Nuclear 101: How Nuclear Bombs Work Part 1/2

Well, welcome and thanks for tuning in online, today we're going to talk about the basics of

nuclear

weapons before we get to that, although I wanted to mention a couple of books first for those who want to go into more detail, if they really want to. I want to understand the physics of

nuclear

weapons. The Los Alamos manual is an amazing document. These are the lectures given to scientists as they arrived at Los Alamos for the Manhattan Project around 1943, with many additional notes and information of the kind. who gave the lectures really gives you a good introduction to the physics of nuclear weapons as it was understood in 1943 with some updates in the notes if you want a wonderful and gripping historical account of how nuclear weapons were created in the Manhattan Project.

The Making of the Atomic Bomb by Richard Rhodes is really a classic, I think it is understandable to everyone and yet it gets the physics more or less correct if you want a more technical description of the critical assembly of the Manhattan Project by Hottes and Henriksen Mead and Westfall. much drier than the manufacture of the atomic bomb but much more detailed on the technical front about the effects of nuclear weapons. The US government textbook on that topic written by Gladstone and Dolan is called The Effects of Nuclear Weapons and it is still available and in fact has been Put it online in PDF format if you are looking for it and if you want a detailed description of the impact of the bombings of Hiroshima and Nagasaki, there is a book called The physical, medical and social effects of the atomic bombings that is really a good

work

.

That said, let's get started first of all just to remind ourselves what we're talking about. This is an image of the Trinity test, the first nuclear explosion. I was a huge ball of fire, unlike anything that had been seen before on Earth. Today we are going to talk about how nuclear

bombs

work

ed. Fish infusion. The different types of nuclear

bombs

. We are going to talk about nuclear materials that can be used to make nuclear bombs. Let's talk about the hard

part

s. are about making a nuclear bomb and we are going to talk about the effects of nuclear weapons, okay, so it all starts with the splitting of atoms and there are some types of atoms that are large and difficult to handle, uranium-235, plutonium- 239 are the main ones that, if you hit them with a neutron they will start to oscillate and they will oscillate with enough energy sometimes that they fall a

part

into two smaller atoms, they split in half, okay and when that happens, the two smaller atoms don't They are stable with the number of neutrons that the original uranium or plutonium has.

The atom had and therefore also typically releases two or perhaps even three neutrons in this reaction. Now, if a large atom has a large number of positively charged protons and uncharged neutrons, they are held together in a big ball in the nucleus. now there are protons, since they all have a positive charge, they repel each other, okay, like the charges repel each other, now what holds them together are the nuclear forces, the strong and weak nuclear forces, and including those neutrons, they are like a glue that holds the core together, but once it splits. You have two halves, each with a lot of positive charge, so they separate at extreme speeds and that is where a large part of the energy that is released in a nuclear reaction comes from, which is actually the kinetic energy of their movement that is called fission products, the fission products, when that atom splits and you get a lot of energy from this fission reaction, you get around 200 million electron volts, which is a very approximate number, a little more for some and a little less for others. from each of these fish now that is more than a million times more than what you get from each atom that participates in a chemical reaction why chemical reactions only affect the electrons that are in a haze around the nucleus of the atom If this is the nucleus of an atom, then the electrons are here somewhere and over there somewhere, so they are much more loosely bound.

These nuclear forces are much stronger holding that atom together, so when it splits it releases this enormous amount of energy. a million, 10 million times more than the typical chemical reaction of a conventional explosive and that is why so much energy can be obtained from a bomb, that is why a bomb from an airplane can destroy a city instead of hundreds of airplanes dropping thousands of bombs. returning again and again as happened with other cities in World War II. Similarly it can also provide power for civil power generation with a lot of power coming from a small amount of material in a small space just to give you an idea if you have a 1 gigawatt coal plant you need an 80 car train full of coal every day to provide fuel, if you have a 1 gigawatt nuclear plant you need about half of one of those railcars once a year, a huge difference, so almost everything related to nuclear weapons. and about nuclear energy it arises from this basic technical fact: much more energy is obtained from each unit of material that participates in the reaction than in the case of conventional reaction.

Thanks, okay, but although that is a lot of energy per atom, it is Still, an atom is very small and still has a very small amount of energy, so it is necessary to form gigantic amounts of atoms to obtain a significant amount of energy. So how could that happen? How could you get a large number of atoms? split everything at once and the key is the notion that one neutron starts the reaction, one neutron splits an atom and then the splitting of the atom releases two or maybe even three neutrons and that's what means you can have a reaction in chain, you can have enough of one atom leads to enough of a couple more atoms which leads to the fission of more atoms and so on, so here we have a picture of fission occurring in a group of atoms that do not It is enough to start that type of chain reaction, it is not enough for a chain reaction that is sustained it is called subcritical less than critical critical is when the nuclear reaction can be sustained for a long time supercritical is when it grows exponentially as you want in a bomb nuclear, so what's happening here is a neutron is coming in and it hits an atom and that releases a couple of neutrons and one of those neutrons hits an atom but the other one flies out of the group of atoms and if that continues to happen the reaction it will stop because you will run Without neutrons and you will not have this continuous and accelerated chain reaction, so the question is if I want to make a nuclear bomb, how do I solve that problem?

