1900: A physics genius wandering around Europe

Chapter 698 Unveiling the Manhattan Project! Uranium Separation Plant! Nuclear Reactor! Design and Manufacturing Laboratory!

The Manhattan Project was able to succeed so quickly not because it did not encounter any research and development difficulties.

On the contrary, Oppenheimer and others encountered many technical difficulties.

However, these problems became less difficult with the US government pouring money into the project, increasing the funding from $4 million to $20 billion.

"Problems that can be solved with money aren't problems at all!"

"Try any ideas you have right away!"

Scientists, if given unlimited resources, can indeed unleash terrifying power.

A single image is enough to show the complexity and scale of the Manhattan Project.

In September 1942, after Groves took office, he first purchased his first piece of land in Oak Ridge, Tennessee.

One of the core facilities of the Manhattan Project, the uranium-235 separation plant, was built here.

For weapons-grade uranium, its purity must reach over 90% to allow for a chain reaction.

Of the naturally occurring uranium element, uranium-235 has an abundance of only 0.7%.

From 0.7% to 90%, what an incredible purification rate!

At that time, scientists proposed a total of three separation and purification methods.

The first method is the "gas diffusion method" proposed by Yuri, a student of Lewis:
First, elemental uranium (containing three isotopes) is converted into uranium fluoride gas, and then this gas is passed through a plate with many fine holes.

According to thermodynamics, when uranium fluoride gas passes through a narrow pore, the lighter uranium-235 molecules diffuse faster than the heavier uranium-238 molecules.

Therefore, the uranium-235 content on one side of the perforated plate will increase.

By passing these gas molecules through 5000 plates in succession using this method, the purity of uranium-235 can be greatly improved.

This method is highly efficient and can separate a large amount of uranium at once.

However, the drawbacks are also obvious. It is difficult to achieve a purity of 90% for uranium-235 because the diffusion of the gas is chaotic and will always be mixed with uranium-234/238.

The second method is the "electromagnetic separation method" proposed by Lawrence:
The principle behind this method is very simple: place elemental uranium in a cyclotron.

Because of the slight differences in mass between uranium-235 and uranium-234/238, the rotation radii of the three isotopes are different.

Uranium-235 atoms can be isolated individually by controlling the electromagnetic field and then guided out of the accelerator.

The advantage of this method is that the purity of uranium-235 is very high, even reaching over 95%.

However, the drawback is also obvious: the efficiency is simply too low.

Because the cyclotron cannot add too much material at once, otherwise it is easy to cause problems.

At this point, you, being so clever, must have thought of:

"Then let's combine the two methods."

Indeed, after scientists discovered this, they first used gas separation to perform "coarse enrichment," and then used electromagnetic separation to perform "fine enrichment" of the coarsely enriched uranium.

In this way, not only was the efficiency of uranium separation improved, but the purity of uranium-235 was also greatly improved, meeting the requirements of an atomic bomb.

The third method is the thermal diffusion method proposed by Ebersen. (The principle is similar to the gas diffusion method, except that it is thermally driven.)
At the time, unsure which method was best, the US government made a decision immediately:
"Perform all three methods simultaneously!"

Each of these three methods requires building a separate factory, equipping it with massive machinery, and is extremely costly. (See figure)

This demonstrates the United States' financial strength and determination.

As a result, the Oak Ridge uranium separation plant became a super-large factory complex with a regular workforce of over 8 people.

It is also the part of the Manhattan Project that received the most investment.

Soon, through continuous trial and error, the thermal diffusion method was eventually phased out.

The uranium separation plant decided to adopt a combination of gas diffusion and electromagnetic separation methods.

Both of these methods are extremely energy-intensive, together accounting for one-sixth of the total electricity consumption in the United States that year.

Over the course of three years of the Manhattan Project, the Oak Ridge uranium separation plant consumed several thousand tons of uranium ore, but ultimately only separated more than 70 kilograms of uranium-235.

With the raw material issue resolved, another problem became urgent.

How can controlled nuclear fission be achieved using uranium?

Although the atomic bomb itself is an uncontrollable nuclear fission, studying it requires controlled experiments.

Uranium-235 is so precious that not a single drop can be wasted.

At this critical moment, Fermi was appointed to the post.

He was in charge of building the nuclear reactor at the University of Chicago.

Incidentally, Groves had great respect for these scientists and even allowed them to work at his school.

