Little Boy and Fat Man

And while I could do an episode about Barbie, talking about, you know, some of the Barbie dolls and various toys that have crossed over into the tech sphere and some of the issues that those toys created, primarily regarding you know, privacy concerns, I thought instead we'd talk about the atomic bombs used in World War Two Batman and Little Boy, because you know, Oppenheimer was also a pretty big hit

at the box office this weekend. So in World War two, the United States dropped two different types of atomic bombs on the US hit Hiroshima with a bomb called Little Boy, and Little Boy used uranium enriched uranium as the fissionable material that would produce the intense energy of the bomb. And then the US dropped a bomb on Nagasaki. That one was called fat Man. Fat Man had a plutonium core, not uranium. But how did these bombs actually work well.

First of all, it boils down to atomic physics. So some heavier atoms are unstable, and you know, with the right instigating incident or with enough time, the heavier atom will split into smaller atoms and release neutrons. Also in the process doing this ends up also releasing a tremendous amount of energy. Splitting the atom is also called fission, and this is the type of technology our nuclear power

play rely upon. The big difference being that in nuclear power plants you have a controlled nuclear fission reaction and in a bomb, ultimately you have an uncontrolled chain reaction that releases a tremendous amount of energy. Now, you do get a whole lot of energy just by splitting one atom, but you could really get a big release if you were able to set up a chain of atomic reactions.

So how do you do that? How did the engineers and scientists who worked for the Manhattan Project, because that was the name of the project that developed the atomic bomb for the United States, how would they guarantee a chain reaction? Well, let's talk about those two elements that were used in each of the atomic bombs, or rather, you know uranium in Little Boy and plutonium and fat Man. So the type of uranium that little Boy used was uranium two thirty five. Fat Man was dependent upon plutonium

two thirty nine. Both of these are isotopes, and both of these isotopes regularly undergo fission. They are very much

ready to split apart with the right situation. Now, the way you start all that is that you shoot the isotope with a fast moving particle, essentially a neutron neutrally charged particle, sub atomic particle that if you were to shoot that at a uranium two thirty five atom and it makes contact, Essentially, the two thirty five would absorb that neutron and then the atom would split apart and in the process also release other neutrons, So that neutron

strikes the isotope, you get the split, you get more neutrons released. If you've got more atoms of that same heavy atom, like U two thirty five, packed together, then the release neutrons can make contact with those uranium atoms and then cause the reaction to continue. So you've got to pack enough of these atoms together to increase the chances of that happening. You know, keep in mind, like when we're talking about atoms like very very tiny stuff

and subatomic particles even tinier. You've got to pack a whole lot of it together to increase the odds of a neutron hitting an isotope. Otherwise, if it doesn't, if the neutron ends up being absorbed by something else or escapes or whatever, then it doesn't continue the reaction. You have to have it set up so it creates the sort of domino effect, except we're not talking on one

to one relationship here. It'd be a domino effect where you know, you have a domino that, when you knock it over, makes contact with two other dominoes at the same time, knocking both of those over, which in turn make contact with two other dominoes, and so on and so forth, so that by knocking one domino over, you'll ultimately knock over a whole bunch. Same idea here, except we're talking about isotops. We're talking about individual atoms and packing enough of them together so that you do get

this chain reaction. And once you do that and you have nothing there to rain in that chain reaction, you get a truly tremendous release of energy in the process. So again we use the same sort of process in nuclear power plants. But we have tools there and processes that allow engineers to control the sequence, this rate of release, and that way they can release enough in order to

generate electricity. So, in other words, they can allow this process to occur at a specific rate, and then the energy they release in the process they can use to generate electricity. I'm actually skipping a step here because the energy that gets released ends up essentially being incredibly intense heat, which you then use to turn water into superheated steam, use that to turn turbines which generate electricity. The steam eventually condenses down into water, and then that's in its