How do I deal with the fact that my neutrons are leaking out of the system? stop the reaction, well there are actually several ways that people have thought about how to solve that problem, actually three ways, so the solution is to add more material. Well, here I have a larger group of plugins and you can see that in most cases the neutrons hit other atoms before some of them fly off into the surrounding field, but usually they hit other atoms first and that will lead to a continuous nuclear chain reaction, so a basic concept worth remembering is what is called critical mass.

Critical mass is enough nuclear material to sustain this type of chain reaction. Another idea is to reflect the neutrons again, so here I imagined the atoms in a box and the neutron and with it there is a perfect neutron reflector. There is no such thing, it is a perfect neutron reflector, okay, but there are things that will reflect neutrons more or less well, generally things that are found among atoms that have many protons and neutrons in their nuclei and that atoms heavy tend to reflect. Neutrons are better, but some of the lighter things can also reflect neutrons, so obviously if fewer neutrons come out because they are reflected, less material is needed before the reaction can be self-sustaining, so the reaction can be reduced. amount needed for critical mass by having a neutron reflector, another idea is to take this group of atoms and squash them together to make it denser, okay, the atoms are closer together, that means that when one of them releases a pair of neutrons, It is much more likely that those neutrons will collide with another atom before they escape from the system.

Now these three solutions have enough material that reflects the neutrons and crushes the neutron, squashing the atoms so they are closer together or often used together instead of just separately so that you can imagine what you want ideally is if you want having critical mass with the least amount of material and material is expensive to produce and difficult to produce, as we'll talk about, so you want to use the least amount of material as possible. You can and usually having it in a sphere is a good idea because if it's in a flat shape then there's a lot of opportunity for neutrons to escape.

If it is in a sphere, it is the minimum surface area for those neutrons to come out. When describing particular types of nuclear material, you will often see a phrase that is the critical mass of the bare sphere, so it indicates how much of a critical mass it needs to have if it is in a sphere and if the sphere does not have any neutron reflectors behind it. around. Okay, so remember the idea of ​​a naked sphere of critical mass. Okay, yeah, what will happen when this chain reaction starts? What happens is that this energy is released and released incredibly quickly.

These reactions take place at x, measured in billionths of a. Second, in fact, during the Manhattan Project, scientists invented a new unit of time, a jolt. You already know the expression two shakes of a lamb's tail, which refers to a very short period of time. One jolt is equal to ten billionths of a second and that's the time frame for good fishing, so what's happening is you're releasing all this energy into a pretty small ball of material and that means the material is going to heat up, turn into a gas. and will begin to explode if the atoms come close to crushing them.

By increasing its density, the amount needed for critical mass is reduced. Making them expand increases the amount and causes the neutrons to start flying into the surrounding field again and stops the chain reaction, so the key and difficult part of making a nuclear bomb is figuring out how I can put my material together to give it the shape I want it to be in order to get a good explosive performance before it starts to explode because one of the key things to understand about these materials is that sometimes they produce what is called spontaneous fission on their own and release neutrons, so So there are always some neutrons around, so you can't leave nuclear material in a supercritical form because it's going to start exploding, so the key problem is how to do it.

I gather the material in the way I want, in a way that is truly supercritical, that goes far beyond what is needed for a self-sustaining chain reaction, it will give me an increasingly explosive chain reaction before it starts to explode. Well, that's the key problem. gather the material quickly enough, so there are two ways that people have thought of to do this, basically one is what's called a gun type bomb and that is literally slamming two pieces of nuclear material together at high speed, yeah , if I had, for example, two-thirds critical mass of highly enriched uranium on this end let's pretend I'm strong because that would be quite a lot of material and two-thirds critical mass of highly enriched uranium in this hand and I played them there with my hands as fast as I can put them together with my hands that wouldn't give me a good nuclear bomb why because when they got maybe somewhere around here they would be close enough that together they formed a critical mass and as soon as a loose neutron started a reaction would start working and the uranium would melt into gas and be destroyed before it could get any significant nuclear yield.