Therefore, you will find that the administrative headquarters led by Groves is in Manhattan on the East Coast①, while the scientific headquarters led by Oppenheimer is in Berkeley on the West Coast②.

The nuclear reactor led by Fermi was located in Chicago in the Midwest.

Communication between the three locations would be very inconvenient, but Groves still agreed.

And all of this stemmed from a single sentence by Oppenheimer:

“We prefer the atmosphere at school.”

Fermi led a team of dozens of top scientists, including Szilard, at the University of Chicago to begin the construction of a controlled nuclear reactor.

Compton was in charge of overseeing the project, and publicly claimed that it was just a regular research project.

When Compton learned that Fermi wanted to build a nuclear reactor directly inside the University of Chicago, he was terrified.

“Brother Fei, if we can’t control this, the whole of Chicago will be wiped out.”

However, Fermi simply stated domineeringly:
"I won't let it happen."

The construction of a nuclear reactor is not without its challenges.

To achieve a controllable nuclear chain reaction, the speed of neutrons must be controlled.

Do you remember Fermi's earlier discovery that hydrogen in water could slow down neutrons?
Fermi believed that using heavy water might be even more effective.

The bigwigs made the request, and the US government immediately invested $2600 million to build a heavy water production plant in Canada.

However, after Fermi tested it with heavy water, he found that the effect was not as good as he had imagined.

So he suggested again: try using graphite.

The US government had no complaints about this, and the previous heavy water plant was considered a waste of money.

Graphite is no longer so precious; large private companies supply it readily.

Soon, the research finally achieved a breakthrough! (We can't describe too many details about nuclear reactors.)

1942年12月2日下午3点25分。

When the neutron counter emitted a slight vibration, the first controlled nuclear reactor in human history was born!

This nuclear reactor consisted of 40,000 graphite blocks encasing 19,000 pieces of uranium material, and it lacked any protective system. Fermi and his team were risking their lives.

Its initial output power was only 0.5 watts, not even enough to light a light bulb.

However, it signifies that humanity has officially entered the atomic age and stepped into a new historical stage!

This reactor was later known as the "Chicago Pile-1", or simply "CP-1".

Fermi's team's success inspired all the scientists on the Manhattan Project.

At this point, Groves approached Oppenheimer and sincerely said:

"Now that we have uranium materials and the principles of nuclear reactors are understood, we can begin designing and manufacturing atomic bombs." "But this work can't be done within the university, can it?"

Oppenheimer thought about it and realized that a dedicated laboratory was indeed needed for the research.

In March 1943, Los Alamos Laboratory was officially completed in a desert in New Mexico, USA.

Groves personally oversaw the operation, leading 3000 fully armed soldiers to protect the laboratory.

The Los Alamos Laboratory has extremely high confidentiality requirements.

The entire laboratory is located in a valley, isolated from the outside world, and can only be accessed by a small path.

Each factory and residential area has a code, and all mail coming and going is subject to strict censorship.

Every researcher in the lab had their ancestry traced back three generations.

Even ordinary workers who work here must undergo rigorous screening.

Each person can only understand a small part of what is within their own scope of responsibility, and doesn't know what they are actually doing or what the meaning of their work is.

One worker recalled:

"My job is to open the valve."

"When the number moves from 0 to 100, the valve is opened once; when the number returns from 100 to 0, the valve is opened again."

"The whole day has passed."

"The same thing happened the next day."

Moreover, no one is allowed to ask questions or raise objections; otherwise, they will be taken away for isolation and investigation.

Groves brought the same stringent requirements to the Oak Ridge uranium separation plant.

For example, in a gas diffusion separation device, there is a key component called a filter.

At that time, a large number of female workers were specifically responsible for processing the raw materials for filters.

Strangely, each of these female workers had to report their menstrual period immediately and was absolutely not allowed to hide it.

During their menstrual period, female union members are assigned to work in a different group and will return after their period ends.

Although the female workers were very curious, none of them dared to ask why, and could only obediently do as they were told.

It turns out that women sweat more during their menstrual period, so the sweat on their hands can easily contaminate the filter material, resulting in insufficient purity.

This is the secrecy and strictness of the Manhattan Project.

In real history, only 12 people knew the full picture of the Manhattan Project.

Even the newly elected President Truman didn't know what the plan was actually about.

The president of the University of California saw Oppenheimer there and assumed he was researching a "death ray" weapon.

