As the core of main sequence stars hydrogen is fused into helium. Main sequence stars that are much more massive than the sun fuse hydrogen into helium. Then, after the hydrogen is exhausted and the core contracts some, helium is fused into carbon and oxygen – the third and forth most abundant elements in nature.

Please use the table in appendix 10 in RETU for finding the names of the elements, but do not use it in calculations! (this table averages out over various isotopes). Answer the following questions.
 
 

1. When 3 heliums (4.0026 a.m.u) join to make a carbon 12 atom (12.000 a.m.u.), how many atomic mass units are "released" as energy? ________0.0078 a.m.u______

 

 
 
 

2. With 1 atomic mass unit = 1.66 x 10^-27 kg, how much mass in kg is released? _______1.3 x 10^(-29) kg_______

 

 
 
 

3. With E=mc^2, how much energy is released? _1.2 x 10^(-12) Joule___________

 

 
 
 

4. After the helium is exhausted - the core contracts again. Then carbon and oxygen fuse. Carbon with carbon, carbon with oxygen and oxygen with oxygen. When two carbon atoms fuse, what element (23.96 a.m.u) do they form? ____Magnesium (Mg)_

 

 
 
 

5. Is energy released in the process? (Don’t calculate it!) __Yes, because 23.96 < 12.000+12.000__

 

 
 
 

6. When two oxygens fuse, what element (31.96 a.m.u.) do they form? ____Sulfur (S)___

 

 
 
 

7. When an oxygen nucleus fuses with a carbon nucleus they form silicon (27.97 a.m.u.), the most abundant element on our earth. After the carbon and oxygen are exhausted and the core contracts again one possible fusion is of two silicone. In that process 2 protons become neutrons. What is the product of those (55.5 a.m.u.)? Is energy released in this fusion? __Iron (FE). Yes, 55.5 a.m.u. < 27.97 a.m.u. + 27.97 a.m.u_____

 

 
 
 

8. When the fusion of silicon, and other elements of that stage stops, the core contracts again. When the element from 7 fuses with its own kind and an extra proton, and 5 protons become neutrons, what element (112.4 a.m.u.) may they form? ___Cadmium____

 

 
 
 

9. Is energy released in that process? ____No. 112.4 > 55.5+55.5____

 

 
 
 

10. Why is there no energy released in the process? (Remember that the strong "Velcro" force acts over a very short range, whereas the repulsion of positives by positives works over a very long range.) __Energy was released in the previous fusion events because of the strong force pull by protons & neutrons on each other. When we place many protons together ALL OF THEM still push on each other, but only the ones that are "touching" pull each other. Eventually the push by the electric force is larger than the strong-force pull, and we do not gain energy by joining more protons to a larger nucleus._(This is actually the basis for nuclear FISSION of nuclear power stations: you take a large nucleus, say Uranium (238 a.m.u.) and break it into smaller atoms in which the pull by the strong force is stronger than the push by the other protons. In this way energy is GAINED._)

 

 
 
 
 

The element you found in 10 never forms! The element that you found in 7 is the last one to form in the cores of stars!
 
 

11. In the figure below, better known as the "shell model" of nucleosynthesis in heavy stars, fill in the names of elements according to where they are most abundant: Hydrogen in the outer shell, then helium, than carbon and oxygen, then silicone, magnesium and sulfur, then iron.