Everyone in this room would be dead. I would certainly be dead. would have a tragic accident, but we don't want him to know that many city blocks were vaporized in a nuclear explosion, so the way a gun-type bomb works is to hit those pieces much faster than I could do it with my hands The bomb that leveled the Japanese city of Hiroshima was literally a cannon that fired one piece of highly enriched uranium at another piece of highly enriched uranium, so these are simple and reliable types of nuclear weapons. The United States never bothered to test the Hiroshima bomb before using it because it was so obvious that it would work and the basic idea of ​​the Hiroshima bomb was worked out by a professor and two of his graduate students in the summer before everyone arrived.

Los Alamos, so this isn't something incredibly complicated, unfortunately it can be done with a gun. bomb type good performance can only be obtained with highly enriched uranium good performance cannot be obtained with the othernuclear material that we're going to talk about, which is plutonium, why, because plutonium falls apart much more than highly enriched uranium, there's a lot of neutrons flying around when you have plutonium, even if you have pretty good plutonium and so So when the two pieces are joined together into a gun type bomb, even fired from a cannon, they will start fishing before joining together in the full configuration that what you want is not to get a Hiroshima scale nuclear bomb, try to make a bomb gun type with plutonium so you can only get high yield with highly enriched uranium, okay, so if what you have is plutonium or if what you have is not highly enriched enough uranium for a gun type bomb because remember those bombs Weapon type bombs are very inefficient, so what you use is an implosion type bomb, so this one is about crushing that nuclear material at a higher density.

These are much more efficient and therefore need less nuclear material, so To give you some rough numbers, the Hiroshima bomb, which was an inefficient weapon type bomb, had around a little over 60 kilograms of 80% enriched material, meaning 80% of the material was uranium-235 as opposed to of uranium 238, which has three more neutrons, which is the other type of uranium found in Iran that is extracted from the ground. Next time we will talk about how highly enriched uranium is produced. and plutonium and we will talk a little more about the different types of elements that are called isotopes which are things that have different numbers of neutrons in the nucleus an element is defined by the number of protons it has in the nucleus and the isotopes of an element such as uranium 235 or uranium 238 are the numbers 2, 35 to 38, they are the number of protons plus neutrons in the atom.

Well, back to the implosion type bomb, so here we have an image that shows the nuclear material surrounded with some of the other things that I'll talk about in a moment and then surrounded by explosives and a lot of the explosives are cut out here so you can see what the assembly looks like right now, what you need to do in this situation is what you need Detection of the explosives at exactly the same time around this bomb because if the explosives on this side explode first before the explosives on the sides explode what What you will have will not be a flattened ball but a pancake and remember that in a pancake the neutrons are escaping everywhere so what you want is a flattened ball which means you need the explosive shock wave to be a shock wave spherical that goes inward, so that is significantly more complex to design and build and would be much more difficult for terrorists. although it is still conceivable, especially if they had expert help and there are some approaches that are significantly less complex than the Nagasaki bomb.

I can't say much more than that in this unclassified talk, so most approaches require blast lenses and required millisecond timing. multiple detonations is somewhat complicated but, as I say, there are some approaches that are less complex. Well, let me talk a little bit about the evolution of implosion bomb designs because they have changed over the years. Well, then the Nagasaki bomb was a solid solution. ball of nuclear material, okay, the Nagasaki bomb was different from the Hiroshima bomb, which had about 60 kilograms of highly enriched uranium. The Nagasaki bomb had about six kilograms of plutonium, now plutonium is about three times more reactive than highly enriched uranium, so even if they were identical bombs it would have needed three times less plutonium, the reason why it needed ten times less is because I had the implosion device instead of the gun type device and the implosion is much more efficient, so you have this solid ball of about six kilograms of material, a ball that fits in my hand I will show you a picture on a minute and about had some heavy stuff for what's called tampering, so tampering does two things, firstly, it's the neutron reflector that reflects those neutrons and the way I talked about before, but secondly, if If you think about it, you would like to find a way to prevent that material from falling apart for at least a little longer and if you think about it, even a small amount of time could help a lot, why?

Because in one of these reactions in chain that grows exponentially, let's say it had them, let's say it was doubling each generation of neutrons, so an atom splits releases two neutrons, each of those splits, two more atoms release two more and so on, then the last generation of neutrons in that case would be giving it a large portion of all the energy you were getting, so if you can keep it from falling apart long enough for one or two more generations of neutrons to occur, you can get a substantial amount of performance now, so we'll give you an idea. let's put our steel cage around the thing, hold it turns out there's no way you can hold this.

You have a ball that is about this size where as much energy has just been released as 10 or 20,000 tons of conventional explosives. the ball has turned into gas and that gas has an incredible temperature and pressure, billions of degrees, incredible pressure, okay, and that ball will fly away no matter what you do about it, okay, there is no steel cage nor any material, titanium, whatever it may contain. that ball doesn't fall apart into black if you have too much fun, then the inertia it has to move those heavy things to explode and that could slow it down again, we're talking billions of seconds here, could slow it down enough to give enough additional growth in the neutron population to have a significant amount of additional energy release, so almost every nuclear bomb you'll see will have these things rigged, okay, so you'd have conventional explosives.

