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Chapter 21: Problem 37

Define nuclear fission, nuclear chain reaction, and critical mass.

Short Answer

Expert verified
Nuclear fission is the splitting of a heavy nucleus. A nuclear chain reaction is a self-sustaining fission process. Critical mass is the minimum needed to maintain the chain reaction.

Step by step solution

01

Understanding Nuclear Fission

Nuclear fission is a nuclear reaction in which a heavy nucleus splits into two smaller nuclei along with a few neutrons and a large amount of energy. This process occurs spontaneously in some elements, or it can be induced by the absorption of a neutron.
02

Exploring Nuclear Chain Reaction

A nuclear chain reaction occurs when the neutrons released from a nuclear fission event cause further fission events in nearby nuclei. This process can lead to a self-sustaining sequence of reactions, releasing a substantial amount of energy if uncontrolled.
03

Defining Critical Mass

Critical mass is the minimum amount of fissile material needed to maintain a nuclear chain reaction at a constant rate. If the mass of the fissile material is below this threshold, the reaction will not be self-sustaining.

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Key Concepts

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

Nuclear Chain Reaction
A nuclear chain reaction is an amazing event where one nuclear fission can trigger more reactions. It starts when neutrons released from the splitting of a nucleus hit other nearby nuclei. This impact can make them split too, releasing even more neutrons. As these neutrons go on to strike more nuclei, you get a self-repeating pattern of reactions.
Self-sustaining chain reactions can release massive amounts of energy. This process is what powers both nuclear reactors and atomic bombs.
  • In reactors, these reactions are controlled and used to generate electricity.
  • In bombs, the reactions are uncontrolled, resulting in a tremendous explosion.
Although powerful, chain reactions need careful control. Without moderation, they can become dangerous, leading to potential calamities. That is why understanding and managing them is crucial.
Critical Mass
The concept of critical mass is crucial in nuclear physics. It refers to the smallest amount of fissile material needed to sustain a nuclear chain reaction. If you have a piece of fissile material at this critical mass, the reaction can keep going at a steady pace. If it's too small, called 'subcritical,' the reaction will eventually halt.
Everything changes if you have more than what's needed. Supercritical mass is where the amount exceeds the necessary threshold, leading to a growing, often explosive reaction.
  • Critical mass depends on the type of fissile material.
  • Shape and density also impact the critical mass needed.
  • Reflected neutrons (neutrons bouncing back) can reduce the mass needed for critical mass.
This concept is not just theoretical. It is a key principle that ensures nuclear power is safe and that the safety measures in nuclear weapons are effective.
Fissile Material
Fissile materials are the heroes of nuclear fission. They are special types of atomic nuclei that can easily split when hit by slow-moving neutrons. Uranium-235 and Plutonium-239 are examples of common fissile materials. These nuclei are very sensitive to neutron impacts, making them essential for triggering nuclear fission. In a fission reaction, the choice of fissile material is crucial because it determines how the chain reaction will proceed.
  • Fissile materials are key to both nuclear power generation and nuclear weapons.
  • They must be handled with extreme care due to their potential danger.
  • Different materials have varying levels of efficiency in releasing energy.
An understanding of fissile materials helps us harness their potential in a safe and efficient manner, benefiting energy production while keeping safety a top priority.

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Most popular questions from this chapter

Sources of energy on Earth include fossil fuels. geothermal, gravitational, hydroelectric, nuclear fission, nuclear fusion, solar, and wind. Which of these have a "nuclear origin." either directly or indirectly?

Complete these nuclear equations and identify \(X\) in cach case: (a) \({ }_{12}^{26} \mathrm{Mg}+{ }_{1 \mathrm{P}}^{1} \longrightarrow{ }_{2}^{4} \alpha+\mathrm{X}\) (b) \({ }_{27}^{59} \mathrm{Co}+{ }_{1}^{2} \mathrm{H} \longrightarrow{ }_{27}^{60} \mathrm{Co}+\mathrm{X}\) (c) \({ }^{215} \mathrm{U}+{ }_{0}^{1} \mathrm{n} \longrightarrow{ }_{36}^{94} \mathrm{Kr}+{ }^{139} \mathrm{Ba}+3 \mathrm{X}\) (d) \({ }_{21}^{53} \mathrm{Cr}+{ }_{2}^{4} \alpha \longrightarrow{ }_{0}^{1} \mathrm{n}+\mathrm{X}\) (e) \({ }^{20} \mathrm{O} \longrightarrow{ }^{20} \mathrm{~F}+\mathrm{X}\)

Write complete nuclear equations for these processes: (a) tritium, \({ }^{3} \mathrm{H},\) undergoes \(\beta\) decay; \((\mathrm{b}){ }^{242} \mathrm{Pu}\) under goes \(\alpha\) -particle emission; \((\mathrm{c})^{131} \mathrm{I}\) undergoes \(\beta\) decay: (d) \(^{251}\) Cf emits an \(\alpha\) particle.

A radioactive substance undergoes decay as. \begin{tabular}{cc} Time (days) & Mass (g) \\ \hline 0 & 500 \\ 1 & 389 \\ 2 & 303 \\ 3 & 236 \\ 4 & 184 \\\ 5 & 143 \\ 6 & 112 \end{tabular} Calculate the first-order decay constant and the halflife of the reaction.

Why is it impossible for the isotope \({ }_{2}^{2}\) He to exist?
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