A 2.0 -MeV neutron is emitted in a fission reactor. If it...

Name: Problem 54, Chapter 45: Physics for Scientists and Engineers with Modern Physics
Uploaded: 2020-11-23T13:03:34-08:00
Duration: 2 min 23 s
Channel: Khoobchandra Agrawal
Description: A 2.0 -MeV neutron is emitted in a fission reactor. If it loses half its kinetic energy in each collision with a moderator atom, how many collisions does it undergo as it becomes a thermal neutron, with energy 0.039 eV?

A 2.0 -MeV neutron is emitted in a fission reactor. If it loses half its kinetic energy in each collision with a moderator atom, how many collisions does it undergo as it becomes a thermal neutron, with energy 0.039 eV?

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Key Concepts

Exponential Energy Decay

The repeated loss of a fixed fraction of energy in each collision results in an exponential, or geometric, decay of the neutron's kinetic energy. This mathematical concept allows one to calculate, using logarithmic relations or iterative methods, the number of collisions needed for a neutron to reach a desired energy level.

Thermal Neutrons

Thermal neutrons are neutrons that have been sufficiently slowed down to energies that are in thermal equilibrium with the surrounding environment, typically in the order of fractions of an electronvolt. These low-energy neutrons are particularly effective in sustaining nuclear reactions, such as fission, in a reactor.

Energy Loss in Collisions

When a neutron collides with a moderator atom, it loses a fixed fraction of its kinetic energy. This energy reduction per collision, often modeled as a halving or another constant factor, leads to a series of energy levels that decrease in a predictable geometric sequence.

Neutron Moderation

Neutron moderation is the process by which fast neutrons are slowed down through collisions with light nuclei in a moderator material. This slowing down is crucial in nuclear reactors because it increases the probability of further interactions, such as inducing fission in fuel nuclei.

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