Okay, in these exploding glasses, okay, yeah, so things have evolved since the first generation and one thing that people thought about is let's not have a solid ball, let's have a hollow ball. Okay, a hollow ball of nuclear material. Because? Because when the explosives crush it, it begins. Since this part is nowhere near that part, it starts out pretty far from critical mass when the explosives crush it, it doesn't become critical mass until it's all crushed in the middle, that's fine, and it's a lot easier for the explosives to crush. at high speed because there is a large empty space in the middle.

Okay, that was the first step in evolution. Another good step in the evolution was to create an air space between the explosives and the ball in the middle. You still have manipulation, but it has an air space between the explosives and the ball, which is why it is sometimes called a levitated pit. This ball of nuclear material in the middle is called the well of a nuclear weapon. Now why would you want an air gap? Well, think about this when you hit a nail again, would you like the hair to be right in contact with the top of the nail and just press down on the nail?

No, you won't get anywhere with that, what you want to do is pull the hammer back and weigh. That now gives the hammer enough time to accelerate before hitting the nail, so here the explosives accelerate through the air gap before hitting the nuclear Mottola. Turns out it crushes the ball much more efficiently if you do that, okay, yeah, then came the really big thing. evolution, okay, so we had hollow balls, we had levitated balls, okay, now we're going to put something else in the ball, okay, you put a little tube in the ball and you put some tritium in it, it's a hydrogen atom with two neutrons and one proton, okay, it is known as Tritium, if it has only one neutron with the proton, it is known as deuterium.

So what happens is when the fission reaction occurs and you have this little ball heated to billions of degrees. That will cause a fusion reaction in this tritium. The fusion reaction will do two things: it will release a lot of energy and it will release a lot of very fast neutrons that will catch more nuclear material. Okay, so you understand that this is what is called a powered weapon. This is not real yet. hydrogen bomb but it's what's called a boosted weapon fission is being powered by fusion okay so every modern thermonuclear weapon in the US nuclear arsenal in the Russian nuclear arsenal is a boosted weapon like that okay yeah Come on, I apologize.

Let's move forward now, we're going to get really complicated for a minute because we're going to talk about modern thermonuclear weapons and you know, nuclear weapons designers have been creative over the years and things have gotten complicated, but let me try to go over it for a minute. moment. minute here, okay, so start with the primary, also known as the pet, okay, that's the same thing we were talking about, so it's a hollow shell of nuclear material that has some tritium inside of it, okay , then the explosives explode and crush him. ball, the fission reaction starts, you also have what is called a neutron generator in the middle of that ball that triggers a shower of neutrons at the right time so that your nuclear reaction happens at the time you want it to be right for that your fish and The reaction is activated, a fusion begins with the tritium that is in the middle of the well.

Well, tritium makes something more efficient happen. So few sufficient causes cause fusion and then fusion causes more efficiency. Okay, so that well releases a lot of energy. that energy is concentrated in what is called secondary, the secondary will usually have lithium deuteride, so that is the fusion fuel, deuteride means it has deuterium that is in a chemical bond with this lithium, lithium is actually It separates all this energy and provides tritium. that deuterium can fuse, okay, so you have this energy from the fission and fusion of the boosted pet that then focuses on the secondary and actually crushes the secondary with radiation pressure, believe it or not, it is the pressure of a very high frequency gamma light.

X-ray rays which are actually like a hammer crushing the secondary and heating it up, so you have these incredible pressures and temperatures in Andheri which then lead to fusion in the secondary, which releases a huge amount of energy and also releases a huge rain. of neutrons and so the designers thought well, if we have another big neutron shower, let's put in some nuclear material and we have something more efficient as a result of those neutrons, then what do you have? You know, this is this, stay with me for in a minute you have fishing which starts the whole thing, fusion which drives that fish and more, all of that then causes fusion, which then causes more fishing, so you have a fission reaction. , fusion, fission, fusion and in the end you end up with a typical bomb. of course, half the energy comes from fusion, half comes from fishing, the designer can change those proportions considerably, no one has managed to create a fusion bomb that doesn't have a fission bomb, he should blow it up.

The nasty radioactive fission products that create fallout and things like that come from fishing, they come from the splitting of uranium or plutonium, so the fusion part is, in a sense, a cleaner bomb than the other part, so people thought they could Didn't we figure out how to make a fusion bomb without the fishing part? No one has ever figured out how to do it. Well, go ahead, to make nuclear bombs there are basically two key potential materials for the bomb. Next time we'll talk more about how to do it. make these the first, it's highly enriched uranium.

