The concentration is high enough to keep neutron multiplication at a minimum.

In this formula, k is the effective neutron multiplication factor, described below.

The counters recorded a neutron multiplication factor of 1.006: the world's first nuclear reactor had gone critical.

On doing so, they discovered significant neutron multiplication in natural uranium, proving that a chain reaction might be possible.

His contributions included determination of the rate of neutron multiplication in heterogeneous uranium-moderator combinations.

Even the inherent statistical fluctuations of neutron multiplication within a chain reaction have implications with regard to implosion speed and symmetry.

The effective neutron multiplication factor, k, is the average number of neutrons from one fission that cause another fission.

Reactivity, in the nuclear engineering sense (not to be confused with chemical reactivity), measures the degree of change in neutron multiplication in a reactor core.

The basic concept of implosion is to use chemical explosives to crush a chunk of fissile material into a critical mass, where neutron multiplication leads to a nuclear chain reaction, releasing a large amount of energy.

By the end of the war, following an idea of Alvin Weinberg, natural uranium fuel elements were arranged in a lattice in ordinary water at the top of the X10 reactor to evaluate the neutron multiplication factor.

In a paper entitled "Critical Conditions on Neutron Multiplication" delivered to the Cambridge Philosophical Society on 14 June 1939, he calculated that it was of the order of tons, too large to make into a practical bomb.

An uncontrolled power excursion occurs due to significantly altering a parameter that affects the neutron multiplication rate of a chain reaction (examples include ejecting a control rod or significantly altering the nuclear characteristics of the moderator, such as by rapid cooling).

Neutron poisons are water-based solutions that contain chemicals that absorb neutrons, such as common household borax, sodium polyborate, boric acid, or gadolinium nitrate, causing a decrease in neutron multiplication, and thus shutting down the reactor without use of the control rods.

Operator error and a faulty shutdown system led to a sudden, massive spike in the neutron multiplication rate, a sudden decrease in the neutron period, and a consequent increase in neutron population; thus, core heat flux increased rapidly beyond the design limits of the reactor.

After nuclear fission was discovered and proved by Otto Hahn and Fritz Strassmann in December 1938, Szilárd and Enrico Fermi in 1939 searched for, and discovered, neutron multiplication in uranium, proving that a nuclear chain reaction by this mechanism was indeed possible.