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 the gamma rays, traveling at the speed of light, were outside the bomb case while the plutonium was still being compressed by the explosives. Even nuclear reactions take time. Other gamma rays started to impact on the Secondary. The majority of the gammas streaked through a gas cloud that only a few microseconds earlier had been the chemical explosive blocks, heating it far beyond the temperatures chemicals alone could achieve. Made up of very light atoms like carbon and oxygen, this cloud emitted a vast quantity of low-frequency 'soft' X-rays. To this point, the device was functioning exactly as Fromm and Ghosn had planned.

The fission process was seven nanoseconds - 0.7 shakes - old when something went wrong.

Radiation from the fissioning plutonium blazed in on the tritium-impregnated lithium-deuteride that occupied the geometric center of the Pit. The reason Manfred Fromm had left the tritium extraction to last lay in his basic engineer's conservatism. Tritium is an unstable gas, with a half-life of 12.3 years, meaning that a quantity of pure tritium will, after that time, be composed half of tritium and half of 3He. Called 'helium-three' 3He is a form of that second-lightest of elements whose nucleus lacks an extra neutron, and craves another. By filtering the gas through a thin block of palladium, the 3He would have been easily separated out, but Ghosn hadn't known about that. As a result, more than a fifth of the tritium was the wrong material. It could hardly have been a worse material.

The intense bombardment from the adjacent fission reaction seared the lithium compound. Normally a material half the density of salt, it was compressed to a metallic state that exceeded the density of the earth's core. What began was actually a fusion reaction, though a small one, releasing huge quantities of new neutrons, and also changing many of the lithium atoms into more tritium, which broke down - 'fused' - under the intense pressure to release yet more neutrons. The additional neutrons generated were supposed to invade the plutonium mass, boosting the Alpha and causing at least a doubling of the weapon's unboosted fission yield. This had been the first method of increasing the power of the second-generation nuclear weapons. But the presence of 3He poisoned the reaction, trapping nearly a quarter of the high-energy neutrons in uselessly stable helium atoms.