Well, when you extract uranium from the ground, less than 1% is the type that is easy to split, uranium 235, 0.7% is uranium 235 and 99.3% or so is uranium 238, wait, uranium 238 is almost useless for fishing , it will split under certain circumstances, but it can't support a fish and a chain reaction, so you have to separate this, you have to figure out how I can get from 0.7% to very high concentrations of uranium. 235 almost everything and that process is called enrichment the more percentage of u-235 you have in your uranium, the more enriched uranium it will be, so when people say highly enriched they mean 20% or more uranium-235, that is the definition international highly enriched uranium and almost All of the techniques that people have thought about about how I can separate those u-235 atoms from the u-238 atoms have to do with a very slight difference in mass, so the mass basically it is the number of protons and neutrons. in the core then you know 238 instead of 235 so you know just a little over 1% difference in mass and that slight difference is what most approaches play on and we'll talk about a couple of the approaches that have been done next time, but there are gaseous diffusion approaches that use enormous amounts of energy, there are centrifuges, there are a variety of others, okay, plutonium is what they discovered to do with uranium 238 if you put uranium in a reactor and there is a chain reaction that grows insteadexplosively like an atomic bomb, you have a steady state chain reaction, you still have neutrons everywhere, okay, and some of those neutrons when they hit uranium 238 elements are absorbed, so you have uranium 239, but uranium 239 no It's not stable and it ejects some stuff and it decays into plutonium 239, okay, and plutonium 239 turns out to be a good weapons material, just like you're in m23 five, so you can take this, you know, useless uranium 238, convert it into plutonium. -239 once, but you only end up with something like 1% plutonium in the spent fuel of a reactor, so you have to chemically separate the plutonium you want from all the other stuff, the remaining uranium, the fission products that They are intensely radioactive. and unpleasant, you want to get the purified plutonium and that chemical process of separating the plutonium is called reprocessing.

Well, we'll talk more about that next time, there are some other isotopes that have this property that they are large enough and unwieldy enough that when a neutron hits them, they will split up and release more than one neutron, so you can have a chain reaction, but there is no other that has been used for nuclear weapons stored in a state where now the key point is none of These materials are found in nature, there is not a rock that you can turn over that has uranium highly enriched in rock or plutonium in rock. They are all extraordinarily difficult to produce, so in a sense, Mother Nature has been both kind and cruel. for us in the way he established the laws of nuclear physics that these materials do not exist in nature and are difficult to produce, so our species did not invent them until we had developed civilization to a degree level.

Reasonably extensive but cruel in the sense that once you have these materials, it is actually not as difficult to make a nuclear bomb as it would prefer to be now, as I mentioned, the quantities of material required are not very large, so What this hand has is a glass ball, not a plutonium ball, which is the same size as the Nagasaki bomb ball, so it's just not a lot of material for the gun type bomb, you need more , as I mentioned, but the amount that you have, because uranium is a very dense metal, it fits approximately in two 2-liter bottles, and again, as I mentioned, it's only six kilograms for Nagasaki. of order 60 in Hiroshima due to the greater efficiency of the implosion bomb plus it is not particularly difficult to smuggle this material this is a guy called Sergeant She Blair carries in one hand a box containing the plutonium core for the Trinity nuclear test, the first nuclear bomb, you can see that he has no special equipment, he is wearing a noticeably dirty t-shirt and chinos and carries them in one hand so that once the nuclear material leaves the place where it is supposed to be if it is stolen. or something like that could be anywhere and trying to find it and recover it is a very difficult job, it is radioactive, any material that you can make a nuclear bomb with is an atom that is unstable and therefore it is radioactive and you can detect it . radioactivity, but it turns out that highly enriched uranium, especially, and also, to a lesser degree, plutonium, are not so radioactive as to require special equipment to transport them or to make them very easy to detect years ago.

I was talking to a guy who had done sort of an international survey on radiation detection equipment that was available for people to install at borders, etc., and one of the things you'll see at airports and things so they're international, you'll often see the customs officer carrying a little pager on his belt, well that's a radiation detector, so I told this guy who did this study of the equipment, let's say I'm a type of customs. I have one of those things on my belt, the bag directly in front of me, the one I'm looking at, finally has enough left for a bomb, what's the chance of that detector going off?

He said zero. Well, now the larger detectors, that's not true, the larger detectors have some chance of detecting highly enriched uranium, but it's relatively easy to shield some of the radiation that it emits is similar to things that are normal radioactivity. You would be surprised how much radioactivity there is around us in nature. You get a certain dose of radiation when you eat a banana, for example, and cat litter is one of the things that routinely sets off radiation detectors at borders, so detection is another problem, but it's just not that difficult. smuggling new ones, cleaning the toilets, the point I'm trying to make clear, some somewhat misleading terms that you should remember first though. all of the highly enriched uranium I mentioned is 20% or more uranium-235.

