts
Topic 26
Balancing a Nuclear Equation

• Using each particles mass number, make sure mass
  number is conserved on each side of the reaction
  arrow.

• Thus, the mass number of X is 226.

• Using each particles atomic number, make sure
  atomic number is conserved on each side of the
  reaction arrow.

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Nuclear Chemistry Basic Concepts
Topic 26
Balancing a Nuclear Equation

• Thus, the atomic number of X is 88. The periodic
  table identifies the element as radium (Ra).

• Write the balanced nuclear equation.

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Basic Assessment Questions
Topic 26
Question 1
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Basic Assessment Questions
Topic 26
Answer
34
Basic Assessment Questions
Topic 26
Question 2
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Basic Assessment Questions
Topic 26
Answer
36
Basic Assessment Questions
Topic 26
Question 4
Write a balanced nuclear equation for the beta
decay of the following radioisotope.
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Basic Assessment Questions
Topic 26
Answer
38
Nuclear Chemistry Additional Concepts
Topic 26
Additional Concepts
39
Nuclear Chemistry Additional Concepts
Topic 26
Radioactive Decay Rates

• Radioactive decay rates are measured in
  half-lives.

• A half-life is the time required for one-half of
  a radioisotopes nuclei to decay into its
  products.

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Nuclear Chemistry Additional Concepts
Topic 26
Radioactive Decay Rates

• For example, the half-life of the radioisotope
  strontium-90 is 29 years.

• If you had 10.0 g of strontium-90 today, 29 years
  from now you would have 5.0 g left.

• The decay continues until negligible strontium-90
  remains.

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Nuclear Chemistry Additional Concepts
Topic 26
Radioactive Decay Rates

• The graph shows the percent of a stontium-90
  sample remaining over a period of four
  half-lives.

• With the passing of each half-life, half of the
  strontium-90 sample decays.

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Nuclear Chemistry Additional Concepts
Topic 26
Calculating Amount of Remaining Isotope

• Iron-59 is used in medicine to diagnose blood
  circulation disorders.

• The half-life of iron-59 is 44.5 days.

• How much of a 2.000-mg sample will remain after
  133.5 days?

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Nuclear Chemistry Additional Concepts
Topic 26
Calculating Amount of Remaining Isotope

• You are given a known mass of a radioisotope with
  a known half-life.

• You must first determine the number of half-lives
  that passed during the 133.5 day period.

• Then use the exponential decay equation to
  calculate the amount of the sample remaining.

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Nuclear Chemistry Additional Concepts
Topic 26
Calculating Amount of Remaining Isotope

• Known

• Initial amount 2.000 mg

• Elapsed time (t) 133.5 days

• Half-life (T) 44.5 days

• Unknown

• Amount remaining ? mg

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Nuclear Chemistry Additional Concepts
Topic 26
Calculating Amount of Remaining Isotope

• Determine the number of half-lives passed during
  the 133.5 days.

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Nuclear Chemistry Additional Concepts
Topic 26
Calculating Amount of Remaining Isotope

• Divide the initial amount in half (divide by 2)
  however many half-lives have passed
• In this case 3 half lives have passed so we dive
  the initial amount by 2, 3 times.
• Amount left 2mg/2 1mg/2 .5mg/2

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Nuclear Chemistry Additional Concepts
Topic 26
Radiochemical Dating

• Chemical reaction rates are greatly affected by
  changes in temperature, pressure, and
  concentration, and by the presence of a catalyst.

• In contrast, nuclear reaction rates remain
  constant regardless of such changes.

• In fact, the half-life of any particular
  radioisotope is constant.

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Nuclear Chemistry Additional Concepts
Topic 26
Radiochemical Dating

• Because of this, radioisotopes can be used to
  determine the age of an object.

• The process of determining the age of an object
  by measuring the amount of a certain radioisotope
  remaining in that object is called radiochemical
  dating.

49
Warm-Up

• Write the nuclear equation for the alpha decay of
  Ac-227.
• Write the nuclear equation for the beta decay of
  Pa-233
• What stops alpha, beta, and gamma particles
  respectively?

50
Nuclear Chemistry Additional Concepts
Topic 26
Nuclear fission

• Heavy atoms (mass number gt 60) tend to break into
  smaller atoms, thereby increasing their
  stability.

• The splitting of a nucleus into fragments is
  called nuclear fission.

• Nuclear fission releases a large amount of
  energy.

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Nuclear Chemistry Additional Concepts
Topic 26
Nuclear fission

• One fission reaction can lead to more fission
  reactions, a process called a chain reaction.

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Nuclear Chemistry Additional Concepts
Topic 26
Nuclear reactors

• Nuclear power plants use the process of nuclear
  fission to produce heat in nuclear reactors.

• The heat is used to generate steam, which is then
  used to drive turbines that produce electricity.

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Nuclear Chemistry Additional Concepts
Topic 26
Nuclear reactors

• Cadmium and boron are used to keep the fission
  process under control.

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Nuclear Chemistry Additional Concepts
Topic 26
Nuclear fusion

• The combining of atomic nuclei is called nuclear
  fusion.

• For example, nuclear fusion occurs within the
  Sun, where hydrogen atoms fuse to form helium
  atoms.
• Go to slide 39

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Nuclear Chemistry Additional Concepts
Topic 26
Applications and Effects of Nuclear
Reactions

• Geiger counters, scintillation counters, and film
  badges are devices used to detect and measure
  radiation.

56
Nuclear Chemistry Additional Concepts
Topic 26
Applications and Effects of Nuclear
Reactions

• Geiger counters use ionizing radiation, which
  produces an electric current in the counter, to
  rate the strength of the radiation on a scale.

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Nuclear Chemistry Additional Concepts
Topic 26
Applications and Effects of Nuclear
Reactions

• Ionizing radiation is radiation that is energetic
  enough to ionize matter upon collision.

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Nuclear Chemistry Additional Concepts
Topic 26
Applications and Effects of Nuclear
Reactions

• With proper safety procedures, radiation can be
  useful in industry, in scientific experiments,
  and in medical procedures.

• A radiotracer is a radioisotope that emits
  non-ionizing radiation and is used to signal the
  presence of an element or of a specific
  substance.

• Radiotracers are used to detect diseases and to
  analyze complex chemical reactions.

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Nuclear Chemistry Additional Concepts
Topic 26
Applications and Effects of Nuclear
Reactions

• Any exposure to radiation can damage living
  cells.

• Gamma rays are very dangerous because they
  penetrate tissues and produce unstable and
  reactive molecules, which can then disrupt the
  normal functioning of cells.

60
Nuclear Chemistry Additional Concepts
Topic 26
Applications and Effects of Nuclear
Reactions

• The amount of radiation the body absorbs (a dose)
  is measured in units called rads and rems.

• Everyone is exposed to radiation, on average
  100300 millirems per year. A dose
  exceeding 500 rem can be fatal.

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Additional Assessment Questions
Topic 26
Question 1
The Sun is powered by the fusion of hydrogen
atoms into helium atoms. When the Sun has
exhausted its hydrogen supply, it could fuse
helium-4, forming carbon-12. Write a balanced
nuclear equation for this process.
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Additional Assessment Questions
Topic 26
Answer
63
Additional Assessment Questions
Topic 26
Question 2
64
Additional Assessment Questions
Topic 26
Answer
65
Additional Assessment Questions
Topic 26
Question 3
What is the difference between nuclear fusion and
nuclear fission?
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Additional Assessment Questions
Topic 26
Answer
Nuclear fusion is the combining of nuclei to form
a single nucleus. Nuclear fission is the
splitting of a nucleus into fragments.