Nuclear Fission: Unleashing The Power Of The Atom

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When thinking about discoveries that have changed the world, most of the time it’s for the better. However, there are some discoveries where you wonder if the world would have been better off without them. One of these is the ability to harness the power of nuclear fission. This gave us the ability to unleash almost unlimited fury and destruction on a global scale with the atomic bomb. Today, were going to learn the interesting story behind what led scientists to figure out how to split atoms along with a bit about how it works.

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The Science And Story Of Nuclear Fission And Atomic Weapons

When thinking about discoveries that have changed the world, most of the time it’s for the better. Discovering penicillin allowed us to fight bacteria and save lives. The pacemaker helped to keep our hearts beating. Pushing forward plant breeding and genetics helps us feed the world, among countless others.

However, there are some discoveries where you wonder if the world would have been better off without them. One of these is the ability to harness the power of nuclear fission. This gave us the ability to unleash almost unlimited fury and destruction on a global scale with the atomic bomb.


We saw what happened in Japan during World War II; pure carnage where the two bombs were released. Then, following World War II, one of the only things keeping superpowers from obliterating each other is the fear of mutually assured destruction, meaning if we wipe them out, they wipe us out.

We now have the power to destroy almost all life off of the face of the Earth many times over. With nuclear energy, we also have a relatively sustainable and clean source of energy as long as we can keep it safe and dispose of the toxic waste properly. With this technology being so new, there are still many wrinkles that need to be smoothed out.

Today, were going to learn the interesting story behind what led scientists to figure out how to split atoms along with a bit about how it works.

The Discovery Of Nuclear Fission

The early to mid-1900s were a booming time for the advancement of chemistry and physics. Discoveries were popping up seemingly everywhere and knowledge was being uncovered at a rapid rate. In the early 1930s, scientists began to get a much deeper understanding of the structure of the atom by bombarding it with sub-atomic particles.

At the same time, they were also trying to see if they could split atoms by blasting them with smaller particles. Unfortunately for them, none of their attempts were successful.

Finding The Neutron

Before the 1930s, it was well known that the mass of an atom was roughly twice it’s atomic number. Just as a quick refresher, the atomic number is the number of protons held inside the nucleus. For example, helium has an atomic number of 2, but an atomic mass of 4. Since electrons practically have no weight, there was something missing from the picture.  

It was commonly thought that atoms are made up of only protons and electrons. This doubling of the mass was somewhat of a mystery. Scientists knew that essentially all of the mass of an atom was in the nucleus, but electrons couldn’t possibly make up that extra weight because that would just simply be too much energy to have the positively and negatively charged particles that close to each other.

Whenever there is an obvious mystery like this, you can almost always guarantee that a scientist somewhere is working to figure out what’s going on. In this situation, an English scientist named James Chadwick was on the case.

German scientists had already been finding some interesting results by bombarding beryllium with alpha particles. Alpha particles are pretty much helium without its electrons. What they found was that when beryllium was hit by the alpha particle, a neutral radiation would be emitted.

This means that they could detect some particle being knocked off, but it was neutral. They thought this was very interesting, but didn’t really know what it was.

Chadwick kept pursuing this and came to the conclusion that the radiation being emitted was actually a neutral particle being broken off from the nucleus. In 1932, Chadwick put out a paper titled “The Existence of the Neutron” in which neutrons were found to be their own particle bound up in the nucleus.

While this was an awesome discovery, you might be wondering why we are talking about it when the topic is supposed to be nuclear fission. Well, the discovery of the neutron was essential to figuring out how nuclear fission works. The discovery was so important that Chadwick actually ended up receiving the Nobel Prize.

This is a good video explaining the entire story behind the discovery of the neutron.

Using The Neutron To Split Atoms

The discovery of the neutron quickly changed the way scientists viewed and probed the atom. Previously, a majority of the work being done to determine the structure and properties of atoms was done by shooting positively charged particles at the nucleus of atoms using a particle accelerator like we talked about earlier.

However, positively charged particles really don’t like running into a positively charged nucleus. Einstein compared it to going bird hunting where there is a single bird and it’s pitch black outside. The success rate was only about one in a million. I don’t know about you, but I definitely wouldn’t bet on those odds.

However, now that the neutron had been discovered, it could be shot at the nucleus of atoms and avoid the harsh resistance that alpha particles experienced. Using neutron bombardment, scientists got to work.