Natural uranium is what is extracted from the ground and is 0.7% uranium-235. Low enriched uranium is when it's more than 0.7 percent but less than 20 percent typically for a power reactor, you're talking somewhere in the range of 4 to 5 percent uranium-235. Depleted uranium is what you get when some of that u-235 has been removed to produce highly enriched uranium or to produce low enriched uranium and then the waste you have is almost all UNM 238 is what is called depleted uranium, so which has less than 0.7 percent u-235. This is where things get tricky. Weapons-grade uranium is usually a little different in different countries, but it is usually uranium. certainly, at 90% or more in the United States, that's officially ninety-three percent or more uranium-235, but bombs can be made from material that is much less than the weapons network.

It is an irony of history that the Hiroshima bomb was the first nuclear weapon. used in the war was not made of weapons-grade material, it was made of 80 percent highly enriched uranium, similarly weapons-grade plutonium again is a little different depending on where it is found, but it is generally 93 percent hundred or more plutonium. 239, what isotope do you want? Why is plutonium-239 the isotope you want? It turns out that if the material absorbs one more neutron, it becomes plutonium-240, and plutonium-240 has a huge spontaneous fission rate, breaking apart and releasing neutrons. all the time, so you end up with a lot of neutrons flying around if you have a lot of plutonium 240, which makes it harder to make your nuclear bomb, plutonium 238, which is produced in a slightly more complicated way, but it comes up a little As you were radiating that uranium increasingly generates a large amount of heat.

Plutonium 241 is not as bad as 240 or 238, but still not great, and so on, plutonium 239 is what you prefer if you are a bomb designer. To have it in a power reactor, what you do is leave the rhenium as uranium fuel in the reactor for a long time to produce energy efficiently in a weapons plutonium production reactor, you leave the material for a time relatively short. to maximize plutonium-239 and minimize the degree to which it absorbs more neutrons to accumulate these undesirable isotopes of plutonium, so what you get from a power reactor is called reactor-grade plutonium has much less plutonium-239, perhaps only 60 % or 70% plutonium-239 and weapons manufacturers prefer weapons-grade plutonium, but as with uranium, it is possible to make reliable and effective nuclear weapons from reactor-grade plutonium once the plutonium has been separated of spent fuel through this known process. as reprocessing, so this goes more to the point that you can make bombs with reactor plutonium, it has a higher neutron emission rate, it has a higher heat emission, i.e. higher radiation, all of this can be addressed by the bond designers and this is just a long disquisition on that topic officially from the US government this again comes back to the point that highly enriched uranium well below weapons grade is usable in weapons this is how much material you need if you have a neutron reflector around a sphere based on what percentage of uranium-235 is and what I want you to see is that the graph is pretty flat for a long time until it gets to sort of 50 60% uranium-235 and that's when it really starts to go up now there as I mentioned that there are other isotopes that could possibly be used in nuclear explosives.

There are none, they are very difficult to produce and separate. Only a couple of countries have kilogram quantities of separate materials from these other isotopes, so I include them just for completeness. Okay, what are the difficult parts of making a nuclear bomb? First, make the nuclear material, which is overwhelmingly the hardest part. More than 90% of the effort on the Manhattan Project went into manufacturing the nuclear material rather than designing, manufacturing, etc. in fact, of the bomb in the Manhattan Project, as I'll talk a little about the next time they built in just a few years an industrial space that was larger than the entire US.

The auto industry that existed at the time used I think something like 5 or 10% of all the electricity generated in the United States to enrich uranium. It was a gigantic industrial undertaking to manufacture nuclear material usable for weapons. Well, the second difficult part is If you want to make the kind of bomb that I would want to have something that is efficient, safe, reliable, predictable, that you can put on a fighter jet or, better yet, a bunch of ballistic missiles, it's a lot. more difficult to manufacture that type of bomb. a bomb than to make a terrorist nuclear bomb which would be crude and unreliable, perhaps placed in the back of a truck, unfortunately that is much easier to do if you have the nuclear material, so the security of the nuclear material is sufficiently important to preserve it.

It's beyond the reach of terrorists to be the topic of these global nuclear security summits that have been going on since 2010. Okay, the third really difficult part is designing and manufacturing a hydrogen bomb, that complex thermonuclear weapon. I talked about thermonuclear hydrogen fusion. that refers to the same thing, which is extremely complex and I think it's very difficult to achieve without some degree of testing, there is no central secret to making nuclear weapons, but there are a variety of very real engineering and manufacturing challenges, so I suppose I am a terrorist group and I have much fewer resources than a state has.

