Things unexplained in Oppenheimer

 I KNEW I’D GET MAD WATCHING OPPENHEIMER, because I know Hollywood. They spent much angst along with Oppie, replete with all the worries about the New World it started (20-20 hindsight), managed to insert sex and infidelity, but spent no time on an explanation of the atomic bomb. It’s not hard and here is a quick primer. Radioactive elements have nuclei with elevated states. When they decay they give off a lot of energy and sometimes the nucleus fractures. To make a bomb, you have to have a chain reaction, that is, self-sustaining reaction where one atom’s decay shoots off particles that cause more reactions and constant fission (nucleus splitting) If you can’t figure out how to make this chain reaction, there’s no bomb and no nuclear reactors. Next you have to have enough pure uranium 235, and make a charge that will suddenly implode i.e., bring all the reaction material together for a split second and activate all the reactions in an explosion.

In 1938 2 Germans discovered fission, the splitting of large nuclei, in some radioactive materials, and it was postulated that such a high energy thing could become a powerful bomb. In 1939 Einstein fled Germany and came to USA and wrote FDR about what the Germans were up to. America panicked and virtually demanded that the physicists work on this. The Germans were never able to make a bomb. They achieved no chain reaction, did little enrichment of fissionable material and their scientists like ours were morally nervous about doing this. But a Japanese scientist almost replicated our work, though poorly funded. Enrico Fermi fled Italy as the war started and together with Americans built a pile of Uranium bricks and graphite in secret under an unused Chicago football stadium. This pile keept getting hotter and hotter and proved how to make a chain reaction. Which is tricky. Fission scatters lots of neutrons and since they have no charge, can penetrate almost anything,until they undergo a decay explosion of their own. That means the reactor is dangerous—too much exposure and you’ll die. But the trick is to slow down the neutrons, and this causes the chain reaction to react more. Carbon (graphite) slows neutrons down. Uranium 235 is the reactive atom, but 95% of natural uranium is the inert U238. Refine Uranium oxide out of ore from the Congo. Then you have to separate out the U235, the good stuff. That is what Oak Ridge did with powerful centrifuges and that is what Iran is doing today. Plutonium 239 also reacts, is rare in nature, and can be produced by a nuclear reactor. You build a bomb by jamming enough U235 together in a microsecond and it reacts and explodes. Use a gun-projectile or an implosion method to do this. It was tested at Trinity on a tower near Los Alamos. How much energy? Oppie thought maybe 3 kilotons if they were lucky. It was 20 kilotons. The second atomic bomb hit Nagasaki made of PL239 and was even more powerful.

The film also don’t tell you how Oppenheimer was rich enough to own a big ranch near Albequerque. His family owned 10% of DeBeers diamonds. And being Jewish like Einstein, he was driven to make the idea work before Hitler had a bomb. In fact, Hitler basically cancelled the German project because he couldn’t understand it.