Thermonuclear Fusion (Part 2)

Historical Context

  • Great Antiquity of Earth and Sun

    • Early views held the Earth was a few thousand years old.

    • Bishop James Ussher calculated the creation date to be 4004 BC, leading to a widely accepted age of 6000 years.

    • Victorian scientists assumed the Sun's energy came from chemical combustion, estimating its age at 10,000 years.

Evolution of Understanding

  • Geological and Biological Sciences Advancement

    • Late 19th century saw significant evolution in biology and geology that questioned the age estimates of 10,000 years.

    • Longer timescales were needed for geological and biological evolution processes.

  • Lord Kelvin's Contribution

    • In 1846, Kelvin believed the Earth and Sun were created simultaneously.

    • He calculated the cooling period of Earth from the Sun's temperature resulting in 100 million years, asserting the Earth could be no older.

    • This caused outrage among geologists who had established longer timeframes, and his miscalculation affected the reputation of natural sciences for decades.

Discovery of the Nuclear Energy Source

  • Energy Source Mystery until WWII

    • The origin of energy for the Sun and stars remained unresolved until just before World War II.

    • The nuclear model of the atom, established by Ernest Rutherford, revealed atomic structure.

Atomic Structure

  • Properties of Atoms

    • Atoms contain a small nucleus with positive charge and mass.

    • A cloud of negatively charged electrons orbits the nucleus balancing the positive charges.

Scale of Atoms

  • Atom vs. Nucleus Size

    • The size of an atom is approximately 10810^8 times the diameter of its nucleus.

    • Example: If a pea (~ 1/2 cm) represents a nucleus, the atom's outer extent would reach 50 km away, for example, from Guelph to Hamilton.

Representation of Atoms

  • Lithium Atom Example

    • Depicted on a Spanish stamp honoring Wilhelm Roentgen.

    • Central nucleus surrounded by three orbiting electrons.

    • The three electrons dictate the chemical properties of lithium, leading to isotopes with varying atomic masses: 6Li (3 protons, 3 neutrons) and 7Li (3 protons, 4 neutrons).

  • Hydrogen and Helium

    • Hydrogen (1 electron):

    • Isotopes include 1H (no neutrons), 2H (1 neutron), and 3H (2 neutrons).

    • Helium (2 electrons):

    • Isotopes include 3He and 4He.

Summary of Subatomic Particles

Name

Symbol

Mass

Electric Charge

Electron

e

0 (approx.)

-1

Positron

e+

0 (approx.)

+1

Proton

p

1

+1

Neutron

n

1

0

Neutrino

n

0 (nearly massless)

0

Gamma ray

g

0

0

Additional Entities in Nuclear Reactions

  • Electron (e):

    • Exists in two forms:

      • Negatively charged electron (e-) that forms atom volume.

      • Positron (e+), produced in high-energy reactions; annihilates with an electron to produce gamma rays (g).

  • Neutrino (n):

    • Nearly massless particle with no electric charge, generated in nuclear reactions.

  • Gamma Rays (g):

    • High-energy electromagnetic waves analogous to light rays, significant in nuclear physics.