Nuclear Weapons Application of Neutron Multiplication
Nuclear fission weapons require a mass of fissile fuel that is prompt supercritical.
For a given mass of fissile material the value of k can be increased by increasing the density. Since the probability per distance traveled for a neutron to collide with a nucleus is proportional to the material density, increasing the density of a fissile material can increase k. This concept is utilized in the implosion method for nuclear weapons. In these devices, the nuclear chain reaction begins after increasing the density of the fissile material with a conventional explosive.
In the gun-type fission weapon two subcritical pieces of fuel are rapidly brought together. The value of k for a combination of two masses is always greater than that of its components. The magnitude of the difference depends on distance, as well as the physical orientation.
The value of k can also be increased by using a neutron reflector surrounding the fissile material
Once the mass of fuel is prompt supercritical, the power increases exponentially. However, the exponential power increase cannot continue for long since k decreases when the amount of fission material that is left decreases (i.e. it is consumed by fissions). Also, the geometry and density are expected to change during detonation since the remaining fission material is torn apart from the explosion.
Read more about this topic: Nuclear Chain Reaction
Famous quotes containing the words nuclear, weapons and/or application:
“Could it not be that just at the moment masculinity has brought us to the brink of nuclear destruction or ecological suicide, women are beginning to rise in response to the Mother’s call to save her planet and create instead the next stage of evolution? Can our revolution mean anything else than the reversion of social and economic control to Her representatives among Womankind, and the resumption of Her worship on the face of the Earth? Do we dare demand less?”
—Jane Alpert (b. 1947)
“I have always been of the mind that in a democracy manners are the only effective weapons against the bowie-knife.”
—James Russell Lowell (1819–91)
“It is known that Whistler when asked how long it took him to paint one of his “nocturnes” answered: “All of my life.” With the same rigor he could have said that all of the centuries that preceded the moment when he painted were necessary. From that correct application of the law of causality it follows that the slightest event presupposes the inconceivable universe and, conversely, that the universe needs even the slightest of events.”
—Jorge Luis Borges (1899–1986)