THE ABC'S OF NUCLEAR BOMBS

In the current state of the world, it might be helpful to know this stuff.

Peter Sellers as Dr. Strangelove and Slim Pickens as Air Force Major T.J. "King" Kong in Stanley Kubrick's 1964 classic "Dr. Strangelove or: How I Learned to Stop Worrying and Love the Bomb"

Last month's biggest news story was hard to miss-- the U.S. President sent Air Force B-2 bombers armed with "bunker-buster" bombs to blow up Iran's deep-underground Uranium enrichment facility, thereby (ostensibly, anyway) preventing the current leaders of the erstwhile Persian Empire from producing a nuclear bomb in the foreseeable future.

And what, exactly, is a "nuclear bomb?" The short answer? The most powerful and destructive military armament ever devised by mankind, one that owes its explosive power to a nuclear reaction. For the long answer (and some Grumpy Old Mansplaining on steroids) we start with some basic chemistry and physics--

Atoms are the basic building blocks of matter. The Bohr Model (circa 1915) is a simplistic yet useful representation of atoms, composed of three different particles-- protons, neutrons, and electrons.

In Dr. Niels Bohr's model shown above, the turquoise-colored things with the minus signs are electrons, which are negatively charged and determine an atom's outward chemical characteristics such as the propensity to burn, or dissolve in water, or combine with other atoms to form molecules (a.k.a. compounds) that behave much differently than do their individual components. (Highly flammable sodium atoms, for instance, link up with deadly poisonous chlorine atoms to form sodium chloride, or table salt.) Noteworthy for our purposes here is the molecule trinitrotoluene, more familiarly by the initials TNT-- a combination of carbon, hydrogen, oxygen, and nitrogen atoms that violently explodes as it breaks down into smaller components... an extreme example of a chemical reaction.

While TNT and other "conventional" explosives owe their destructiveness to chemical reactions, i.e., interactions involving electrons, nuclear bombs owe their horrible power to reactions involving not electrons but rather the black and white things in the atom's inner circle-- the nucleus. The negative charge of the each electron is offset by one of the black things, a positively-charged proton. The white things are neutrons, which have no electrical charge and weigh approximately the same as protons-- both much heavier than electrons. Protons and neutrons are tightly bound in the nucleus by attractive forces powerful enough to overcome the electrostatic repulsion from the positive electrical charges of the protons. (Think of magnets that try repel each other but can nonetheless be held together in one's hand.)

My favorite physics teacher liked to say that if you think you understand nuclear physics, you really don't, because it makes no logical sense in the context of our real-world experiences. These powerful binding forces between nuclear particles, for instance, somehow contribute to the actual mass of a nucleus. And so unlike chemical reactions, nuclear reactions can result in a small amount of mass being "lost" and converted into a huge amount of energy according to Albert Einstein's most famous equation--

Theoretical Physicist Albert Einstein (1879 – 1955) and his famous equation showing that a tiny bit of mass can be converted into a huge amount of energy. "E" is for "Energy," "m" is the amount of mass converted to energy, and "c" is the speed of light-- 186,000 miles per second. According to this equation, a mere ounce of mass completely converted to energy would yield an explosion

equivalent to that of 6 million tons of TNT.

This conversion of nuclear mass into pure energy generally happens two different ways-- splitting the nucleus of a large atom (like Uranium or Plutonium) into the nuclei of smaller atoms is called nuclear fission, while mashing together the nuclei of small atoms (like hydrogen) into a larger nucleus is called nuclear fusion. (Sunshine comes from an ongoing fusion reaction 93 million miles away.) In both types of nuclear reactions, a small amount of "lost" mass is converted into a tremendous amount of energy. On the eve of World War II, the possibility of harnessing such nuclear reactions for electricity-producing power plants as well as a whole new class of military weapons was apparent to theoretical physicists of the era, and Einstein himself warned U.S. President Franklin D. Roosevelt of the urgency of developing a nuclear bomb before the Germans did.

Thus was born the Manhattan Project.

The gathered physicists at Los Alamos understood that a fusion bomb would be far more powerful than a fission bomb; a fusion bomb, however, would require a fission bomb to initiate the reaction and set it off, and so, since the project was considered so urgent, they kept their focus on developing a fission bomb. (At this point it might be worth watching the epic movie Oppenheimer, if you haven't done so already.)

