NUCLEAR REACTIONS

EXPECTATIONS: -- Before we start this unit you should:

  • Understand basic atomic structure including the mass, charge and location of electrons, protons and neutrons

LEARNING GOALS:  At the conclusion of this (mini) unit, students should be able to

1)  demonstrate a basic understanding of nuclear fission:  Heavy elements such as uranium split into smaller atoms and release energy in the process

2)  demonstrate a basic understanding of nuclear fusion:  Lighter elements such as hydrogen combine to form larger atoms such as helium and release energy in the process.

3)  be able to explain to a bright 12 year old that the source of energy in both fission and fusion reactions is a *very* small amount of mass is converted into energy (as shown by E=mc2)

4)  describe in general terms how and why the sun shines.  This is basically fusion (which we call 'nucleosynthesis' when it happens inside a star).

CONCEPTS:

Fission Chain Reaction - The process where a heavy atom such as uranium:

  • absorbs a neutron and becomes *very* unstable
  • splits into two atoms and 2 or more neutrons
  • those neutrons get absorbed by another atom and continue the chain reaction

Fusion Reaction:  Given tremendous temperatures and pressures, hydrogen atoms will smash together to form helium atoms. Some of the mass of the reacting hydrogen is converted into energy.

This is the 'basic' version that I want you to understand:

Several students noted that the mass of the reactants seems to very exactly match the mass of the products. If that troubles you then check out this advanced diagram below:

Note how the first diagram *drastically* simplifies what actually happens as shown by the second diagram (which is definitely beyond the scope of our class)

Nucleosynthesis:  The temperatures (25 million degrees fahrenheit or more) and pressures (billions of times more than the air pressure we experience on Earth) inside stars are high enough so that hydrogen can fuse into helium, helium can fuse into other elements, and othose elements can fuse into yet other elements.  

In simplist terms, nucleosynthesis is fusion inside a star.

(*) The sun converts over 5 million TONS of matter into energy every second.

(*) The sun has 10 x 1 trillion x 1 trillion x 1 trillion nuclear fusion reactions EVERY second!

(*) The sun converts over 5 million TONS of matter into energy every second.

(*) Scientists have very strong evidence to suggest the sun has been doing that since it was 'born' over 5 billion years ago!

Mass into Energy (E=mc2): A key concept in both fission and fusion reactions are that a very, very small amount of mass is converted into energy in each reaction. That is to say that the reactants in each situation have MORE mass than the products of each reaction. The difference is mass is the amount of mass converted into energy.

(*)The most massive nuclear explosion ever detonated by humans converted only a few pounds of mass into energy.

(*) The sun converts over 5 million TONS of matter into energy every second.

(*) The sun has 10 x 1 trillion x 1 trillion x 1 trillion nuclear fusion reactions EVERY second!

VIDEOS:
 The Tsar Bomb -- approximately 2 pounds of hydrogen was converted into helium resulting in a 58 megaton explosion

DOCUMENTS:

►  Mr W Periodic Table

My Black Hen Lays Eggs in the Relative When

She Won't Lay Them Here in the Probably Now

Because

She's Unable to Postulate How