The First Nuclear Fission

In 1934, an Italian physicist named Enrico Fermi shot uranium with neutrons and thought he made the first known element that was heavier than uranium. At the time, it was thought that bombarding elements with neutrons could only make small changes. So, maybe it would knock a proton off or possibly a few neutrons would end up sticking to the nucleus.



He shot neutrons at 63 different elements, and most of the time, it would make a slightly heavier atom. However, sometimes the products made it seem like the uranium was actually getting broken into lighter elements. At the time, this was thought to be impossible.

Other scientists looked at this work and realized that rather than making a heavier element, it was also a possibility that smaller elements could be made if the uranium was broken apart. This was the first time nuclear fission had ever been accomplished, or in other words, the first time an atom had been split, but from my research, it seems like not enough analytical work was done to confirm that smaller elements had been made.

They knew something important was going on, but not exactly what. Most scientists reading the results thought that mass was being added to the uranium, but like I said earlier, they just assumed that it was impossible to break uranium into smaller products by shooting neutrons into it. This really shows us how important it is to question our assumptions.

Fermi’s initial research was a massive breakthrough for science and the world, but at the same time, the science and knowledge of what happened was a bit vague. Much more research needed to be done in order to fully understand and use nuclear fission.

Picking Apart The Details Of Nuclear Fission

Following in Fermi’s footsteps, in Germany two physicists named Otto Hahn and Lise Meitner and then a chemist named Fritz Strassman got to work classifying what was actually happening here. They started flinging neutrons at many elements, including uranium, carefully characterizing everything that was observed.

They were making a lot of progress, but because of Meitner’s Jewish heritage, she was forced to flee Germany in 1938. Her research was her entire life, but because of the political climate in Germany once Hitler took power, she had to leave to Sweden with just two small suitcases.

There are so many examples throughout history and even in previous episode that I’ve done showing how politics can slow the progress of science that could help us all. Imagine how much farther we could’ve made it if the whole world was peaceful and cooperated. Maybe that’s just a fantasy I have, but it would be awesome if we reach it someday.

Despite this setback, Meitner still acted as an advisor while Hahn and Strassman continued their work. Hahn kept finding that there was some barium in the decay products, which is a much lighter element than uranium. They were stumped.

Lise Meitner and Otto Hahn

Lise Meitner and Otto Hahn

What If The Nucleus Wasn’t Solid?

Over Christmas, Meitner met with her nephew who was a physicist. They knew that Hahn was a good chemist and didn’t keep finding lighter elements by mistake, so an intense brainstorming session led to some interesting thoughts.

Meitner thought about treating the nucleus of an atom like a drop of water rather than the solid mass model that other scientists had proposed. Her nephew was great at visualizing scientific concepts and made some drawings showing how if the nucleus would react by getting hit by a neutron.

His drawings showed the nucleus becoming elongated after the initial force was absorbed, then pinching in the middle and separating into two. Once split, the positive charges on the two separate nuclei would cause a huge force driving them apart.

Then, things get a bit weird. They knew already that the masses of the products were slightly lower than the starting uranium from calculations and experiments. They found that per atom of uranium that was split, the mass lost was about 1/5th of a proton.

Using Einstein’s famous equation relating mass to energy, E=mc^2, they calculated the amount of energy that would be released if 1/5th of a proton disappeared to be 200 million electron volts. There’s really now way of putting that amount of energy into perspective, so lets just say that is a huge amount of energy for a single atom to release.

Then, further tests measured the amount of energy actually released in an experimental setting and this number was confirmed. The hypothesis Meitner and her nephew came up with over Christmas proved to be correct. It was also the first time that Einstein’s theory had been proven experimentally.

Let’s Sum It Up So Far

So, this was a lot of information thrown at you all at once, so let’s summarize a bit so we can get the whole picture. Fermi discovered that neutrons fired at the nucleus of many different elements induced changes in the atoms. Most of the time, it just made the atom a bit heavier, but there were some signs that maybe it could cause some actual breakdown in the element.

Then, three other scientists started to test this in much more depth and classified everything that was happening. They found that sometimes, the product of uranium being hit would produce elements that were much smaller than uranium, which was very confusing.

