The Biggest Bangs

you today's topic is nuclear weapons and the reason I'm telling you about them is I want to make sure this is distinguished from nuclear power and the real key here is the following uranium comes out of the ground with very little of uranium-235 that's the physical stuff the stuff that can fission easily with any energy Neutron to make a nuclear reactor work you need to enrich that fuel to 3% that will not make an atom bomb to make a bomb you need the uranium-235 to be at 90% and that's why facilities like this one of centrifuges is very important enrichment facilities are large they take a lot of energy and a lot of time to get the uranium up to that type of purity level you could say of the u-235 the reason this is needed is because you need to have enough of the fission reactions go off fast enough before the entire thing to semi rates after all it's a bomb let's look at what's inside them we somehow have to get to this amount of uranium-235 or other fizzle material like plutonium 239 all in one spot critical mass if you have too little of it the neutrons will leak out before they are able to initiate another fission reaction so there's a key amount of the material that's needed a critical amount a critical mass if you just started with that critical mass you would automatically have a bomb it would spontaneously at some point emit a neutron which would then trigger the entire chain reaction and that wouldn't be very useful so you need to decide to assemble the two pieces that are subcritical into a critical mass one way you could see Illustrated here is you've got two halves and you having a regular chemical explosion like you know TNT it pushes them together in another system you start with something spongy in other words not at the full density of the metal and you take explosions from around the side and condense it together it's called an implosion method so the very first bomb use this gun type method and it wasn't really two halves you can see you have this hollow cylinder subcritical and then you have this cylindrical target here also subcritical and you basically like a gun shoot this so that it will come and go over the top of it and you might say yes am I gonna keep going sure but we only need microseconds for this chain reaction to start up and go all the way to completion meaning you have an uncontrolled release of the nuclear energy there are some things you can do to allow yourself to use less of the critical part less a smaller critical mass and that's this other stuff that's sitting around here right this is often called the tamper or a neutron reflector since the key is keeping those neutrons around long enough to cause chain reactions if you have things that will either produce more neutrons or bounce the neutrons back in then you need less of the fuel in the first place there are other parts of bombs you don't want to just rely on that first Neutron having to start up so often there is some type of trigger as well that will start the first neutrons coming out which will then initiate the chain reaction this is a video of the first atomic bomb test the Trinity test in New Mexico was during World War two there was worries that other countries were making nuclear weapons not just the United States and to be able to end World War two we needed to get them before other countries did one of the things you noticed in that video was the mushroom cloud and it's basically hot gases rushing upward because we've made such an enormous amount of heat right here where the bomb exploded the superheated air Javier Rises goes up and at some point in the atmosphere the temperature of the air becomes less because it's cooled and it will now billow out sideways into a cloud the typical mushroom cloud shape that people associate with nuclear weapons one of the keys to understand is that this doesn't have to be a nuclear weapon it just has to be a really really big explosion and you have that you will get this type of phenomenon the hot superheated gases rise up into the atmosphere until they reach a point where they cool they stop rising and since this sucks up so much dust and dirt and debris this cloud doesn't look like your normal white cloud right this cloud will have more gray in it and darkness because of course all this dirt came up should also mention about fallout you see the fission products from a nuclear explosion are not contained and that means you have a lot of different radioactive substances in addition the neutrons that were produced the sudden burst of neutrons and made the chain reaction will also make some of the surrounding dirt and area and things that it hit also into radioactive substances these then come up into this plume and this plume will spread out and that's the fallout the original nuclear weapons were relatively small maybe 25 kilo tons what that measure means is that's 25,000 tons of TNT of dynamite of normal high-energy explosive 25 kilotons is a small bomb by today's standards today these bombs are often in the Megaton range equivalent to a million tons of TNT going off all at once even the power of a mere 25 kiloton bomb is devastating last year I went to the Hiroshima memorial site saw the original pictures of the devastation and it is truly horrifying the destruction this type of weapon can do of course it's pretty horrifying the destruction any types of weapons in war can do the immediate area around where the bomb goes off receive such high heat that everything is incinerated then there's an area around here because of this wind because of this mushroom cloud going up there is an enormous blast wave an enormous shock wave winds like a tornado 300 miles an hour trying to knock everything down and from this the gamma rays that come out right the the initial radiation at Oshima was a slightly larger area where people would get radiation burns from this even if they were not incinerated or blown away today's bombs the much much larger ones have a little different confluence of zones their radiation zone of course may be a bit bigger but the blast zone and the air zone where you hit the 300 mile an hour winds are even larger so while it's kind of silly to say this if you actually survive seeing a nuclear bomb go off you don't have to worry about the radiation you have to worry about the fallout but this area where the invisible gamma rays may have penetrated your body is far inside the place where you would have been incinerated to dust and blown away so the bear gun type bomb using uranium-235 was the simplest design and the one they haven't had the most confidence would really work that took a lot