The sum of all fears - Tom Clancy [367]
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.
For several more nanoseconds, this did not matter.
The plutonium was still increasing its reaction rate, still doubling, still increasing its Alpha at a rate only expressible numerically.
Energy was now flooding into the Secondary. The metallically-coated straws flashed to plasma, pressing inward on the Secondary. Radiant energy in quantities not found on the surface of the sun vaporized but also reflected off elliptical surfaces, delivering yet more energy to the Secondary assembly, called the Holraum. The plasma from the immolated straws pounded inward towards the second reservoir of lithium compounds. The dense uranium 238 fins just outside the Secondary pit also flashed to dense plasma, driving inward through the vacuum, then striking and compressing the tubular containment of more 238U around the central container which held the largest quantity of lithium-deuteride/tritium. The forces were immense, and the structure was pounded with a degree of pressure greater than that of a healthy stellar core.
But not enough.
The Primary's reaction had already slackened. Starved of neutrons by the presence of the 3He poison, the bomb's explosive force began to blow apart the reaction mass as soon as the physical forces reached their balance. The chain reaction reached a moment of stability, at last unable to sustain its geometric rate of growth; the last two chain-reaction doublings were lost entirely, and what should have been a total Primary yield of seventy thousand tons of TNT was halved, halved again, and in fact ended with a total yield of eleven thousand two hundred tons of high explosive.
Fromm's design had been as perfect as the circumstances and