After some theoretical models were thought up by Meitner and her nephew, they said that maybe the nucleus gets split into two parts when hit, making the smaller elements that were found. They also calculated that mass would be lost in the process and plugged this into Einstein’s equation relating energy and mass.

It turns out that the amount of energy they calculated was proven experimentally. The nucleus of uranium gets split into two smaller elements and causes a massive release of energy. They figured it out and her nephew, Otto Frisch, coined the term fission which literally means splitting into two or more parts.

 They came out with a paper in the journal called Nature and it started to gain traction. Further research found that when this breakdown happened, neutrons from uranium would also get launched free in addition to the breakdown into smaller parts.

This video does a good job summarizing what Meitner and Frisch found with a bit of Meitner’s story.

If these neutrons that were broken free could hit the nuclei of other uranium atoms, it could cause a massive chain reaction and release exponentially more energy every time this happened.

If you had a pile of uranium, just one neutron hitting one uranium nucleus could cause the rest to react and cause a massive source of energy leading to an explosion. This is where things get a bit dicey. I think you can probably see where this is going.

Putting Nuclear Fission To Use

The news of this discovery made it to the US when scientists from Europe discussed the work at a theoretical physics conference in Washington D.C. At that time, the US had a really interesting community of physicists who were great at working as a team and also had a focus on actually experimenting rather than just coming up with theories and plugging in math.

I’m not saying that theoretical physics isn’t important by any means, but in this case, having an experimental focus really helped push science in the United States. One scientist named Ernest Lawrence who had a huge drive and passion to push this new technology forward made the Berkeley Radiation Laboratory the center for nuclear physics in the United States.

Figuring Out How To Cause A Chain Reaction

Interestingly, because of this America led the way for developing nuclear physics equipment and developing the field as a whole. Physicists really started to explore the possibility of a chain reaction like we talked about earlier because that’s where the power would come from.

Sure, a single atom can release massive amounts of energy on its own, but not enough to have a practical use to people. If you could figure out a way to cause a chain reaction throughout a large mass of uranium, you could create an amount of power caused by humanity that blows anything before it out of the water. No pun intended.



We also have to step back in time and take a look at the political climate. World War II had just broken out and most of the initial research into nuclear fission was taking place in Germany. If the Germans were able to harness the power of nuclear fission and weaponize it before the Allies, it would be devastating.

Interestingly, nuclear physics was also popping up all over Russia, and with good progress. However, if you know anything about Russian history, you know that it wasn’t a safe place to live as the government would openly kill or imprison huge numbers of people.

Many of these people were scientists, so nuclear physics progress was slowed. In fact, it was reported that half of the top scientists working on nuclear physics in Russia were put into prison at one point. This heavily stunted the Russians.

War Pressure Drives Research

So, due to this pressure, the Allied powers worked hard to develop a chain reaction of nuclear fission. It was also known that there were two main isotopes of uranium, so work started being done to determine which form would produce the most sustainable chain reaction to put nuclear fission to use.

Before we go any further, let’s talk about what an isotope is. Don’t worry, it’s not very complicated. So, we already know that every atom has a certain number of protons. Uranium has 92, and that’s what makes it uranium. The elements and their properties are determined by the number of protons in the nucleus.

However, we also now know that inside the nucleus there are neutrons. When two atoms have the same number of protons but a different number of neutrons, they are isotopes. They are the same element, but because they have a different number of neutrons, they have a different atomic mass.

For uranium, the two most common isotopes have a mass of 235 and 238. Since they both have the same number of protons, they are different because uranium-238 has 3 more neutrons than uranium 235. Another important fact is that uranium-238 is way more common in nature than uranium-235.

A study done at the University of Minnesota in 1940 concluded that for every 140 naturally occurring uranium atoms, 1 would be uranium-235 and almost all the rest would be uranium-238. This was very important for the chain reaction scientists were working towards.

Scientists Need To Isolate Uranium-235

Now, the reason this is important is because in order to split, uranium-238 requires the neutron hitting it to be much faster than uranium-235. The neutrons emitted once uranium is split just don’t have enough energy to cause another uranium-238 to split. However, they are fast enough to cause uranium-235 to split.

This all means that scientists discovered that if you wanted to have a spontaneous chain reaction of nuclear fission to occur, you would need a very pure of uranium-235. This was no easy task since it comprised just .7% of naturally occurring uranium, which was already a rare metal in the first place!