own closed system, and you just keep doing that. But in a bomb, you don't have these tools and processes to keep it under control. Right. You don't have a way of absorbing neutrons, for example, So the whole point is to get that uncontrolled chain reaction that, by the way,

is not a foregone conclusion. You can't really control where a release neutron is going to go, So again, you have to have the right amount of fissionable material in the right density, otherwise your bomb will only release a fraction of the energy you were planning on and you won't get the effect you were hoping for. It won't

be nearly as devastating. And the only reason to use a weapon as devastating as an atomic bomb or nuclear weapon is to convince an opponent to surrender, because it's just such a truly devastating weapon, and it's not like you can use it to target specifically just military installations for example. You're going to be taking out civilian sites and innocent people who are not soldiers. So it's a horrible, horrible weapon, and the only reason you use it is

to convince your opponent to surrender. Anyway, in order to do that, you have to make sure you've got enough fissionable material in your bomb, or else it's not going to have the effect you want and the conflict will just continue. So you have to reach what is called critical mass. This is the mass of fissionable material you

need in order to start a chain reaction. That mass is completely dependent upon things like how much volume the fissionable material takes up, which we'll talk about when we

get to the fat Man. So the more material you have, or the more mass you have, the greater the odds are that neutrons that get released in this reaction are going to hit another heavy atom, another heavy isotope, and you've arrived at critical mass when it's likely that a release neutron is going to create a subsequent heavy atom to split and release more neutrons. Now, finding out what it would take to achieve critical mass, that was a big part of the work over at the Manhattan Project

was to actually determine what that would be. How much enriched uranium or how much plutonium two thirty nine would you actually need in order to achieve this and have it be a chain reaction that actually works. So Oppenheimer and others, he wasn't the only one, obviously, this was a huge team of scientists and engineers who worked on

the Manhattan Project. They were trying to develop a weapon that could initiate an atomic reaction that would rapidly consume a core of heavy atoms to generate an enormous destructive wave of energy. That was the whole goal, and they came up with two different ways of doing that using the two different elements of you know, uranium two thirty five in one case and plutonium two thirty nine in

the other. So first we'll talk about uranium two thirty five, also known as refined uranium, because most of the uranium we encounter naturally on Earth is a totally different isotope. It's not you two thirty five, it's uranium two thirty eight. And you might wonder why does that make a difference, Like why is one type of uranium useful for weapons and the other one isn't. Well to do that, we

have to talk about isotopes. So an isotope is just a form of an element, right, you have, and when you're talking about isotopes, you're talking about two or more forms of the same element. Each isotope of an element will have the same number of protons as all the other isotopes of that element, right, because if you were to add or subtract protons, you would change the element itself. It would no longer be the element you started with.

So the number of protons remains consistent across all isotopes. The difference is in the number of neutrons that are in the nucleus. So uranium two thirty five has one hundred forty three neutrons in its nucleus. Uranium two thirty eight has one hundred forty six neutrons, And this might lead you to say, well, neutrons are neutrally charged. That's why they're called neutrons. They have a neutral charge. How does that make it a difference, Like, what difference do

three neutrons make? Well, isotopes can actually have different chemical properties from one another, which is kind of crazy, right, You're talking about two things of the same element, but they can have different chemical properties. So uranium two thirty five and uranium two thirty eight are both isotopes of uranium, but they don't always behave the same way. So let's take uranium two thirty eight. Now, I mentioned that to initiate nuclear fission, you would fire a neutron at an

isotope and it would split that isotope up. But if you were to fire a neutron at uranium two thirty eight, instead of splitting up, it could just capture that neutron and become uranium two thirty nine. So instead of two thirty eight, you got two thirty nine, but you don't get that split. And that means that if uranium two thirty eight absorbs the neutron and becomes uranium two thirty nine,

