LECTURE                                              FUSION

In this lecture you will learn:

FUSION: THE POWER OF THE SUN
e+ = positron or positive electron 
v = photon (energy, like photon torpedoes on Star Trek)
a proton and a photon are not the same things!

The fusion of hydrogen to helium needs 4 hydrogens

1. 2 hydrogen PROTONS are fused. 

2. A positron (e+) leaves one of the protons which converts a proton into a neutron. This is still hydrogen but called deuterium, heavy water, 1N, 1P. 

3. The deuterium is then fused with another proton to make a helium, 1N, 2P but it is deficient by one neutron and is called 3He 

4. Two 3He fuse to make (1) 4He (2N, 2P) and two protons are released (2 H). 
 


EXCELLENT EXPLANATION
http://hyperphysics.phy-astr.gsu.edu/Hbase/astro/procyc.html
SUMMARY 
reactants description product 
H+ and H+ two hydrogens are fused
a positron (e+) is lost leaving a neutron
2H (deuterium)
positron e+
2H and H+ deuterium is fused with another proton 
helium deficient in neutron
3He
3He + 3He two 3He fuse, 2 protons leave 4He, 2 H+ and energy

 
FUSION AND FISSION: THE MASS DEFECT
Scientists noticed that when the hydrogens were fused to make helium the  resulting mass of protons and neutrons in helium were smaller than the sum of the hydrogen nuclei that went into making the helium.  This is called THE MASS DEFECT

The decrease in mass is not lost, it is converted to energy and

1. part is used to bind the nuclei together (those pesky protons with their positive charge) (the strong force) and

2. some is released ... that is the energy spewing out of the sun and fueling life on earth
 
 

 

MORE ON THE MASS DEFECT - the graph on the right

Helium + other nuclei are fused to make elements higher up the periodic table until iron is reached. Until iron the nuclei LOSE mass which is converted into energy.  The fusion of hydrogen yields the most energy. 

Once iron is reached the mass of the fusion products begins to increase  so an input of energy is required to form the extra mass. 

The nuclei of elements that are naturally radioactive or that can be made to be radioactive can split or lose protons and neutrons and they give up energy as a result, this is fission.  The amount of energy is small compared to fusion. 

In Einstein's theory of relativity, mass and energy are the same thing, they are just different forms. E=MC*2 is the relationship between them. 


 
WHERE DOES THE ENERGY COME FROM? WHERE DID ALL THE HEAVIER ELEMENTS COME FROM?
where do we find enough energy to fuse the nuclei of smaller elements, adding enough energy to make heavier elements? In stars!!!
- not our star, the sun. In the core of our sun, hydrogen is fusing to helium, and someday to carbon, but then our star will collapse and die. It will never even get around to making iron.
 
Only in the really large massive stars is there enough mass to sequentially make the fusions up to iron.  Then, when iron starts fusing, it must suck up energy to make the larger nuclei (the mass defect), and this cools the enormous star.  So when the core starts cooling, it collapses in tremendous shock waves that results in the star exploding. This is a supernova.

A supernova is the violent explosion and shock waves that forces nuclei to fuse into the elements iron and larger. It happens within a very short time span. These elements are blown out into the galaxy where they will eventually begin coalescing (mass attraction) to form other suns, and planets and solar systems 

SO ALL OF US HAVE WITHIN US THE MATERIAL OF STARS AND SUPERNOVA.

REVIEW QUESTIONS:

Compare fusion and fission.
Describe the relative amounts of energy released by fusion vs fission. Draw the curve.
Discuss where and how all the heavier elements come from and are formed?
Discuss how our Sun provides the Earth with energy.
Fusion occurs until what element is reached?
FUSION
Hydrogen fusion
PLASMA
The mass of protons and neutrons are larger in hydrogen nuclei than in helium nuclei.  What happens to the lost mass?
What are two origins of energy in the universe?
What are the two main sources of heat on Earth?
What holds protons together?
What is the source of energy in fusion?
What is fusion?
What is the mass defect?
What happens in massive stars when iron starts fusing?
What causes a supernova?
What is plasma? What conditions are necessary for fusion to occur? What part of the atom is not present in plasma?
What part of the atom is involved in fusion?
Where does the energy of mass defect go?