A fission bomb requires material that splits into smaller atoms and while doing so emits neutrons that strike other nuclei and cause them to emit neutrons that cause more fission, and so on... i.e., a chain reaction. Uranium makes an excellent such fuel for fission bombs, so long as a sufficient amount of the right type of Uranium is available...

Which brings us to isotopes.

The tally of a Uranium atom's protons and electrons-- 92 each-- remains fixed; however, the number of Uranium's neutrons can vary, giving us what are called isotopes of the same atom. Most Uranium as found in nature (99.3%) is the Uranium isotope U-238, which has 146 neutrons, while the remaining .7% is the isotope U-235, which has 143 neutrons. U-238 is quite stable; U-235 is also stable yet highly fissile, i.e., it can be prompted to undergo a nuclear fission chain reaction by either bombarding it with neutrons or just cramming enough of it (a "critical mass") in a confined space. Separating U-235 from raw Uranium that is 99.3% U-238 requires a machine known as a centrifuge.

Your salad spinner is a centrifuge that separates water from lettuce.

With its three fewer neutrons, U-235 is slightly lighter than U-238. To separate one from the other, scientists combine Uranium atoms with Fluorine atoms to form Uranium Hexafluoride (UF₆) molecules, which turn directly from a solid to a gas at 134ºF. Then they spin the UF₆ in a salad-spinner-like centrifuge, and the UF₆ molecules containing U-238 atoms are forced outward, leaving a greater concentration of U-235 Hexafluoride in the middle. They remove some of the UF₆ from the middle of the centrifuge, and then repeat... over and over again, thousands of times. This process is known as Uranium enrichment. Increasing the concentration of U-235 from .7% to 3-5% is enough to run a nuclear power plant, but nuclear bombs require enrichment all the way to 90%.

Due to the onerous logistics of enriching Uranium, the Manhattan Project physicists at Los Alamos had only enough U-235 for ONE bomb. However, they considered it a scientific certainty that this single Uranium bomb-- the one that would be dropped on Hiroshima-- would work as designed, and so no testing was necessary. The bulk of the work at Los Alamos was instead directed toward the development and testing of a very different type of fission bomb, one that used Plutonium-239 instead of U-235 as well as a far more complicated detonation mechanism. (See A Tale of Two Bomb Designs.) The first fusion bomb became operative in 1952, seven years after the successful deployment of the first fission bomb. (See history HERE.) The new bomb-- considerably more complex and potentially thousands of times more powerful than its predecessor-- became known as the "Hydrogen" bomb for the components of its fusion reaction, or alternatively as the "thermonuclear" bomb for the tremendous fireball it generates.

The "Castle Bravo" test blast, 1954. See details HERE.

Dear Reader, if you've made it this far, you now know more about nuclear physics than 99% of the general population. So... what's the point of all this history and background?

Because of the complexity and necessary technology required to produce a fusion bomb or even a Plutonium-239 fission bomb, it seems reasonable to conclude that a rogue nation or a sufficiently funded and motivated terrorist organization bent on acquiring nuclear weaponry would focus its efforts on developing a primitive yet reliable U-235 fission bomb...

Which brings us back to the present Iranian regime and their (now former) Uranium enrichment program.

Despite Iran's repeated denials, it was hardly a state secret that they were pouring considerable effort and resources into enriching U-235 to a concentration sufficient to produce a nuclear bomb... what else would all those underground centrifuge facilities be for? Iran has also been hard at work developing missiles capable of launching such weapons toward targets in other countries, including the United States. But did that give the United States the right to preemptively destroy Iran's nuclear technology? Because of a potential threat? That is another question for another forum. At least now you have some idea what type of bomb Iran was developing, and how... details that the nightly network news doesn't seem interested in covering.

If you've found this explanation informative and useful, please share it with friends.

NOTES:

The "Bunker Buster" bombs dropped by the United States were NOT nuclear bombs, but rather conventional bombs with the ability to penetrate deep underground, even through thick layers of solid rock.

Albert Einstein enjoyed a very busy year in 1905... dubbed his "Annus Mirabilis," or "Year of Wonders." He published FOUR seminal articles on theoretical physics that year. (See HERE.) Contrary to popular misconception, the equation for which he is best known-- E=mc² -- is NOT Einstein's "theory of relativity," but they are related.

And finally, with your newfound understanding of nuclear physics you might enjoy reading a PDF of a translated Soviet summary of nuclear weaponry. Click HERE.