there's no chain reaction because it didn't split apart. It didn't release more neutrons to cause that reaction to continue. So your reaction would go nowhere. You would just have uranium two thirty nine now, and that wouldn't do you any good. You wouldn't have an explosion. Uranium two thirty five is a totally different story. If you fire a neutron at uranium two thirty five, you're gonna get an atomic split and a whole butt load of energy in

the process. But here's the thing. Uranium two thirty eight, that's the stuff that's abundant. That's the stuff we can find naturally on Earth. Uranium two thirty five makes up less than one percent of naturally existing uranium, which meant the scientists had to develop a means to refine uranium two thirty eight into uranium two thirty five. All Right, we're going to take a quick break. When we come back, we'll talk more about the challenges that the engineers and

scientists of the Manhattan Project were facing. We're back now. During the Manhattan Project, obviously time was ticking. This wasn't some R and D project that could just take as much time as necessary. There was actually a war on there was a concern that access nations could be developing

their own atomic weapons. So the United States poured a lot of resources into this research, and the desire was to find a process that would work, and it didn't matter which process it was, So actually the Manhattan Project was pursuing different strategies simultaneously. One of the overseers of the Manhattan Project was General Leslie Groves, who authorized four separate projects to explore how to refine you two thirty eight into You two thirty five. And again they wanted results.

They didn't really care which one was going to be the best. They just needed that uranium. So the scientists already knew that standard chemical processes were not going to necessarily work to refine You two thirty eight into You two thirty five because the two isotopes, while they are different, share enough chemical similarities that it just wasn't going to be a way forward. So instead they looked at methods that included liquid thermal diffusion, gaseous diffusion, separating the components

with the centrifuge, and electromagnetic separation. I should probably do an episode really that really focuses on those four specific approaches, but for the process here, it just meant that they were able to generate enough you two thirty five to make a viable weapon. So they finally got enough fissionable material to construct a bomb. They did a test bomb, obviously, but they also put together Little Boy. This bomb worked on what was called a gun type device inside of it.

The bomb itself had a bunch of different elements so that it would explode the way the engineers intended. That is, it would explode in the air. This was not a bomb that was meant to collide with the ground and then explode. That would have limited its destructive capacity. So instead, the engineers designed it so that at a specific altitude

it would initiate the explosion. So to achieve this, the bomb actually had several systems on board to measure when to ignite its explosive charge that would initiate the nuclear reaction inside the bomb. So the explosive charge wasn't the bomb itself. The explosive charge was kind of the trigger to start the nuclear reaction, which then would release the

truly enormous amount of destructive energy. So the tools they used in order to measure altitude for the bomb so that it would go off at the correct height above the target. Included barometric press sensors. Those measure barometric pressure, so they would essentially monitor for the pressure to reach a point that would indicate that it was at the

right altitude. But they also had radar altimeters on this bomb, and they were essentially shooting down radio waves toward the ground and listening back for echos, And when those echoes would indicate that the bomb was at the proper altitude, then it would trigger the explosive, the conventional explosive that

would then lead to the actual nuclear reaction. So if you were able to look inside the Little Boy bomb, you would see that the conventional explosives were at the tail end of the bomb, and they would end up driving forward some thick disks of uranium two thirty five. So these disks, you know, they had a hole in the center of them, and they were at the tail

end of the bomb. Like I said, the explosive would go off, it would end up propelling these discs forward toward the nose end of the bomb, just like a gun would propel a bullet, Like you know when the gunpowder inside a cartridge would ignite the gases expanding would push the bullet through the barrel of a gun, similar in that case, except there's no open end of this gun, So this stack of thick disks would shoot forward. On

the opposite end of the bomb. In the nose end of the bomb would be a stack of uranium two thirty five that were at the diameter, so they would fit inside those thick disks. So what happens is you've got these two halves of a core essentially that came together, and now you suddenly had this solid core of uranium two thirty five. Also, there was some polonium inside this bomb. The polonium would actually act as the release of neutrons

