1900: A physics genius wandering around Europe

Chapter 699 Gun-style! Implosion-style! Miniaturized nuclear bomb! [Skinny guy] [Fat guy] [Little boy]!
The basic principle of the atomic bomb is very simple.

As long as the mass of uranium-235 exceeds the critical mass, the "ignition" neutron source can release neutrons and initiate a chain reaction.

Based on this principle, the bigwigs in the theoretical department of Los Alamos Laboratory quickly came up with a simple structure.

This structure is called the "gun-style" and is a simple and crude physical assembly.

Gun-type atomic bombs are generally long and slender cylindrical, with an overall structure very similar to artillery shells.

The core principle of the pistol style is:

"The shock wave generated by high-energy explosives can splice two pieces of subcritical nuclear material together in milliseconds."

"Then, at the moment of merging, the ignition neutron source is activated, neutrons are released, and a chain reaction occurs."

In a gun-type atomic bomb, two pieces of nuclear material are placed at opposite ends of a steel tube, with high-energy explosives attached to the rear of the nuclear material.

After detonation, the shock wave causes the rear nuclear material to collide with the front nuclear material at a speed of 300 m/s, thus triggering the explosion.

This method is very similar to the process of propelling gunpowder in ordinary firearms, so it is named "gun method" or "bullet method".

The advantage of this method is that the structure is very simple, the technical threshold is very low, and it can be manufactured without even complex nuclear tests.

However, the drawbacks of the gun-type atomic bomb are also obvious.

First, its power has an upper limit.

The mass of the nuclear material at both ends must be lower than the critical mass.

In other words, the total mass of nuclear material in an atomic bomb is at most twice the critical mass, with the upper limit locked.

Second, the material utilization rate is extremely low.

Of the two nuclear materials, only 1.5% is capable of fission; the remaining material is blown away before it can react.

Third, the phenomenon of "premature combustion".

Both uranium and plutonium nuclei will spontaneously fission in their natural state, releasing neutrons.

Therefore, a coincidence may occur:

That is, before the two pieces of nuclear material come into full contact and before the ignition neutron source begins to emit neutrons, a chain reaction is initiated due to the spontaneous fission of the nuclear material.

This would greatly reduce the efficiency of the explosion.

Of course, this situation is very rare.

For this reason, the gun-type design is only suitable for uranium-235 and not for plutonium-239.

Because the probability of spontaneous fission of plutonium-239 is much greater than that of uranium-235.

However, at the time, the amount of uranium-235 was only enough to make one gun-type atomic bomb, and it was not possible to conduct a test explosion of this structure.

In other words, whether the gun-style method works or not needs to be verified.

Then, Oppenheimer waved his hand:
"To recreate a gun-type atomic bomb using plutonium-239, we must ensure the feasibility of using a uranium bomb."

Here you might be wondering:

"Didn't they say that the gun-type design isn't suitable for plutonium-239? Why are they still forcing it?"

The term "unsuitable" here simply means that the risk is high, not that it is definitely not feasible.

With Oppenheimer's firm order, the bigwigs in the theory department quickly came up with a solution.

They lengthened the steel pipe, which increased the distance between the two plutonium blocks.

Moreover, the plutonium block at the back end can achieve a higher speed after detonation, reducing the impact of spontaneous fission.

In the end, scientists created two gun-type atomic bombs, which were codenamed the famous "Little Boy" and "Skinny Man".

The latter is twice the length of the former.
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[Little boy]

Type: Gun-type uranium bullet;
Nuclear material loaded: 64 kg of uranium-235;

Dimensions: 3 meters long, 0.71 meters in diameter, and weighing 4.4 tons;
TNT equivalent: theoretical 2 tons, actual 1.5 tons.

Positioning: Combat missile, to be dropped on Hiroshima, the birthplace of the Sakura clan;
Skinny

Type: Pistol-mounted pistol bullet;
Nuclear material loading: 6.2 kg plutonium-239;

Dimensions: 6 meters long, 0.61 meters in diameter, and weighing 3.4 tons;
TNT equivalent: Theoretical 3 tons, estimated 5000 tons, actual 2 tons. (Far exceeding expectations)

Position: Test bomb;
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The boy had a total of 64 kg of uranium-235, but less than 1 kg of uranium-235 underwent nuclear fission.

Even less than 1g of uranium-235 is actually converted into energy.

The material utilization rate of the gun-type structure is indeed heartbreakingly low.

Otherwise, the Sakura Clan might have surrendered even sooner.

After the design principle of the gun-type atomic bomb was finalized, the project continued because there was still plutonium-239 left and it could not be wasted.

However, using plutonium-239 in guns still poses potential risks.

