A Fissionable Christmas: Part Two
By Justin Isherwood
In the history of science, insight comes at odd times and odd places, in this case Frisch and Meitner were skiing, actually Frisch was skiing, Meitner was walking behind as they talked in a relaxed mood, rolling in their minds these strange nuclear particles. The physics is a mental thing, in the hope of imagining what is going on inside the smallest bit of matter. They were, as they later reported, turning this nuclear thing in their heads. Hahn, in an experiment targeting uranium, ended up with material identified as barium. How was that possible? Barium being a metal in the middle of the Periodic Chart Group 2 , Period 6, Block S, atomic weight 56. This nuclear physics stuff, Jewish or not, was weird. It was Christmas, 1939.
It was Frisch on his skis who burst out,” there’s no other explanation.” He paused as the vapors of his exertion disappeared into the winter air. That damnable strangeness of uranium turning into barium overwhelmed their minds. Why? Here this Christmas Story unfolds as Lise Meitner later recalled. They brushed away the snow on a nearby log, sat down and on a scrap of paper calculated the initial charge of a uranium nucleus, and what the energy necessary to overcome the surface tension, as they called it, to divide the uranium nucleus. The “provocation” by which they meant the impact of a single neutron, where elemental uranium divides to lighter elements. The barium in the middle of the Periodic Chart, as a fraction of its mass disappears. The business quite as Einstein put it, E=mc2.. One fifth of a proton mass equals 200 MeV in mass to energy conversion. In halving a uranium atom, two barium atoms form along with “some energy.” Again their phrase, “some energy.”
Was Christmas 1939, as this hypothesis sifted through the physics world, and in the following new year, a few began to postulate this energy as “a bomb source.” The idea was generally, even enthusiastically, poo-pooed. A bomb would require tons of U-238, and the reaction could not be sustained.
Others worried, what if the Nazis suspected? Then came news Germany was forbidding export of uranium from Czechoslovakia. It was more than just a possibility the Nazis knew of the bomb chance.
Niels Bohr and John Wheeler dissed the idea U-238 would work as a bomb source, if U-235 would. Other than the stuff being a touch scarce, about 0.7% of uranium ore. Their hypothesis posed a pound of U-235 would be necessary to make an atomic bomb. As it turned out, closer to 35 pounds. Little Boy, over-built, was 141 pounds of U-235.
Otto Frisch soon delivered the world to its fate and his method for separating 235 from 238. Quite simple really. Fill a tube with a U-238 gas, the heavier U-238 to sink leaving the lighter, fissionable U-235 to siphon off. A pound of U-235 by this process could be produced in matter of weeks. The estimate turned out a touch optimistic. American juggernaut of 1941-1945, from Manhattan to Oak Ridge to Los Alamos was the largest construction project in human history, all of it devised to yield a device the size of a large office desk called Little Boy. Where but 2 pounds of Uranium 235 was converted to energy of the 141 pounds “in the pit,” at 8 kilotons per pound.
The Los Alamos bomb test was named Trinity, following John Donne’s poem. Appropriate, as when the gods of the universe become one, the prophesy is, the world ends.
Such were the words on the range that fateful morning of 10 July, 1945,: “unprecedented”, “magnificent”, “beautiful”, “stupendous”, “terrifying..”
And so the Christmas star of Lise Meitner and its Jewish science rose above the New Mexico desert. In its new dawn came a new age of man, kind or not.