Science came all this way and made so much progress just to realize that it was going to get much harder to make this work before reaching their goal. At the same time, they knew what had to be done and got to work. Don’t you hate it when that happens?

It turns out that there is a critical mass that needs to be obtained to get a spontaneous reaction to happen. This means that once you hit a specific percent of uranium-235, the reaction go forward. If you were just trying to use nuclear fission for energy, the percent is lower because it doesn’t need to happen as fast. However, for a nuclear weapon, the reaction needs to happen much faster.

Another issue with the slow uranium-238 is that since it would react slower, the initial explosion would blow apart your chunk of uranium before it could even react. Anyways, scientists still needed to find a way to get enough uranium-235, which was called enriched uranium.

This is sort of what they were going for.

Making The First Atomic Weapon

Two physicists named Peierls and Frisch came out with a three-page document where they predicted that 5kg or about 11 pounds of uranium-235 would make a bomb the same size as several tons of dynamite. This was then changed to 8kg or about 17 lbs.

They also showed in their proposal how to detonate the bomb, how to produce the bomb, and then proposed what the radiation damage would be like. This proposal stimulated much more interest in Britain than the United States at the time.

American research continued, but British research began to pick up as well. The US was more focused on the use of nuclear power for energy and naval ships. There was a lot of secrecy even amongst the Allies, but occasionally some scientists who let their ego take control would publish a paper here or there to get their name recognition.

It was estimated that to produce 1kg of U-235 per day, it would cost about upwards of $10 million dollars per day which was a copious amount of money back then. It would also require a large, very skilled workforce at the factory.

By the middle of 1941, the British and Americans, through Winston Churchill and the US military Chiefs of Staff, agreed to work together to put nuclear power into a weapon. This was majorly boosted when the Japanese attacked Pearl Harbor in December of 1941.

The US Takes Over Atomic Weapon Production

In 1942, the US Army took over the development, engineering and most of the research towards getting the materials, building manufacturing sites and then making U-235. It was at this point that scientific communication was cut off to Britain and the rest of the world.

This secret program to get a nuclear weapon in the US was codenamed ‘The Manhattan Project’. Back in 1941, Fermi and an associate at the University of Chicago came up with a design for a uranium chain reactor. The uranium was placed in a 36-foot stack of graphite that was shaped into a cube. They set it up under an athletic stadium at the university.

Out of all the places to set up a nuclear reactor, I probably wouldn’t choose to put it underneath a stadium that would fill with people, but it worked. They surrounded the reactor with cadmium rods because cadmium actually absorbs neutrons.

Using the rods, they could control the amount of neutrons hitting the uranium and because of this, they could control the speed of the reaction. At least they had some sort of mechanism to keep the reaction under control.

They demonstrated their work on December 2, 1942 and catapulted the world into the nuclear age. Their nuclear reaction became self-sustaining and it was the first real demonstration of a controlled nuclear reactor in use. The next step was putting this into the form of a bomb.



Getting a Pure Sample Of U-235

Alongside this work was attempts to separate U-235 from U-238. There were many techniques being used because the governments involved didn’t want to rely on just one. Quite frankly, scientists didn’t have time to find the best way to get more U-235, so they were like “hey, let’s just do everything and one has to work, right?”

The first was to get uranium into a gas and diffuse it across a barrier. The concept was fairly simple, being that the lighter U-235 should pass through a porous barrier more easily than the heavier U-238. Unfortunately, it was very challenging to make a good barrier for the U-235 to pass through and also it was hard dealing with large amounts of the gas as it was extremely toxic.

Other methods were used such as putting it in a centrifuge, spinning it really fast and getting it to separate. Since U-235 is lighter, it would rest on top of the heavier U-238. This method took so much energy and the centrifuges broke down so often that the US stopped using it, but other countries till use it to this day.

Electromagnetic separation was also thought about. U-235 should be more deflected by a magnet since it’s lighter, which would lead to separation. However, the difference was so small that it was estimated to take 27,000 years to get just one gram of pure U-235. Unfortunately, that just wasn’t going to work.

Finally, a technique called liquid thermal diffusion was also tried, but not for long. They would pass liquid uranium hexafluoride through a tube. One side of the tube had a heater, and the other side was cooled. They found that U-235 would concentrate near the hot wall, but again, there just wasn’t enough being produced.

