###### Answer: It is the minimum amount of material needed to sustain a fission reaction.

Critical mass – Wikipedia

Critical mass – Wikipedia

Critical mass – Wikipedia

Critical mass (sociodynamics) – Wikipedia

A critical mass is the smallest amount of fissile material needed for a sustained nuclear chain reaction. The critical mass of a fissionable material depends upon its nuclear properties (specifically its nuclear fission cross-section) density shape enrichment purity temperature and surroundings. The concept is important in nuclear weapon design.

When a nuclear chain reaction in a mass of fissile material is self-sustaining the mass is said to be in a critical state in which there is no increase or decrease in power temperature or neutron population. A numerical measure of a critical mass is dependent on the effective neutron multiplication factor k the average number of neutrons released per fission event that go on to cause another fission eve…

When a nuclear chain reaction in a mass of fissile material is self-sustaining the mass is said to be in a critical state in which there is no increase or decrease in power temperature or neutron population. A numerical measure of a critical mass is dependent on the effective neutron multiplication factor k the average number of neutrons released per fission event that go on to cause another fission event rather than being absorbed or leaving the material. When k = 1 the mass is critical and the chain reaction is self-sustaining. A subcritical mass is a mass of fissile material that does not have the ability to sustain a fission chain reaction. A population of neutrons introduced to a subcritical assembly will exponentially decrease. In this case k < 1. A steady rate of spontaneous fissions causes a proportionally steady level of neutron activity. The constant of proportionality increases as k increases. A supercritical mass is one which once fission has started will proceed at an increasing rate. The material may settle into equilibrium (i.e. become critical again) at an elevated temperature/power level or destroy itself. In the case of supercriticality k > 1. Due to spontaneous fission a supercritical mass will undergo a chain reaction. For example a spherical critical mass of pure uranium-235 ( U) with a mass of about 52 kilograms (115 lb) would experience around 15 spontaneous fission events per second. The probability that one such event will cause a chain reacti… Read more on Wikipedia

In social dynamics critical mass is a sufficient number of adopters of a new idea technology or innovation in a social system so that the rate of adoption becomes self-sustaining and creates further growth. The point at which critical mass is achieved is sometimes referred to as a threshold within the threshold model of statistical modeling. The term critical mass is borrowed from nuclear physics and in that field it refers to the amount of a su…

Supercritical carbon dioxide (s CO 2) is a fluid state of carbon dioxide where it is held at or above i…