that would start the whole reaction going. So the conventional explosives were necessary to get the kinetic energy that would then launch this nuclear fission process that quickly became an uncontrolled chain reaction and would release an enormous amount of energy. In total, the Little Boy contained sixty four kilograms of enriched uranium. That's a lot of uranium, and the explosion

it generated was the equivalent of fifteen kilo tons. So when you hear explosives being talked about in kilotons or megatons, whatever it may be. That's actually talking about how many tons of TNT it would take to get an equivalent release of energy. So fifteen kilotons means you would need

fifteen thousand tons of TNT to get the equivalent explosion. So, yeah, you had this bomb that at the right altitude would have a gunshot essentially go off inside the bomb, the two halves would come together, some neutrons would get released, the nuclear reaction would immediately follow. You would get an instantaneous,

uncontrolled chain reaction. And this truly tremendous amount of energy released overhead of the city because again they thought that if they could release the energy in the air, they would cause way more damage. It's hard to get your mind wrapped around how much damage you're talking about. At ground zero, where Little Boy exploded, there was a zone of around like zero point thirty six square kilometers that

was just totally devastated. That was total, total destruction. Buildings were leveled, Any buildings that were remain standing had such structural damage that they were unstable. It would be possible to have survived in that blast zone initially anyway, if you were in a truly strong, stable structure underground really, so like if you were at the bottom of a really solid parking deck that wasn't just completely crushed by the energy of this explosion, you could have survived the

initial blast potentially. However, there would be other issues, like the intense amount of radiation would certainly cause problems that wouldn't be just the concussive force of this energy radiating outward. So yeah, pretty much at ground zero, you would have people who likely would not survive either with the structures. Beyond that, you would have a zone that would be called like a moderate damage zone that could extend out to a radius of around a mile or one point

six kilometers from the point of detonation. Here you would still have substantial damage to structures. Some of them might remain standing, but a lot of them would be leveled. And depending upon where you were at the moment, and if you were in a stable structure, you might have made it through. You might have survived within that moderate zone, but you would likely be in need of urgent medical

attention due to other things. Like you got to remember, this explosion, it would create a like a fire ball or a wall of fire really that would extend out very quickly, and it was intense enough to vaporize you if you were just outside. I mean, it was incredibly intense energy. Beyond the moderate zone, then you have the light damage zone. This could extend ten miles out from ground zero. And even in this light damage zone, you could have, you know, an increase in air pressure that

would cause all the windows to shatter. From there, you know, you might have more or less superficial damage from the actual physical blast, but again you still have the issues with radiation, and obviously the damage would create other problems, like you would get fires, and it would wipe out utilities. Truly devastating weapon. I know I'm using that word a lot, but I can't think of a word that's more fitting. Now. It's actually really hard to estimate how many people died

from the detonation of Little Boy. There's a pretty huge span of estimates here, Like on the low end, on the low end of estimates, it's around seventy thousand who died as a result of Little Boy exploding. On the high end, you're talking one hundred and forty thousand, twice as many. It's a really tough question to answer. For one thing. Japanese authorities didn't have a really good handle on how many people were living in these cities in the first place, so it's hard to say, you know,

how many people were missing afterward. And then they're also tougher parts of the question, like do you just count the deaths that happened as a result of the initial blast or the fires that were produced as part of it, What about other hazards that were more long term, where you know, it wasn't initially from the explosion, maybe it was in the hours or days or weeks that followed it, or if you're talking about radiation, what about the months

or years that followed. So it does make it very, very very hard to estimate the number of deaths, but clearly it was in the tens of thousands, and potentially well over one hundred thousand, just or Hiroshima. All right, we're going to take another quick break. When we come back, we'll talk about fat Man and Nagasaki. Okay, So I had mentioned that Little Boy used enrich uranium as its

fissionable material. Fatman used plutonium, and this meant that the method that Little Boy used to initiate that nuclear reaction, that gun method wouldn't have worked with fat Man. It would actually have caused the bomb to undergo spontaneous vision before the gun mechanism could even fire, which means the bomb would lose a lot of its energy before it

