What is the Difference Between Subcritical Critical and Supercritical Mass?

The terms subcritical, critical, and supercritical mass refer to the amount of mass of a fissile material used in nuclear chain reactions. The key difference between these masses lies in their ability to sustain a nuclear chain reaction:

• Subcritical Mass: This is the mass of a fissile material that is insufficient to sustain a nuclear chain reaction. In other words, the material cannot maintain a self-sustaining sequence of fission reactions.
• Critical Mass: This is the smallest amount of fissile material needed for a sustained nuclear chain reaction. At this point, the material can maintain a self-sustaining sequence of fission reactions, but the rate of fission is stable, neither increasing nor decreasing.
• Supercritical Mass: This is the mass of a fissile material that is more than enough to sustain a nuclear chain reaction. When there is a supercritical mass in a system with fission chain reactions, the rate of fission will increase with time, potentially leading to an uncontrolled chain reaction and an explosion. A supercritical mass is also referred to as an exponential growth scenario, where the neutron production increases exponentially over time.

In summary, subcritical mass is too small to sustain a chain reaction, critical mass is just enough to sustain a chain reaction without increasing the rate of fission, and supercritical mass is large enough to cause an increasing rate of fission, potentially leading to an explosion if left uncontrolled.

Comparative Table: Subcritical Critical vs Supercritical Mass

Subcritical, critical, and supercritical mass refer to the amount of mass of a fissile material used in nuclear chain reactions. The key difference between these masses lies in their ability to sustain a chain reaction. Here is a table summarizing their characteristics:

A subcritical mass cannot sustain a chain reaction, as the neutron population exponentially decreases over time. In contrast, a critical mass can sustain a chain reaction, maintaining a steady level of neutron activity. A supercritical mass initially has an increasing rate of fission, but it may settle into equilibrium (become critical again) at an elevated temperature or power level, or it could destroy itself.