Question

2) Write at least one paragraph to discuss how plasma forms at the core of a star. Be sure to include the definition of plasma and why the conditions are able to sustain fusion here.

3) Use the search engine of your choice to find the temperature at which hydrogen fusion takes place. Also find the temperature at which helium fusion takes place. Which one is higher, and by what factor? Discuss your interpretation of why one of the processes requires such a higher temperature.

4) The process of helium fusion is known as the triple alpha process. How many steps are there in this process? What are they? What element is the result of helium fusion? Does this surprise you? If so, why?

5) Notice that lithium, beryllium, and boron are not produced in mass quantities like helium and carbon? Why do you think this is? Are they produced at all in stars?

6) The proton-proton chain and the triple alpha process are both exothermic. It turns out that all fusion processes that result in an element between hydrogen (1 proton) and iron (26 protons) are exothermic. Why is this important? What would make it difficult for an endothermic fusion process to be sustained?

7) Finally, iron is the most tightly bound nucleus. This means that it has the least average mass per nucleon (protons and neutrons). Another way to think about this is using something called the binding energy. Iron also has the largest binding energy per nucleon. This means that as the binding energy per nucleon increases from hydrogen to iron the fusion processes are exothermic. Once elements heavier than iron begin to fuse then the binding energy per nucleon decreases and the fusion processes become endothermic. Why do you think this happens

Answer 1

2. Imagine an enormous cloud of gas and dust many light-years across. Gravity, as it always does, tries to pull the materials together. A few grains of dust collect a few more, then a few more, then more still. Eventually, enough gas and dust has been collected into a giant ball that, at the center of the ball, the temperature (from all the gas and dust bumping into each other under the great pressure of the surrounding material) reaches 15 million degrees or so. nuclear fusion begins and the ball of gas and dust starts to glow. As the contraction of the gas and dust progresses and the temperature reaches 15 million degrees or so, the pressure at the center of the ball becomes enormous. The electrons are stripped off of their parent atoms, creating a plasma. The contraction continues and the nuclei in the plasma start moving faster and faster. Eventually, they approach each other so fast that they overcome the electrical repulsion that exists between their protons. The nuclei crash into each other so hard that they stick together, or fuse. In doing so, they give off a great deal of energy. This energy from fusion pours out from the core, setting up an outward pressure in the gas around it that balances the inward pull of gravity. When the released energy reaches the outer layers of the ball of gas and dust, it moves off into space in the form of electromagnetic radiation. The ball, now a star, begins to shine.

3. From google, hydrogen fusion occurs at 13 million K

He fusion takes place at 100 million K

hence He fusion requires about 8 times as much temperature as Hydrogen fusion

As He atom has two protions hence He fusion requires more energy than H fusion

4. For triple alpha process

4 He 2 + 4 He 2 - > 8 Be 4

8 Be 4 + 4 He 2 - > 12 C 6 + 2 *gamma + 7.367 MeV

hnce there are two steps

final result is 12 C

5. Li, Be and B are not produced in mass quantities as compared to He and C because of relative stability of the Nucleii of C and He atoms.