I don't have anything like the money that a state has. I don't have anything close to the organizational capacity that a state has. I don't have anything resembling technical experience. that a state has how am I going to make even a crude nuclear bomb, so the first part is difficult, getting hold of the nuclear material again once they have it, which unfortunately there is a significant risk that they could make a crude nuclear bomb . and that has been the conclusion of repeated studies done by governments not only in the United States but in several countries in other parts of the world, so even once you have the nuclear material, although it is still somewhat difficult, I think it would be the most technically challenging attack ever made. any terrorist group has ever managed, if this were to happen, they have to process the material in a suitable way to be able to obtain, instead of metal, they could obtain, for example, fuel for research reactors which is usually a mixture of aluminum and uranium , and they would actually have to do it chemically.

Separate the uranium from the aluminum and then they would have to convert it into metal, so some degree of chemical processing may be required depending on the type of material they manage to obtain. Now, on the other track, it's possible that Well, tariffs couldn't do that, but then it turns out that there are a lot of things that we know terrorists and other adversaries do routinely that involve a fair amount of chemical processing, from a poppy plant to heroin, actually involves a substantial and quite sophisticated process. chemical processing set, all good, casting and machining, once you have the metal you need to mold it into the right shape for your bomb components, then you need to machine it to make sure it is exactly the right shape, you need to build your explosives. reflector, etc. and to make them work if you wanted to make a standard type implosion weapon then you would have to have explosives with precise shapes and very precise timing etc. it's really quite difficult and all of that requires you to be able to recruit, train trained people, raise money and sustaining an organizational effort over a substantial period of time, which is something that terrorist groups in most cases are not good at, so some scenarios might allow you to skip some of these steps just to give you an idea in In the US Department of Energy there are some facilities where security rules require them to have a security plan that prevents terrorists from even reaching the nuclear material, much less leaving the facility.building with nuclear material because of concerns that terrorists could unleash a nuclear bomb. explode while they are still in the building, if they manage to get there, I won't say more than that on that topic, so here are some technologies that you might want to remember because sometimes they appear in the news, cry, Tron's are devices to deliver a very powerful electrical signal, a large spark with very precise timing and they have civil applications, they are used for example in licit ripsi to break up kidney stones, a subject very dear to my heart as I have had kidney stones several times, but They are used to detonate explosives in implosion systems.

There are several alternative approaches that can also be used to detonate explosives. Neutron generators. This is another of our hearts. One of the difficult parts to get. Do you want a neutron shower to activate? at exactly the right time, but it's a time when the conventional explosion is already crushing the nuclear material, so you have to figure out how to make something that generates the neutrons you want at just the right time and in the right way and that doesn't Unleashing a bunch of neutrons in advance is a bit tricky, it's not necessarily necessary for gun-type bombs because they can rely on stray neutrons that are always present, but it is necessary for implosion-type phones.

X-ray flash photography is another thing that is often used. especially in state programs because you want to be able to take a sort of strobe image of the system imploding to see if it's imploding correctly. All of these things are subject to export controls. They also have civil uses. Well, let's talk for a minute about the effects of nuclear weapons and just to give you an idea, this is what Nagasaki looked like a month after the bomb was dropped, you can see it is a picture of almost total devastation and destruction, so that the first thing that happens is the nuclear fireball, so let's go back. to our ball of nuclear material, so in less than a millionth of a second we have released the equivalent of, say, 15,000 tons of chemical explosives in a ball.

This selection the ball has not yet had a chance to expand, so all the energy is contained in this small space, so we are talking literally billions of degrees, much hotter than the center of the Sun at the center of this ball, okay, and incredible pressures, okay, so that ball is going to radiate like crazy, it's going to send out gamma rays. x-rays, etc. because of that incredible temperature and pressure, and that pressure will cause it to fly outwards, so the ball will grow at an incredible rate sending out these gamma rays, x-rays, etc. and as it gets bigger and at least a little colder, it will still be a fireball, but it will send visible light, infrared light, etc., so this is an image of the fireball from the Trinity nuclear test.

You can see that this was sent on a tower a little above the ground, but the fireball was large enough to come into contact with the ground and actually melted. You can still go and visit the site. It melted the sand and rock underneath and you can go to that. site and collect small pieces of what is called Trinite, which is the type of molten glass that resulted from that friend of mine, in fact he took a piece of Trinite to the laboratory and managed to detect the presence of an isotope created when the barium in the Los explosives absorbed neutrons from the ongoing reaction and decades later, only from a piece of material collected from the ground, was he able to confirm that barium was used in the Trinity test explosives, which is in fact true.

