Chapter 20: Problem 41
What do each of the following terms mean? (a) thermal neutron, (b) nuclear fission, (c) fissile isotope, (d) nuclear fusion, (e) critical mass
Short Answer
Expert verified
A thermal neutron is a slow-moving neutron in thermal equilibrium with its environment. Nuclear fission involves splitting an atomic nucleus into smaller parts, releasing energy. A fissile isotope is capable of undergoing fission with thermal neutrons. Nuclear fusion is the combining of light nuclei to form heavier ones, releasing energy. Critical mass is the minimum amount of fissile material needed to maintain a self-sustaining chain reaction.
Step by step solution
01
Understanding Thermal Neutron
A thermal neutron is a neutron that has slowed down after being emitted from a fission reaction to reach thermal equilibrium with the surrounding medium. The term 'thermal' suggests that these neutrons have an energy level that is in equilibrium with the temperature of the environment, typically a slow-moving neutron. This is important in nuclear reactors, where thermal neutiles are desired for maintaining a sustained nuclear chain reaction.
02
Defining Nuclear Fission
Nuclear fission is a process where the nucleus of an atom splits into two or more smaller nuclei, along with the release of a significant amount of energy and more neutrons. This process can occur spontaneously in nature or can be initiated in a controlled manner in a nuclear reactor. The energy released during fission is harnessed for power generation in nuclear power plants.
03
Identifying Fissile Isotope
A fissile isotope is a nuclide that is capable of undergoing nuclear fission after capturing a thermal neutron. Not all isotopes are fissile. Fissile isotopes have nuclei that can be split by low-energy (thermal) neutrons which are crucial for sustaining a chain reaction in a nuclear reactor. Examples of fissile isotopes include Uranium-235 and Plutonium-239.
04
Explaining Nuclear Fusion
Nuclear fusion is the process where two light atomic nuclei combine to form a heavier nucleus with the release of energy. Fusion is the process that powers the sun and other stars, where hydrogen nuclei fuse into helium under high temperature and pressure conditions. Fusion releases more energy per unit mass than fission and produces fewer radioactive byproducts.
05
Describing Critical Mass
The term critical mass refers to the minimum amount of fissile material needed to maintain a self-sustaining nuclear chain reaction. Below this mass, the nuclear reaction will die out; above this mass, the reaction can become uncontrolled. The critical mass is dependent on the physical and chemical form of the material, as well as the purity and the presence of neutron moderators/reflector materials.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Thermal Neutron
When we talk about thermal neutrons, we're referring to a specific type of neutron important in the context of nuclear reactions. After a neutron is emitted from a fission reaction, it doesn't just hurtle through space at its original high velocity. Instead, it undergoes what's known as thermalization, a process that slows it down as it collides with other atoms.
These collisions gradually reduce the neutron's energy until it's in line with the ambient temperature of its surroundings – hence the term 'thermal'. It's a bit like a pinball bouncing around and losing momentum with each hit. Why is this important, you ask? Well, in nuclear reactors, we rely on thermal neutiles – these slow-moving neutrons – to sustain a stable nuclear chain reaction, which is fundamental for generating electricity. It's a delicate balancing act; too fast, and they might not trigger further reactions effectively, too slow, and they're captured without contributing to the chain.
These collisions gradually reduce the neutron's energy until it's in line with the ambient temperature of its surroundings – hence the term 'thermal'. It's a bit like a pinball bouncing around and losing momentum with each hit. Why is this important, you ask? Well, in nuclear reactors, we rely on thermal neutiles – these slow-moving neutrons – to sustain a stable nuclear chain reaction, which is fundamental for generating electricity. It's a delicate balancing act; too fast, and they might not trigger further reactions effectively, too slow, and they're captured without contributing to the chain.
Nuclear Fission
Imagine you had a magical candy bar that, when broken in half, gave you not only two pieces of candy but also some extra sweets and a little burst of energy. That's somewhat analogous to nuclear fission. In this process, the nucleus of an atom is split into two or more lighter nuclei. But it doesn't stop there – it also releases a substantial amount of energy and additional neutrons in the split.
The extra neutrons are free to provoke more fissions in other atoms, creating a potential chain reaction of energy release. This cascade is the principle behind nuclear power plants where energy from fission is harvested to generate electricity. It's a process that taps into the very bonds that hold the nucleus together, releasing energy that has been stored since the atom's formation.
The extra neutrons are free to provoke more fissions in other atoms, creating a potential chain reaction of energy release. This cascade is the principle behind nuclear power plants where energy from fission is harvested to generate electricity. It's a process that taps into the very bonds that hold the nucleus together, releasing energy that has been stored since the atom's formation.
Fissile Isotope
While many isotopes exist, not all can throw a party in a nuclear reactor. A fissile isotope is like the life of that nuclear party – it's a nucleus that's got just the right properties to undergo fission when it captures a thermal neutron. These isotopes are the A-listers in the world of nuclear reactions because they have the unique ability to sustain a chain reaction.
Two well-known fissile isotopes that often make headlines are Uranium-235 and Plutonium-239. Fissionable isotopes are key in both the peaceful use of nuclear energy and, unfortunately, in the creation of nuclear weapons. In reactors, they're harnessed to provide a controlled flow of energy – like endless dominos that keep toppling in a designed, manageable way.
Two well-known fissile isotopes that often make headlines are Uranium-235 and Plutonium-239. Fissionable isotopes are key in both the peaceful use of nuclear energy and, unfortunately, in the creation of nuclear weapons. In reactors, they're harnessed to provide a controlled flow of energy – like endless dominos that keep toppling in a designed, manageable way.
Nuclear Fusion
If fission is about breaking apart, then nuclear fusion is all about coming together. Literally. Fusion is the process where two lightweight nuclei merge to form a single, heavier nucleus. The result? A massive release of energy – the same process that lights up the stars and our very own sun.
Compared to fission, fusion is the marathon runner with a higher energy peak and greater endurance. It produces significantly more energy from the same mass of fuel and tends to leave behind fewer radioactive remnants to clean up. Although creating the conditions for fusion on Earth – that is, extremely high pressures and temperatures – is like trying to bottle a star, the quest for controlled fusion continues due to its promise of a cleaner and almost inexhaustible source of energy.
Compared to fission, fusion is the marathon runner with a higher energy peak and greater endurance. It produces significantly more energy from the same mass of fuel and tends to leave behind fewer radioactive remnants to clean up. Although creating the conditions for fusion on Earth – that is, extremely high pressures and temperatures – is like trying to bottle a star, the quest for controlled fusion continues due to its promise of a cleaner and almost inexhaustible source of energy.
Critical Mass
The term critical mass might evoke dramatic Hollywood scenes, but in the world of physics, it's a very specific and less sensational concept. It refers to the smallest amount of fissile material needed to maintain a self-sustaining nuclear chain reaction. Picture a seesaw: too little mass on one side, and the seesaw won't move; too much, and it tips over uncontrollably.
The critical mass for any material depends on its shape, density, purity, and even the environment around the material. Factors like neutron moderators – which slow down neutrons – and reflectors – which bounce them back into the reaction zone – play a role in this delicate balance. The concept of critical mass is not just an academic exercise; it's the key to safety in nuclear power plants and, conversely, to the potential for catastrophe in the case of nuclear weapons.
The critical mass for any material depends on its shape, density, purity, and even the environment around the material. Factors like neutron moderators – which slow down neutrons – and reflectors – which bounce them back into the reaction zone – play a role in this delicate balance. The concept of critical mass is not just an academic exercise; it's the key to safety in nuclear power plants and, conversely, to the potential for catastrophe in the case of nuclear weapons.