Therefore, Oppenheimer needed to design a new detonation structure for plutonium-239 to create another atomic bomb.

So he turned his attention to the second design option: the implosion type.

This is a precisely controlled centripetal compression detonation method.

Its core principle is:

“At the center there is a large mass of nuclear material below critical mass, and then an even number of small nuclei of nuclear fuel are uniformly surrounded around it.”

"Each small piece of nuclear fuel is backed by an equal amount of high-energy explosives."

"Then, the high-energy explosives are ignited at the same time, and the resulting centripetal shock wave squeezes all the small pieces of nuclear fuel to the center, where they merge with the large piece of nuclear fuel, exceeding the critical mass."

"Then the neutron source is ignited to release neutrons and initiate a chain reaction."

Because of its encircling structure, the implosion atomic bomb looks like a fat person with a large body and small feet, rather than a straight structure.

As can be seen from the principle, the implosion design is technically extremely complex.

Precise control of the detonation time and direction of small nuclear fuel pieces is required to form a uniform compression wave.

This process requires a large number of complex mathematical calculations, mainly various partial differential equations.

The saying "an abacus can produce an atomic bomb" is often heard in later generations, referring to these very things.

As mentioned earlier, both the United States and later China used computer computing.

Only a few key equations and parameters require careful manual verification; the abacus is not as useful as one might imagine.

Moreover, any change to any of the dimensional parameters requires recalculation.

For example, changing 8 small pieces to 10 small pieces increases the power of the atomic bomb, but changes the dynamic model of the small pieces.

In the theoretical department of Los Alamos National Laboratory, luminaries such as von Neumann, Taylor, and Feynman were responsible for this part of the calculations.

Moreover, the research team on implosion had as many as 600 members, which shows how difficult it was.

Although the design of an implosion atomic bomb is very complex, its advantages are also obvious.

First, the implosion design can be used for both uranium-235 and plutonium-239.

Because compared to the collision of two nuclear materials in a gun-type explosion, an implosion-type explosion requires several or even a dozen materials to collide simultaneously before it explodes.

Even if a part spontaneously splits, it will not affect the overall function.

Therefore, the "delicate" plutonium-239 can safely adopt this structure.

Second, the material utilization rate is high.

Implosion-type nuclear reactors can achieve a material utilization rate of over 20%, which greatly reduces the waste of nuclear materials.

Third, implosion-type nuclear weapons can be miniaturized. In gun-type nuclear weapons, the volumes of the two nuclear materials are mechanically added together, meaning that the critical mass is exceeded by increasing the amount of fissile material at normal density.

However, in implosion structures, due to the greater amount of high-energy explosives, higher pressure can be generated, and the density of nuclear materials can be further compressed.

According to nuclear theory, the higher the density of nuclear material, the smaller the critical mass. (This should be relatively easy to understand.)
Implosion-type bombs can be made with smaller yields, resulting in a lighter weight that can be mounted on missiles.

Therefore, in later generations, the implosion design became the mainstream design for atomic bombs, marking the beginning of the miniaturization of nuclear weapons.

Of course, what I've described above is just the most basic principle of implosion; the actual design is extremely complex and requires a great deal of knowledge.

To avoid being invited for questioning, I won't go into details here.

Once the principle was finalized, Oppenheimer had complete confidence in the implosion atomic bomb.

Groves asked him:

"What if the design principles of this atomic bomb cannot be tested?"

Oppenheimer said domineeringly:
"I guarantee with my integrity that the implosion method requires no testing and can be used directly in actual combat!"

Groves shouted "666" repeatedly.

Because he knew that even if he objected, it would be useless; the remaining plutonium-239 was only enough to make one implosion atomic bomb.

There are no materials left to conduct experiments.

He had no choice but to trust Oppenheimer and the wisdom of the more than 1000 scientists behind him.

And this atomic bomb is the famous "Fat Man" of later generations.
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[Fatty]

Type: Implosion plutonium bomb;

Nuclear material load: 6.4 kg of plutonium-239; (one-tenth the weight of a uranium bomb)

Dimensions: 3.3 meters long, 1.5 meters in diameter, and weighing 4.5 tons;
TNT equivalent: theoretically 3 tons of TNT, actually 2 tons of TNT.

Positioning: Combat missile, to be dropped on Sakura clan members in Nagasaki;
Thus, the Manhattan Project, which lasted three years and consumed countless financial and material resources, ultimately produced three atomic bombs.

The final step is the actual test explosion!

After extensive investigation, the site for the atomic bomb test was chosen to be the Alamogordo desert region, 200 kilometers north of the Los Alamos Laboratory.

This is a U.S. Air Force base, with a test range that is 38 kilometers long and 29 kilometers wide.