could even explode. So again, you wanted to maximize the effectiveness of this weapon, or at least that's what the scientists and engineers wanted to do, because the whole purpose was to create a weapon so terrible that your opponent surrenders rather than risk being hit by it again. So the team had to come up with a different way

to have the mechanism explode. So one of the problems that they faced was actually that they needed to use plutonium two thirty nine, but their reactors couldn't create pure plutonium two thirty nine flawlessly. They kept creating trace amounts of plutonium two forty and plutonium two forty that isotope is more prone to spontaneous fission than plutonium two thirty nine. So what they needed was they needed a way to

have a subcritical mass of plutonium. They needed it so that it would not spontaneously undergo fission because the atoms would be too widely spaced apart so you needed to be subcritical until the moment when you needed to initiate the nuclear reaction. Then you needed to somehow make this subcritical mass become a critical mass. So their approach was to surround a subcritical plutonium core with essentially a globe of conventional explosives. So think of like, you know the

Earth has an iron core. Well, this was a explosive globe with a plutonium core. And the conventional explosives were designed so that they would ignite simultaneously and they would explode and collectively create this tremendous pressure on the plutonium

core in the center implosion. In other words, that would end up squeezing this plutonium core and increasing its density, and that is what would push the plutonium core from being subcritical to critical by essentially physically squishing all those atoms closer together. Now, your subcritical plutonium mass is a critical plutonium mass, and that means that once that nuclear fission reaction can start, you've got yourself your chain reaction. Now,

this was a really efficient weapon. It was much larger than Little Boy because you needed way more conventional explosives. Right, the gun method only needed a relatively small amount of conventional explosives to bring the two halves of the uranium core together, but the fat Man bomb needed a lot more conventional explosives to create that concussive blast that would create the implosion. So the Fat Man was much larger than the Little Boy, but it needed less fissionable material.

You know, the Little Boy needed sixty four kilograms of uranium two thirty five. Fat Man only needed six point four kilograms of plutonium. And while the Little Boy bomb produced a fifteen kiloton explosion, fat Man yielded a twenty one kiloton blast. So not only did it require less fissionable material, it had a larger energy output. Despite that more powerful blast, the estimates of casualties and not Kasaki

are much lower than for Hiroshima. Still, we're still talking tens of thousands of people, so I don't want to suggest that it wasn't many. It was a lot, It just wasn't as many as what we saw in Hiroshima. So on the low end, we're talking around forty thousand people killed by this bomb. The high end puts that at seventy thousand. So if we add both of those events together, then the estimate of deaths ranges from one hundred ten thousand on the low end to two hundred

ten thousand on the high end. The demonstration of such destructive power was more than effective enough to force Japan to surrender, because really, think about it, these were just two attacks, and they were just carried out by two bombers, and those two bombers killed more than one hundred thousand people at the low end of estimates. That is a truly grim kind of evidence to show that weapons capabilities.

And it would mean that if you know, if you extended that and you thought, well, what if an entire fleet of bombers were to fly over a country carrying lots of those bombs, think of the devastation that would mean, Like, you have no choice but to surrender. That was the thought process, and it's exactly what did happen. But it also launched countless debates about whether or not the US was justified in using such incredibly powerful and deadly weapons

in an effort to end the war. Like the argument was, if we don't use the weapon, the war continues, and who knows how many people die. If we do use the weapon, a whole bunch of people die, but the war ends. Like it. It's a really tough dilemma that I cannot easily dismiss. I mean, I certainly am anti bomb. I am not pro bomb even in the slightest But at the same time, it is very hard to figure out what's the right approach if the opponent is not

already leaning towards surrender. And this conflict could go on indefinitely, which means that the number of casualties is impossible to calculate. It does get very hard. Oppenheimer himself was obviously deeply conflicted over all this. On the one hand, he and the team at the Manhattan Project had really cracked technical and scientific challenges that were standing in the way of creating an atomic or nuclear explosion. This was never a