of the fissile material and that's the real difficult thing in making a nuclear weapon the designs everything I'm showing you it's on the web right and Wikipedia or some other easily searchable website the key is getting the fissile material look at this comparison if you're using uranium-235 and you just want to not use something that reflects the neutrons which takes a lot more Engineering you can see you need a lot more of the fuel of the weapons-grade material if on the other hand you use a tamper something that would reflect the neutrons your critical mass knee drops dramatically and then there's plutonium 239 plutonium does not naturally occur it has a half-life on the order of 24,000 years so even if some was made in the Big Bang it's long since gone you can make plutonium though in a nuclear reactor now the thing is that if you try to make this in your run-of-the-mill power generating nuclear reactor you get the wrong mix of isotopes the plutonium that comes out of your fission power plant down the street making electricity is not plutonium 239 it once again is a mix of isotopes you'd have to go to your centrifuges or other enrichment facility and pull out the plutonium 239 of course if you could do that you could not even need to make plutonium in the first place you could just start with uranium you can simply find or mine or buy but if you design a reactor just right military reactor it can actually turn uranium into plutonium and you can take that plutonium out and extract it and it does have the right isotope mix it is the plutonium 239 and you can see the plutonium-239 is much more efficient you can use less of it to be able to make the same size bomb and once again if you then add some type of neutron reflecting material you're able to do it even with a smaller amount of the critical mass of substance the next bombs are made we're using the implosion type and this takes a lot more engineering because even though you have this plutonium core and a neutron initiator to give you the bang right where you want it you have the tamper material and then you have this high explosive around here that you need to push together and have it work just right and have it condense this material without blowing it through one side or another much trickier engineering here's an animation that sort of shows what needs to go on the high explosives go out they crush the tamper push the tamper down to the plutonium the trigger goes off and now you get the initiated critical mass nuclear explosion the US was the first one to create test and illustrate fission nuclear weapons wasn't too long after that that the Soviet Union did it and then after the Soviet Union the American European allies of the United Kingdom and France and then China for a long time it were those five countries that had nuclear weapon capabilities in fact those are the five permanent members of the UN Security Council for exactly that reason in time of course the genies out of the bottle the science is known and if a country is dedicated to doing their enrichment they can make nuclear weapons as well in the 70s we saw India join this club and then Pakistan now it's rumored that both Israel and South Africa also had the capability not proven but probably likely in fact I would say any advanced technologically advanced country could make a nuclear weapon if they wanted to and that's the real key because many have signed treaties that say you know there's enough nuclear weapons around we don't need to make them ourselves we can rely on our allies or now that the Cold War is over maybe we don't even need them at all the most recent member of the nuclear Club is North Korea North Korea has demonstrated several nuclear devices over the last few years if you think a fission bomb is big then what about an h-bomb an h-bomb is a hydrogen bomb because it actually uses nuclear fusion that's the energy source the Sun has but it isn't easy to do at all you see we first need to start with your same atom bomb I just showed you this is an implosion type nuclear weapon and we need that to get the temperatures high enough to actually get the deuterium and tritium to combine and fuse the only way to get this high enough temperature and high enough density is put it inside an atom bomb and blow up the atom bomb a tritium has a short half-life of 12 years so the clever way it's done is you actually create the tritium in place and that's why there's this lithium-6 deuteride deuterium and tritium is what will fuse but if you put enough neutrons into lithium it turns into tritium so how do we get those neutrons when we need to multiply our neutrons so you can see that you have uranium here as a tamper which will create more neutrons and you even have a plutonium spark plug that once there chain reaction takes place and we've created this tritium we're going to have an even bigger regular fission explosion which can then trigger the fusion explosion H bombs were invented through the 50s and in 1956 the u.s. tested one here's the sequence that it goes through we have it sitting here we have the nuclear bomb go off you have reflecting materials making neutrons come in these neutrons multiply it creates the deuterium tritium fuel and finally that deuterium tritium ignites and you not just have maybe your one Megaton bomb or half a Megaton bomb but now you have something in the ten of megatons this video is at Bikini Atoll in May 1956 and this is where the US tested the first h-bomb we've got two different views of it and you can see that the blast is incredibly large they expected this bomb to maybe be three megatons but it turned out to be fifteen the age of yet bigger and bigger bombs was born it wasn't too many years after this that the Soviet Union also created their h-bomb in fact they made the biggest bomb that's ever been seen in the world while the Tsar Bomba over 50 megatons of explosion it's really wonderful that nuclear bombs have only ever been used in one short time period in the world my sincere hope and I'm sure everyone's in the world is that they won't be used as weapons what I wanted to illustrate today is that nuclear weapons are very different things than nuclear power controlled fission chain reaction can be extremely beneficial to mankind a uncontrolled fission reaction or fusion reaction um this of course not all that great for mankind that's what you need to know about nuclear weapons you [Music]

Channel: Illinois EnergyProf

Views: 83,058

Rating: 4.9453459 out of 5

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Id: fRsfbDpBE-s

Length: 18min 23sec (1103 seconds)

Published: Tue May 14 2019