The "A" Bomb

Growing up in the 50’s was the best, but it was not without it’s threats. I remember being terrified of catching Polio before Dr. Salk came out with his vaccine, and who could forget the “drop and cover” exercises in the classroom, or the backyard bomb shelters being sold as protection from Russian nuclear attack? I actually know people who had them. The development of nuclear weapons is an interesting sequence of events and I only understand it superficially, but I would like to try to explain it here.

Physics is simply the study of the relationship between the basic laws of the universe that govern gravity, momentum, inertia, etc. The first one we learn in school, and the one most of us probably remember is “for every action there is an equal and opposite reaction.”

I know most of us have heard or seen the formula that represents Einstein’s theory of relativity, E=MC2 (the 2 means "squared" but this editing program does not support superscript) but have you ever wondered about it’s application or what it means? On its face it is a very simple algebraic expression, like A=B times C. In Einstein’s formula, E is “Energy,” “M,” is mass, and “C” is the universal constant, the speed of light, which is 186,000 miles/second (300,000 kilometers/sec). Notice that Einstein’s famous formula uses C2, which is C multiplied by C or 186,000 X 186,000 or 34,596,000,000, quite a large number.

In the early days of experimentation with splitting atoms (nuclear fission), they used a thing called a cloud chamber to watch the effects. A cloud chamber was nothing more than an enclosure filled with gas or liquid. When an atom is split inside a cloud chamber the separate particles produce vapor trails, much like jet aircraft do at high altitudes. Applying an external magnetic field to the particles in the cloud chamber caused the paths of the vapor trails (particles) to arc, and by measuring the arc and applying the laws of physics, the mass of the particles resulting from fission could be accurately determined. In this way, scientists discovered that the mass of all the resulting particles did not equal the mass of the original atom. Where did the missing mass go? It was converted to pure radiated energy, in the form of heat and light. How much energy was released? This is where it gets interesting.

When the simple formula E=MC2 is applied and you multiply the very small amount of mass lost during fission by the very large number C2, you end up with a very sizeable amount of energy released. Now all you have to do to create a bomb is to split many, many atoms at about the same time. Enter, the chain reaction! It took a lot of energy to split even a single atom, and the pieces produced did not have the energy needed to strike and split adjacent atoms. What was needed was a material that was already unstable and ready to fall apart on its own, and they found it in Uranium 235. They found a way to refine and manipulate the structure of Uranium 235 so that it was very, very unstable. In this form, the splitting of one of the atoms would send the ensuing pieces flying into other, nearby, atoms and cause them to split and you have a chain reaction that is limited only by the amount of material available! Each one, of billions of atoms, splitting and releasing energy in the form of heat and light, voila’, a bomb!

The actual story of the development of atomic bombs, the “Manhattan Project” is much more interesting and delves into the effort it took to refine the Uranium 235 to “weapons grade” (a story in itself) and the further effort it took to devise a method to, on demand, set off the initial atom split. By the way, the word is pronounced like new-clear, not new-Q-lar, as ex-president bush would have us believe.