Getting To Work With Gas Diffusion

In the end, the gas diffusion method, despite being dangerous had the highest yield, so scientists went to work. When almost all of the major powers in the world were at war, it was a time where scientists started taking risks.

More on how the gas-diffusion method worked.

Getting enough U-235 proved to be the hardest part in putting nuclear fission to use. It seems like we are only talking about the use for weapons, so I want to say that in some places nuclear energy was being researched as well. However, the focus would be on weaponizing nuclear power until the end of the war.

A bi-product of the nuclear reactor tests was a new element that had never been seen before called plutonium. Somehow, during the reaction a portion of the uranium atoms would actually gain a proton and turn into a new element called plutonium. This new element would also split and release a large amount of energy, so it started to be used as well.

The US & Britain Cooperate To Make U-235 and Plutonium

After many months of negotiation, the US and Britain started to cooperate again in 1943 to get enough U-235 and plutonium made. The US government estimated that $1 billion would be the total cost for the nuclear program which was almost 100% focused on making a bomb like I said earlier.

Shortly after, a team under Robert Oppenheimer in Los Alamos, New Mexico designed and constructed the first uranium and plutonium bombs. Through a massive effort by the American and British scientists, politicians, and manufacturing industries, enough uranium and plutonium was produced by 1945 to make a functioning weapon.

Interestingly, most of the uranium came from the Congo. I’m assuming this was done unethically as the Allies were willing to do whatever it took to get the material, but that’s just an assumption on my part.

The First Atomic Weapons Are Tested And Used

On July 16, 1945 the first atomic weapon was successfully tested. Then, just a month later, a U-235 bomb was dropped on Hiroshima, Japan and then 3 days later, a plutonium bomb was dropped on Nagasaki.

To this day, the decision to use nuclear weapons is a topic of hot debate. Was it ethical to kill over 100,000 civilians to bring an end to one of the most devastating wars the world has ever seen? I’ll leave that for you to decide.

 Nuclear Energy Production

I think we’ve covered this topic pretty well and should have a good understanding of how nuclear fission works and what it meant to the world. Before we go, I want to quickly cover what this meant for energy production though.

It was found that a controlled nuclear reaction would produce tremendous amounts of heat. The idea of turning this heat into energy was first tested at the Argonne National Laboratory in Idaho in December, 1951.

The concept is very similar to how coal burning plants work. The heat from the nuclear reaction heats up water and turns to steam which is then converted to energy. The upside is that instead of shoveling massive amounts of coal into a furnace releasing tons of smoke and pollutants into the air, you could use a relatively small amount of uranium to generate the same amount of power.

The technology kept advancing and nuclear power plants started to pop up all over the place. The building of new plants started to slow in the 1970s and 1980s. There were increasing concerns about the safety of nuclear power plants and what could happen if one melted down, and we have seen this play out in Russia and Japan.

For a long time, the US led the world in nuclear power plants, but today, China is by far putting the most resources into nuclear power because of the vast amount of energy that can be produced without polluting the air. They’re not too worried about finding a place to put all of the toxic waste that will remain toxic for thousands of years.

Now, Nuclear Fusion Is Used

One last thing; as the years passed, nuclear fusion is a new technology that started to take over fission. Fusion is sort of the opposite of fission, being that a massive amount of energy is released when two atoms join together rather than split apart.

Fusion utilizes much smaller atoms like hydrogen which is much more plentiful than uranium or plutonium and is also much less toxic. It also creates less radioactive waste. I don’t want to get too far into fusion, so look out for a future podcast episode on that.

 It’s Up To Us To Use This Technology Responsibly!

The ability to harness the power of the atom has changed the world. It’s a technology that has been deeply intertwined with global politics and is very two-sided. On the one hand, the amount and power of weapons made could end almost all life on the planet. For sure human life at least.

On the other, we now have an amazing and relatively clean source of energy, although continuing efforts are being made to keep the plants safe. There is a lot off debate over whether or not this technology has been good for people or one of the worst things to ever happen to humanity.

I think it’s a net positive. If we could all get over our petty disagreements and put nuclear weapons along with the hostility caused by them aside, I think nuclear power could be one of the greatest achievements humanity has ever made. Like with anything, it’s just how we use it.