The mass of fissionable material needed for self sustaining chain reaction is called the:
A. Atomic mass
B. Sub-critical mass
C. Fermi massTATE
D. Critical mass
The Correct Answer and Explanation is:
The correct answer is Critical mass.
Explanation:
In nuclear physics, the term critical mass refers to the minimum amount of fissionable material required to sustain a self-perpetuating nuclear chain reaction. To understand this, it is important to consider how nuclear fission works.
In a nuclear reactor or an atomic bomb, nuclear fission occurs when a heavy nucleus, such as uranium-235 or plutonium-239, absorbs a neutron and becomes unstable. This unstable nucleus splits into smaller nuclei, releasing energy and additional neutrons. These newly released neutrons can then cause further fission reactions in nearby fissionable material, which creates a chain reaction.
However, for the chain reaction to continue and become self-sustaining, a certain amount of fissionable material is required. If there is too little fissionable material, the number of neutrons lost to the surroundings (due to scattering or leakage) will be greater than the number that cause fission reactions, causing the chain reaction to fizzle out. On the other hand, if there is enough fissionable material in a sufficiently compact configuration, the reaction will continue at a steady rate, or even accelerate in the case of an explosion (as in nuclear weapons).
- Critical mass is the minimum amount of fissionable material that allows a chain reaction to become self-sustaining. This mass depends on the specific material being used, its purity, the geometry of the mass, and the presence of any neutron reflectors that can help retain neutrons and promote further reactions.
- Sub-critical mass refers to a mass that is too small to sustain a chain reaction.
- Super-critical mass is when the mass is large enough that the chain reaction accelerates.
- Atomic mass refers to the mass of an individual atom of an element, and the Fermi mass is not a standard term used in this context.
Thus, critical mass is a fundamental concept in the design of nuclear reactors and weapons, as it determines whether the fission chain reaction will sustain itself.