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Chapter 14: Problem 20

On Earth, nuclear power plants use \(f\) ission to generate electricity. In fission, a heavy element like uranium is broken into many atoms, where the total mass of the fragments is less than that of the original atom. Explain why fission could not be powering the Sun today.

Short Answer

Expert verified
The Sun uses fusion, not fission, to produce energy because it mainly consists of hydrogen and very little heavy elements like uranium.

Step by step solution

01

- Understand Fission

Fission is a nuclear reaction where a heavy nucleus, like uranium, splits into smaller nuclei, releasing energy in the process. This is commonly used in nuclear power plants on Earth to generate electricity.
02

- Examine the Sun's Energy Source

The Sun's energy comes from nuclear fusion, not fission. In fusion, light elements like hydrogen combine to form heavier elements like helium, releasing vast amounts of energy.
03

- Compare Fission and Fusion

Fission involves splitting heavy elements, which would require the Sun to have a large supply of heavy elements like uranium. Fusion, on the other hand, utilizes hydrogen, which is abundantly available in the Sun.
04

- Analyze Elemental Abundance

The Sun primarily consists of hydrogen and helium, with very little heavy elements like uranium. Therefore, fission cannot sustain the Sun's energy output as there isn't enough heavy elements to support this process.
05

- Energy Release Comparison

Fusion reactions release more energy per unit mass compared to fission reactions. Given the massive energy output of the Sun, fusion is the only viable process to maintain such high energy levels.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

nuclear fission
Nuclear fission is a process where a heavy atomic nucleus, such as uranium or plutonium, splits into smaller nuclei. This splitting releases a significant amount of energy.
In nuclear power plants, this energy is harnessed to produce electricity. When the nucleus splits, it also releases neutrons, which can trigger further fission reactions. This chain reaction is what keeps the process going, producing steady energy for power generation.
However, fission requires heavy elements like uranium, which are not abundant in the Sun. The Sun mainly contains hydrogen and helium, making fission an unsuitable energy source for the Sun.
nuclear fusion
Nuclear fusion is the process that powers the Sun. In fusion, two light atomic nuclei come together to form a heavier nucleus. For example, hydrogen nuclei (protons) fuse to form helium.
This process releases a tremendous amount of energy. Fusion requires extremely high temperatures and pressures to overcome the repulsive forces between the positively charged nuclei.
In the Sun's core, temperatures reach about 15 million degrees Celsius, providing the necessary conditions for fusion. Since the Sun is abundant in hydrogen, it can sustain fusion reactions over billions of years, continuously radiating energy.
elemental abundance
The Sun's composition is predominantly hydrogen (about 75%) and helium (about 24%). Other elements, such as oxygen, carbon, and neon, make up less than 2% of the Sun's mass.
This high abundance of hydrogen makes fusion the ideal process for the Sun's energy production. Fusion relies on hydrogen nuclei combining to form helium, which matches the Sun's elemental makeup.
On the other hand, heavy elements necessary for fission, like uranium, are extremely scarce in the Sun. This scarcity makes fission an impractical source of the Sun’s immense energy output.
energy release
Both nuclear fission and fusion release energy, but the amount varies significantly. Fusion releases many times more energy per unit mass than fission.
The Sun's energy results from the fusion of hydrogen into helium. For instance, fusing four protons to form one helium nucleus releases 26.7 MeV (million electron volts) of energy.
In comparison, fission of a uranium nucleus releases about 200 MeV of energy. While this might seem large, considering the Sun's composition and energy needs, fusion's greater efficiency makes it the dominant process.
helium and hydrogen
Hydrogen and helium are the two most abundant elements in the Sun. Hydrogen is the lightest and most plentiful element in the universe, making it the primary fuel for fusion reactions.
When hydrogen nuclei fuse, they form helium, the second lightest element. This fusion process releases vast amounts of energy, which we receive as sunlight.
The continuous conversion of hydrogen to helium in the Sun's core has sustained the star for about 4.6 billion years and will continue to do so for billions more. This process ensures the Sun remains a reliable energy source for our solar system.

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Most popular questions from this chapter

In the proton-proton chain, four hydrogen nuclei are converted to a helium nucleus. This does not happen spontaneously on Earth because the process requires a. vast amounts of hydrogen. b. very high temperatures and densities. c. hydrostatic equilibrium. d. very strong magnetic fields.

The hydrogen bomb represents an effort to create a similar process to what takes place in the core of the Sun. The energy released by a 5-megaton hydrogen bomb is \(2 \times 10^{16} \mathrm{J}\) a. This textbook, \(21^{\text {th }}\) Century Astronomy, has a mass of about 1.6 kg. If all of its mass were converted into energy, how many 5 -megaton bombs would it take to equal that energy? b. How much mass did Earth lose each time a 5-megaton hydrogen bomb was exploded?

In the proton-proton chain, the mass of four protons is slightly greater than the mass of a helium nucleus. Explain what happens to this "lost" mass.

Energy is produced primarily in the center of the Sun because a. the strong nuclear force is too weak elsewhere. b. that's where neutrinos are created. c. that's where most of the helium is. d. the outer parts have lower temperatures and densities.

The Sun has a radius equal to about 2.3 light-seconds. Explain why a gamma ray produced in the Sun's core does not emerge from the Sun's surface 2.3 seconds later.
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