In short, uranium separation plants, Chicago Reactor 1, and other such preliminary work are all necessary steps.

The ultimate goal was to design and manufacture the atomic bomb at the Los Alamos laboratory.

Oppenheimer became the laboratory director.

CP-1 was also moved from Chicago to the laboratory and was improved and optimized to become CP-2 to meet the experimental requirements.

At first, Oppenheimer was full of confidence and said domineeringly:

"I only need 6 physicists and more than 100 technical engineers to build an atomic bomb."

However, the difficulty of developing the atomic bomb still exceeded his imagination.

Soon, the research team exceeded 1000 people, and almost all physicists in the United States participated at that time.

The most important and core part of the laboratory is the theoretical department, where big names such as Feynman, Fermi, Bohr, Taylor, and von Neumann were all.

This department is responsible for researching and calculating the principles of atomic bomb explosions, and its director is 37-year-old Beth.

Beth was Sommerfeld's doctoral student who was forced to flee Germany to the United States because of his Jewish heritage.

He made groundbreaking contributions to quantum mechanics, nuclear physics, particle physics, and astrophysics, and was awarded the Nobel Prize in Physics in 1967. (He was an incredibly brilliant person, but describing his brilliance is too technical.)
The first task of the theoretical department was to calculate the critical mass of uranium-235.

The critical mass refers to the minimum mass of fissionable material required to sustain a chain reaction.

Because if the mass of uranium is very small, it means that its volume is also very small, so neutrons can easily penetrate the material and escape to the outside, causing fission to stop.

Therefore, the mass of uranium material inside an atomic bomb must exceed the critical mass.

In addition, the shape, purity, and other properties of uranium materials can affect the critical mass value.

To make an atomic bomb, the uranium material would definitely undergo various structural designs, which would cause slight changes in the critical mass.

Therefore, physicists in the theoretical department calculated the simplest case: perfectly spherical uranium material.

Heisenberg miscalculated on his own at the time.

However, the theoretical department has more than a dozen or even dozens of top experts, so the possibility of a calculation error is zero.

The final result was 50 kilograms.

Even if the critical mass changes due to different final structural designs, it will only be an increase or decrease of a few kilograms.

Upon seeing this result, Oppenheimer and the others were immediately disheartened.

According to data from the Oak Ridge uranium separation plant, they can only purify more than 70 kilograms of uranium-235 within three years.

In other words, there is only enough uranium material to make one atomic bomb!

How can we test the explosion then?
How can we be sure that the theory and design are correct without trying them?
If we accidentally launch a dud, the Sakura Clan will probably laugh us to death.

Just when everyone was at a loss and in a state of panic, Seaborg (not Szilardha) suddenly remembered plutonium, element number 94, which he had created.

"Plutonium-239 can also undergo nuclear fission."

Why not try it?

Everyone was overjoyed.

Calculations show that the critical mass of plutonium-239 is only 5 kilograms.

Moreover, the process for manufacturing plutonium-239 is very mature, and the raw material used is uranium-238, which was previously not needed by uranium separation plants.

Uranium-238 can be irradiated with neutrons to obtain plutonium-239.

Soon, following Fermi's experience, Seaborg led his team to build a plutonium reactor and verified the mechanism of the plutonium chain reaction.

Then, the U.S. government spent $3.9 million to build a plutonium-239 manufacturing plant in Hanford, Washington.

Incidentally, the Oak Ridge uranium separation plant later also began purifying plutonium-239.

According to progress feedback from the Hanford City plant, there is enough plutonium-239 to make two atomic bombs.

Oppenheimer and the others were finally relieved.

Next, the Theoretical Department needs to tackle the second and most crucial task:
How exactly was the structure of the atomic bomb designed?

If we disregard all other factors, imagine holding a 30-kilogram piece of uranium-235 in both your left and right hands.

The moment the hands come together, a nuclear chain reaction begins. (This is because free neutrons also exist in the air, which can potentially trigger a nuclear reaction.)
This method is probably the favorite of terrorists.

However, the factors to consider when creating a controllable weapon like the atomic bomb are much more complex.

As the experts delved deeper into their research and calculations, two completely different design approaches emerged.

After thinking for a moment, Oppenheimer waved his hand:
"The theoretical department has been divided into two groups to study these two design principles simultaneously!"

(End of this chapter)