Nuclear Physics

1
Nuclear Physics
2
Radioactivity

• Radioisotopes are unstable isotopes whose nuclei
  gain stability by spontaneously undergoing
  changes.
• These changes are accompanied by the emission of
  large amounts of energy.
• Radioactive decay is the process by which
  materials give off this energy.
• The penetrating rays and particles that are
  emitted during these changes are called
  radiation.
• Eventually unstable radioactive isotopes are
  transformed into stable isotopes of a different
  element.

3
What holds the nucleus together?

• The nucleus contains the positively charged
  protons and neutral neutrons.
• There is a repulsive force between the protons
  (like charges repel).
• The strong nuclear force (also called the strong
  force) acts between the protons and neutrons in
  the nucleus holding them together.
• This strong force is 100 times stronger than the
  repulsive force between protons.
• The range of this force is so short that in large
  nuclei the repulsive force is greater resulting
  in an unstable nuclei.
• When a radioactive isotope decays, some of the
  energy holding the nucleus together is released
  in the form of a radioactive particle with mass
  and kinetic energy.

4
Radioactive Isotopes

• All elements consist of at least one radioactive
  isotope.
• Isotopes that have too many or too few neutrons
  (atomic mass larger or smaller than the average)
  tend to be radioactive.
• All isotopes with an atomic number greater than
  83 are radioactive.

5
Identify the radioactive isotope

• 11H
• 614C
• 816O
• 714N

6
Identify the radioactive isotope

• Chlorine-35
• Carbon-12
• Lead-207
• Potassium-40

7
Types of Radiation

• Alpha radiation
• Beta radiation
• Gamma radiation

8
Alpha Radiation

• Alpha radiation consists of helium nuclei that
  are emitted from a radioactive isotope.
• Alpha particles consist of two protons and two
  neutrons.
• Alpha particles have a 2 charge.
• The symbol for an alpha particle is 42He or a.
• Alpha particles are the most massive of the
  radioactive particles (4 amu), the most damaging,
  and are the least penetrating (easily stopped by
  a piece of paper).

9
What is the product when plutonium-238 undergoes
alpha decay?

• Uranium-234
• Thallium-206
• Lead-206
• Radium-226

10
What is the product when bismuth-210 undergoes
alpha decay?

• Radium-226
• Lead-206
• Thallium-206
• Uranium-232

11
What is the product when polonium-210 undergoes
alpha decay?

• Bismuth-206
• Lead-206
• Radium-206
• Thorium-206

12
Beta Particles

• Beta particles consist of fast moving electrons
  formed by the decomposition of a neutron in an
  atom.
• The neutron decomposes into a proton and an
  electron-the proton remains in the nucleus and
  the electron is emitted.
• Beta particles have a 1- charge.
• The symbol for a beta particle is o-1e or ß.
• Beta particles are 8000 x lighter than an alpha
  particle, are less damaging, but are more
  penetrating (stopped by aluminum foil or thin
  pieces of wood).

13
What is the product when carbon-14 undergoes beta
decay?

• Carbon-13
• Nitrogen-14
• Oxygen-14
• Boron-10

14
What is the product when strontium-90 undergoes
beta decay?

• Rubidium-90
• Krypton-91
• Strontium-91
• Yttrium-90

15
What is the product when potassium-40 undergoes
beta decay?

• Calcium-40
• Scandium-40
• Argon-40
• Chlorine 40

16
Gamma Radiation

• Gamma radiation is high energy electromagnetic
  radiation.
• Gamma rays are emitted along with alpha or beta
  particles.
• Gamma rays have no mass or charge.
• The symbol for gamma rays is oo?
• Gamma rays are extremely penetrating and
  potentially dangerous (stopped only by several
  meters of concrete or several centimeters of
  lead).

17
Other Nuclear Reactions

• Fission-when a large nucleus is bombarded with
  neutrons, a division of the nucleus into 2
  smaller nuclei occurs resulting in a large
  release of energy.
• This energy is used in nuclear power plants and
  in atomic bombs.
• Fusion-nuclei with small masses combine to form a
  nucleus with a larger mass.
• This type of reaction occurs in the sun and in
  hydrogen bombs.
• The high temperature needed to start a fusion
  reaction is produced by a fission reaction.

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Nuclear Decay Puzzle

• Uranium-238 is a radioactive isotope. Through a
  series of 14 nuclear reactions, the unstable
  uranium isotope undergoes radioactive decay until
  it forms a more stable isotope of lead-206.

19
Unstable isotopes formed during the process

• Uranium-234
• Thorium-234
• Thorium-230
• Protactinium-234
• Radium-226
• Radon-222
• Polonium-218

• Polonium-214
• Polonium-210
• Lead-214
• Lead-210
• Bismuth-214
• Bismuth-210

20
Radiation emitted during the process

• Eight alpha particles
• Six beta particles

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Procedure

• Write the isotope symbol for each of the
  radioactive isotopes involved in the problem.
  Put one symbol on each card. (There should be 15
  total)
• On eight cards, write the symbol for alpha
  radiation.
• On six cards, write the symbol for beta
  radiation.
• Put the cards in the correct order to determine
  the steps in going from uranium-238 to lead-206.
• After they are in the correct order, write the 14
  nuclear equations that illustrate the steps.

22
Radioactivity and Half-Lives

• Purpose To simulate the conversion of a
  radioactive isotope over a period of time.
• Data

23
Analysis

• Use graph paper and plot the number of isotopes
  remaining (y-axis) vs. the trial number
  (x-axis).
• Examine your graph. Is the number of isotopes
  remaining over time linear or nonlinear? Is the
  rate constant over time or does it change?
• By approximately how much did the number of
  isotopes remaining decrease with each trial?
• Define half-life. What represented one half-life
  during this lab?

24
Half-Life

• A half-life is the time it takes for one -half of
  the nuclei of a sample of radioactive isotopes to
  undergo radioactive decay.
• Half-lives may be as short as a fraction of a
  second or as long as billions of years.
• For examples, see the chart on page 810.

25
Graph the following data
26
How much remains after 3 days?

• 30 g
• 50 g
• 80 g
• 100 g

27
What is the half life of the isotope?

• 5 days
• 10 days
• 15 days
• 20 days

28
If 25 g remains, how much time has elapsed?

• 5 days
• 10 days
• 15 days
• 20 days

29
How many half-lives have occurred when 25 g
remains?

• 0
• 1
• 2
• 3

30
Determining Half-Lives

• In order to solve problems involving half-lives,
  the following equation may be used
• of half-lives total time/time of one
  half-live
• To determine the amount of sample left, the
  following equation may be used
• amount left starting amount/ 2 of half-lives

31
The half-life of carbon-14 is 5700 years. If a
10 gram sample undergoes decay for 17,100 years,
how many half-lives has the sample undergone?

• 10
• 5
• 3
• 1

32
Cobalt-60 is a radioactive element used as a
source of radiation in the treatment of cancer.
Cobalt-60 has a half-life of five years. If a
hospital starts with a 1000-mg supply, how much
will remain after 10 years?

• 1000 mg
• 750 mg
• 500 mg
• 250 mg

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Homework

• p. 810 pr. 24-25 and p. 829 pr. 73, 74, and 78