Because the test site was named the "Triad Test Site," this explosion was also known as the "Triad Explosion," codenamed "Triad."

On July 15, 1945, the day before the test, the "Skinny Man" was assembled and placed on a 103-meter-high iron tower, ready to be detonated.

Here are some questions you might have:

"Why not detonate it on the ground?"

This is because theoretical calculations show that an atomic bomb can only produce maximum destructive power when it explodes at high altitude.

The destructive power of the atomic bomb is mainly manifested in four aspects:

1. Shockwave: A wave of energy that is released in an instant and compresses the air.

2. Photothermal radiation: More than 50% of the energy of an atomic bomb is converted into heat and light.

3. Particle radiation: Various types of radiation, including alpha rays, beta rays, gamma rays, and neutron rays, are produced instantaneously and are extremely harmful.

4. Radioactive dust: Some radioactive materials are dispersed in the air in the form of dust. Due to their long half-life, they can continuously release radiation.

3 and 4 refer to what is known as "nuclear radiation".

If an atomic bomb is placed on the ground, the soil will weaken the destructive power of these four aspects, resulting in a significant reduction in its destructive force.

After all, no matter how powerful an atomic bomb is, it's not even a tiny fraction of the Earth's mass.

People in later generations often say that the combined nuclear weapons of the United States and the Soviet Union could destroy the world.

That's impossible. At best, it's just scratching an itch on the Earth; it can't even break through the surface layer.

Theoretically speaking, if an atomic bomb is placed on the ground and detonated, it can only create a crater at most a few tens of meters deep.

1945年7月16日凌晨5点30分。

The world's first atomic bomb, nicknamed "Skinny Man," was successfully tested in the Alamogordo desert of New Mexico!

Within a radius of 30 kilometers, the intense light was as dazzling as thousands of suns, illuminating everything in sight.

Then, a fireball with a diameter of over 300 meters slowly rose, changing from gold, purple, violet, and gray to blue.

A dozen seconds later, the fireball transformed into a mushroom cloud 12 kilometers high, a hallmark of an atomic bomb.

Oppenheimer, seeing the endless light and heat, couldn't help but say:
"I have now become death, the destroyer of the world."

"Damn it, now we're all sons of bitches."

Fermi calmly stated:
"In any case, this is a remarkable achievement in physics."

Feynman remained silent, simply reaching out his hand to feel the tremor of the wind.

"Nine-nine percent, a rare item. No, it's a Force 9 gale, 20,000 tons."

It is said that he accurately determined the explosive yield based solely on the strength and direction of the wind.

Of course, there's a strong suspicion that he's bragging.

The "31" experiment far exceeded expectations, proving the feasibility of the gun-type atomic bomb and marking the formal entry of human civilization into the era of nuclear deterrence.

1945年8月6日8点16分，美国向樱族广岛市投掷【小男孩】，完成人类历史上第一次原子弹实战。

But the Sakura tribe showed no fear; instead, they put up a stubborn resistance. The higher-ups lied and claimed it was a meteorite attack, urging the people not to panic.

Three days later, at 11:02 AM on August 9, 1945, the United States dropped the "Fat Man" bomb on Nagasaki, marking the second time in human history that an atomic bomb was used in combat.

The Sakura clan emperor was so frightened that he dared not surrender and immediately announced his unconditional surrender.

Because high-ranking military officials told him that the United States still has the capability to build 10 more atomic bombs.

The two atomic bomb attacks resulted in the deaths of hundreds of thousands of Sakura people, destroyed countless buildings, and dealt a blow to their arrogance.

When Einstein heard the news, he was completely devastated.

"If I had known that the Germans would not have succeeded in developing the atomic bomb, I would have done nothing."

Some people may find it strange:
Why was Einstein not involved in the entire Manhattan Project?

As the world's leading scientific figure, he should at least be appointed as an advisor.

This is because the U.S. military, after assessing Einstein's mental state, determined that he was an "extreme radical."

In modern terms, he was a "paranoid".

It is highly likely that Einstein secretly sabotaged the atomic bomb at the last minute.

However, the scientists in the theoretical department still did something similar.

Many people fear that once the United States possesses atomic bombs, it will dominate the world and become the sole superpower.

Therefore, they secretly provided the design data of the implosion atomic bomb to the Soviet Union through spies.

The attempt is to use a balance between the two to contain America's ambitions.

Therefore, the parameters of the first atomic bomb tested by the Soviet Union were almost the same as those of the "Fat Man".

Of course, they would never admit it.

Soon, humanity made tremendous strides in the research of nuclear weapons.

The atomic bomb, once regarded as the ultimate weapon, has become the lowest-ranking member of the nuclear weapons family.

(End of this chapter)