foregone conclusion. It was a really challenging thing to do, and they were able to achieve an incredible advance in science and technical ability. But on the other hand, the devastating effects of the bomb weighed heavily on him. He very much struggled with the knowledge of how many died as a result of the explosion of those bombs, and

it led to him opposing nuclear development and proliferation. He foresaw an era of nuclear proliferation, in which you know, countries would be compelled to develop nuclear weapons in a way to act as a deterrent and protection against nuclear

capable countries, and in fact, that is what happened. And for those of you who are around my age or older who remember the Cold War and the age of nuclear proliferation, there was just this sort of constant, ominous possibility of nuclear conflict that hung over us, that made its way into pop culture entertainment, and it was something that people would occasionally talk about and probably not talk about for too long because it was very disturbing. But

that's exactly where we went. It's where Oppenheimer kind of assumed the world would go, in that you had to develop this weaponry in an effort to protect yourself against

those who already had it at their disposal. And then you had this sort of concept of mutually assured destruction where a nuclear capable country could assure that it would be able to destroy another nuclear capable country if nuclear war were to happen, which theoretically would prevent nuclear war from ever happening, because to initiate nuclear war would mean you would know that you were you know you were

committing your entire country to destruction. So not a cheerful way to approach conflict resolution obviously, and also not always an effective way. We saw something very similar happen with conventional war and leading up to World War One, and it didn't work because people's you know, these countries started to develop very powerful militaries with the thought being that that would dissuade any kind of war within the continent of Europe, and of course that that's not what happened.

So very scary. Also, I think it's relevant today because not only do we still have to worry about nuclear weapons, but we also have been talking a lot about AI and how AI has become kind of another arms race, and that there's this concern that even if a country decides specifically to stay away from incorporating AI into military processes and equipment and strategies, some other country may not have that reluctance, And so if they do that, could

they end up having a military advantage? And can a country afford to give other countries that military advantage, which then drives the need to you know, embrace AI everywhere. And we've already seen that that can be a really scary thing. So yeah, I think Oppenheimer is just as relevant today. Like I think that his story and the story of the Manhattan Project and the conflict within the teams at Manhattan Project, I think it's still very much

relevant today. We're seeing the same sorts of discussions and debates play out in the AI space, and yeah, it's scary stuff. It's scary and it's not easy. Like again, I am personally anti like weapons that kill lots and lots of people, especially people who have no direct connection with conflict. I'm very much against that. But I also can't pretend like I have the solutions that would lead to everybody joining hands and singing songs unless it really

is as simple as buying everybody a coke. I was taught in the seventies, and that's all it takes. I remain skeptical, but I have to admit I haven't tried it because I don't I don't live in that tax bracket. But if I ever do, I'll give it a shot. It's got to be better than developing massive weapons. I hope you were all well, I'm curious how many of

you went to see either Barbie or Oppenheimer. I haven't made it out to either, not because I didn't want to, but because when I started to look for tickets, I couldn't find seats together in a place that wasn't way off to the side or way in the front. And I go to so few movies. I just can't. I can't put myself in a position where I'm gonna get a terrible crick in my neck trying to watch a film. So I'm waiting a little bit longer so i can

see I am playing seeing both of them. By the way, I have a desire to see both of those movies. But if you did see them, I'm curious what you thought you can reach out to me. We still have a well, I guess now it's an x account. Used to be called Twitter, but Elon must change that to x. I'll talk about that more tomorrow. That's called tex stuff HSW If you want to send a message there, although I may not even see it because it's hard for

me to log into that account. Now, you can just tweet at me or x at me whatever it's called now. My handle is John Strickland. That's j o En Strickland. But you can also find me on threads and if you're on Blue Sky. You can find me there too, John Strickland and all of those. And hope you're all well, and I'll talk to you again really soon. Tech Stuff

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