So at the edge of this expanding thing, there's still this incredible pressure on the kind of outer edge as it moves outward, which is called the shock front and it's labeled here and you can see there's kind of a earth cloud while lifting earth. Alright, so this fireball is hot and in the middle it no longer has high pressure, so what happens with very hot air is that it rises, so the fireball is incredibly hot, the explosion dies out like this , the fireball is starting to rise because it's hot and it's starting to spread and it's absorbing the air that goes up into this column, it's okay because it's rising and to avoid creating a vacuum below where it was, the air comes in through the sides and up this column and then out. and creates the classic mushroom cloud, okay, so the question is to what extent the various effects occur and the answer depends on the size of the bomb, as you might expect.

One of the surprising things is that different effects scale differently with the size of the bomb, some of them scale by about 1/3 power, just like the bomb explosion scales by about 1/3 power, some of them scale by 0.4 power, approximately the thermal, the radius at which thermal effects will be enough to establish themselves. burning things or to cause third degree burns or whatever, the scales are about the power of 0.4, but the radiation radius increases by a much smaller number, which means that for small bombs the radiation is more important than for large pumps. For large bombs, other things become more important, as seen here, so the immediate radiation in the case of a 1 kiloton bomb, a small nuclear bomb actually extends further as a potentially lethal effect than any of the other effects, while for a hundred kiloton bomb it is the thermal one that extends further and even the explosion extends beyond the immediate radiation, so I must say that there are actually two types of radiation from a nuclear explosion, one is what's called immediate radiation, so as I mentioned, you have gamma rays, X-rays released essentially. instantly and you have neutrons that are released essentially instantaneously, but you also have the delayed radiation that comes primarily from fission products that are extremely radioactive and what happens especially if there are two ways to detonate a bomb, you can detonate it. in the air, which turns out to be better for creating a large explosion in a wide area or you can detonate it directly on the ground, called a ground explosion, which is better if you want to destroy hardened things right near where the explosion is . an underground missile silo or an underground command bunker or something like that, whether it's on the ground or near the ground, is best for that purpose, but if you're on the ground or near the ground, what happens is that the ball of fire comes into contact with the earth, vaporizes a bunch of rocks and everything that's on the ground there and those things get absorbed by the mushroom cloud, mix with those nasty fission products that are actually products of Radioactive fission while it's in the mushroom cloud and then starts falling downwind from the reaction that's called fallout is fine, so if you have a mid-air explosion to maximize the area over which you're destroying buildings , there is no radioactive fallout there, the fish and products rise to the upper atmosphere and disperse throughout the Earth.

There's no stuff raining downwind of the explosion, but if you have it close enough to the ground for it to come into contact, the fireball comes into contact with rock dust, etc. and absorbs it into the cloud, then you'll have radioactive fallout, okay? this is this here only refers to the immediate radiation, neutrons and gamma rays, etc. so the fireball, there's the explosion, let me talk a little bit about the explosion, the explosion is basically a big wave of shock like you would have with a conventional shock wave. It's just that the bomb is much bigger over a much larger area and with the combination of effects it's generally thought that most people who are in the area if it's a pretty big bomb like, you know, 10 20 30 kilotons and Furthermore, most people who are in the area that has at least 5 pounds per square inch of explosion pressure, called overpressure, will probably die, most people who are outside the 5 PSI radius will probably live Now, that's a very, very, very rough approximation and there are much more detailed models and effects calculators, etc., but there are calculations that have been done over the years that use what's called a cutoff model. cookies in which they simply assume that everyone dies within 5 psi and no one dies outside of 5 psi and the mistake that is made in assuming that everyone dies within 5 psi. 5 psi is similar in size to the error in assuming that everyone survives outside of five psi, but it's an oversimplification, it doesn't really work if the population isn't homogeneous over a wide area on its own, so this just gives you the areas that go along with those effects, so this is a slightly more detailed calculation of who would die, so this is where the overpressure is greater than 12 psi, so almost everyone dies in the 5 to 12 psi range, order the half the time. people die and almost everyone is seriously injured in some way, then you have in the outer ranges some people dying, a considerable number of people are injured as you move towards one or two psi, you have a minority of people who are injured So what kind?

We are talking about injuries, so, first of all, from the explosion, what usually happens is that people are crushed, buildings fall, etc. from the heat, we're talking about people getting burned by the immediate radiation, we're talking about radiation illnesses that could affect you. a couple of weeks to kill you, as if the dose was big enough to kill you, so we're talking about, in the case of Hiroshima and Nagasaki, tens of thousands of people were killed in really horrible ways and tens of thousands more They were really freaking terrible. injured, so what we've talked about today are the basics of nuclear weapons.

Some takeaway points: Highly enriched uranium or plutonium is needed for a nuclear bomb. It is difficult to make the amount of material you need. However, it is small. The most difficult part of making a nuclear bomb. The bomb is manufacturing the nuclear material. However, there are other difficult parts and the effects are overwhelming. A single nuclear bomb can incinerate the heart of a major city, so next time we'll talk about how plutonium and highly enriched uranium are produced. Thanks again for tuning in.