Fourth Spy Unearthed in U.S. Atomic Bomb Project, Part 3

This is a rare, semi-quiet moment. So let’s finish up the Fourth Spy.

We continue from Fourth Spy Unearthed in U.S. Atomic Bomb Project, Part 2 & Part 1.   Disclaimer: this is not one of the things you need to know, or to start your day. It’s archaeology for entertainment, like digging up a shipwreck.  So I thought of a way to tell the story with the  bonus of understanding some things that are still relevant.

You’ve probably seen Einstein’s famous formula,  , which dates to 1905. In 1938, when the nucleus of the atom was split, a question was posed:

  • An atom splits.
  • The fragments it splits into are known.
  • The mass (weight, to non techies) of all the fragments is known.
  • Some of the mass is missing.
  • Where did the missing mass go?
  • Answer. It was converted to energy as per .

If you weigh yourself clothed, then naked, then

Weight clothed =  weight naked + weight of clothes.

Before  , this would have been expected of an atom and its splits.  But with the atom, some of the weight (mass) is missing. Einstein’s equation explains what happened to it: conversion into energy.

There is a big difference between what physicists call truth, and the popular meaning of the word. There is only one truth that counts: a theory with predictive power. You feed it numbers, it gives you predictions. Nothing else counts. This is in stark contrast with legal truth, religious truth, and common sense.

In the 1930’s,  the atomic nucleus was modeled as a drop of some liquid. The rounded shape of drop of water is caused by surface tension. A drop of water can be split if it is hit by something that makes it spread apart too much for the surface tension to pull it back. Lise Meitner and Otto Frisch used this to explain fission.

An atomic nucleus can split in many ways. For each kind of split, the drop model accurately predicted the energy release for that split. But it could not predict how it would split.  How does the cookie crumble? A physics “truth” that would predict how the atom crumbles would not come until the 1950’s.  But the Manhattan Project had to know now.

The Manhattan Project was the extreme of front-loading. 95.3% of the money was spent by gigantic industrial combines producing materials for a bomb. At Los Alamos, where only 4.7% of the money was spent, they didn’t know how to make a bomb. Imagine a contract for the F-35 fighter let before the Wright Brothers first powered flight in 1903. The Manhattan project was saved from ignominy by the fact that it worked.

Initially, the combines produced mere traces, then grams, of purified uranium-235, and plutonium.  The kilograms mass of plutonium metal required by the Bomb became available only a few weeks before the Trinity test, in July 1945. How can you experiment with bomb-making without explosive?

The Los Alamos teams spent their first two years, figuring out:

  1. the amount of uranium or plutonium which have to be assembled to produce critical mass, and for how long.
  2. that the gun-type bomb would work for one particular fuel, uranium-235, and not for plutonium.
  3.  how to compress (implode) a “pit”, the critical mass of plutonium, using John von Neumann’s solutions of the Taylor shock wave equations, to design shaped charges, detonators, and power supplies.
  4. the design of the “initiator”, which was then a special radioactive mass at the center of the pit.
  5.  how an explosively critical mass would  behave in the few microseconds of its existence. What was the interval of time nicknamed the “shake”. How many shakes did it take to make the bang?
  6. that a lot of potential designs and shortcuts were dead ends.
  7. the various ways uranium splits, testing the nuclear drop model, with an ingenious device, the “water boiler reactor.” Finding critical mass with different water-based solutions was considered valuable exercise, since there wasn’t enough bomb-grade uranium until 1945 to experiment with solid metal.

With which of the above activities were Godsend’s E.E. based skill set and job experience useful?

  • Exclusion of 1 and 2. This is physics, not E.E. Those who worked on it are in the record.
  • Exclusion of 3. The design of the implosion mechanism required some electrical design, but unrelated to Godsend’s specialty. He had expertise with Calutrons and mass spectrometers, which elevated him above the basic B.S., but only for this specialization. There were people with more applicable background, who appear in the record.
  • Exclusion of 4.  This is pure physics.
  • Exclusion of 5.  It is now known that the nuclear chain reaction occurs on a “cycle”, or generations, measured in “shakes.”  A shake is a 10 billionths of a second. Before the invention of the Esaki tunnel diode in 1957, electronics couldn’t deal with tiny time.  In a modern lab, a contemporary Godsend could fit in. This also applies to 1.
  • Exclusion of 6.  Godsend was not a manager.

This leaves 7. In the finale, we’ll see how Godsend stole Los Alamos’s mojo.

 

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