The sum of all fears - Tom Clancy [366]
Ordinarily denser than lead, the plutonium was compressed further by the million-atmospheres pressure of the implosion. This had to be done very quickly. The plutonium 239 mass also included a small but troublesome quantity of plutonium 240, which was even less stable and prone to pre-ignition. The outer and inner surfaces were slammed together and driven in turn towards the geometric center of the weapon.
The final external act came from a device called a 'zipper.' Operating off the third signal from the still-intact electronic timer, the zipper was a miniature particle accelerator, a very compact mini-cyclotron that looked remarkably like a hand-held hair-dryer. This fired deuterium atoms at a beryllium target. Neutrons traveling ten percent of the speed of light were generated in vast numbers and traveled down a metal tube into the center of the Primary, called the Pit. The neutrons were timed to arrive just as the plutonium reached half of its peak density.
Ordinarily, a material weighing roughly twice an equivalent mass of lead, the plutonium was already ten times denser than that and still accelerating inward. The bombardment of neutrons entered a mass of still-compressing plutonium.
Fission.
The plutonium atom has an atomic weight of 239, that being the combined number of neutrons and protons in the atomic nucleus. What began happened at literally millions of places at once, but each event was precisely the same. An invading 'slow' neutron passed close enough to a plutonium nucleus to fall under the Strong Nuclear Force that holds atomic nuclei together. The neutron was pulled into the atom's center, changing the energy state of the host nucleus and kicking it into an unstable state. The once symmetrical atomic nucleus began gyrating wildly and was torn apart by force fluctuations. In most cases a neutron or proton disappeared entirely, converted to energy in homage to Einstein's law E = MC^2. The energy that resulted from the disappearance of the particles was released in the form of gamma and X-radiation, or any of thirty or so other but less important routes. Finally, the atomic nucleus released two or three additional neutrons. This was the important part. The process that had required only one neutron to start released two or three more, each traveling at over 10 percent of the speed of light - 20,000 miles per second - through space occupied by a plutonium mass two hundred times the density of water. The majority of the newly-liberated atomic particles found targets to hit.
A chain-reaction merely means that the process builds on itself, that the energy released is sufficient to continue the process without outside assistance. The fission of the plutonium proceeded in steps called 'doublings.' The energy liberated by each step was double that of the preceding one, and that of each subsequent step was doubled again. What began as a trivial amount of energy and just a handful of freed particles doubled and redoubled, and the interval between steps was measured in fractions of nanoseconds. The rate of increase - that is, the acceleration of the chain reaction - is called the 'Alpha,' and is the most important variable in the fission process. An Alpha of 1,000 means that the number of doublings per microsecond is a vast number, 2^1000 - the number 2 multiplied by itself one thousand times. At peak fission - between 2^50 and 2^53 - the bomb would be generating 10 billion billion watts of power, one hundred thousand times the electrical-generating capacity of the entire world. Fromm had designed the bomb to do just that - and that was only ten percent of the weapon's total designed output. The Secondary had yet to be affected. No part of it had yet been touched by the forces only a few inches away.
But the fission process had scarcely begun.
Some of