vas-y, viens, on construit une bombe atomique — Transcript

Full transcript

1. 0:00Uh. .
2. 0:00. Why?
3. 0:01What do you mean, why? Have you ever watched an atomic test and wondered, how is that possible?
4. 0:05Well, I have. And there's only one way to find out.
5. 0:08We're going to build a nuclear bomb from scratch.
6. 0:10As you probably know, we're going to have to get uranium.
7. 0:13But why? Yeah, now that's a good question!
8. 0:16Why! ?
9. 0:18What’s so special about it?
10. 0:19Because getting it, that little bastard, is a pain!
11. 0:22You can find it in pechblende, a radioactive ore that used to be mined in France, especially in the
12. 0:26Limousin. You can probably still find some in an old mine.
13. 0:29But hey, hey, hey, don't go too fast with your pickaxe and knife, because pitchblende has about 50
14. 0:35to 80% uranium. Let's say 65%.
15. 0:37And in that 65% of uranium, only about 0.
16. 0:407% can make the bomb we're building today, because we're not taking the plutonium route,
17. 0:45in this video.
18. 0:46And this ultra-rare uranium, uranium 235, we need 64 kilograms of it to recreate the bomb that
19. 0:52devastated Hiroshima.
20. 0:54Which means that, assuming we're blessed by the gods and lose zero during the enrichment we’ll come
21. 1:00back to, there are 4.
22. 1:0255 grams of uranium 235 in one kilogram of pechblende.
23. 1:05So that means you'll have to mine about fourteen tons of ore, all told.
24. 1:09I hope you've got plenty of vacation days, buddy.
25. 1:12Okay, I'll buy it if I have to.
26. 1:14That's a good idea. It comes in the form of yellow cake.
27. 1:16No, no, no, you don't eat it.
28. 1:18Long story short, you take your pitchblende, process it, and you end up with this uranium
29. 1:23concentrate, at least 80 percent pure.
30. 1:24So, in the best case, we'd need about 11.
31. 1:275 tons of yellow cake.
32. 1:29It sells for around 180 euros a kilo, so that's 2 million euros just for the raw material.
33. 1:35So what makes this element so special that it can justify all that effort?
34. 1:40If it looked like bismuth, I'd understand it, but this.
35. 1:43. .
36. 1:45Go on, make your case.
37. 1:46We're listening, because we want to understand why we need it in the first place.
38. 1:50Let's go back to what we're trying to create right here, after all: a huge explosion.
39. 1:54For something to blow up, we need to create a huge amount of energy inside a limited volume.
40. 1:57That energy turns all the material present into a hot,
41. 2:00compressed gas, so you end up with gas that's under enormous pressure in a very small space.
42. 2:06So this gas wants to expand, to spread out and fill a proper space, and in doing so, it’ll hit and
43. 2:12carry along all the molecules in its path with incredible force.
44. 2:15That’s the shockwave.
45. 2:17And if you’re in its way, the same thing happens to you as to the air molecule.
46. 2:21All at once, you're hit with enormous pressure, which usually kills you.
47. 2:25And if that still isn't enough, since a lot of air molecules have already fled, the pressure is very
48. 2:30low right now. A vacuum starts to form, and the air wants to rush back in to fill that space.
49. 2:35That's the negative blast, there to finish you off.
50. 2:38Nature did a pretty good job after all!
51. 2:40So, to get that famous energy quickly, the most common way is to use chemistry.
52. 2:44And I’m not going to lie to you, I was pretty rusty on chemistry.
53. 2:48I haven’t done any since prep school, ten years ago.
54. 2:50Which lets me answer a question I get asked a lot: How do you know all that?
55. 2:55Well, I don’t know.
56. 2:56I learn by reading papers, books, websites.
57. 2:59Unlike in prep class, I don’t have a teacher to answer my questions anymore, no one left to clear up
58. 3:04that doubt on one point that would make everything click.
59. 3:07That’s where AI comes in.
60. 3:08I love using it as a tutor.
61. 3:10But sometimes, it goes off the rails or gives an unsatisfying answer.
62. 3:13But a quick, effective way to deal with that is to ask another model the same question and compare.
63. 3:19And as you can see on my interface, I did it in one click!
64. 3:22It's a real time-saver!
65. 3:23And that’s because I use Mammouth AI, the sponsor of the video.
66. 3:27A French platform that, for €10 a month—less than any other individual AI subscription—gives you
67. 3:33access to all the latest AI models: ChatGPT, Claude, Grok, Mistral, Gemini, Perplexity, all of them!
68. 3:39You can switch from one to the other in one click, which is great for testing.
69. 3:42And just because it’s cheaper doesn’t mean you get fewer features.
70. 3:46You get image generation, Perplexity’s advanced search, and even ChatGPT’s voice dictation mode.
71. 3:51All while staying GDPR-compliant.
72. 3:52The data’s stored in Germany, and they use a zero-retention policy, so providers don’t keep your
73. 3:57prompts. If you’re interested, I’ll leave a link in the description.
74. 4:01Right, where were we?
75. 4:02Oh yeah—how to use chemistry to blow stuff up!
76. 4:04For example, with TNT, we’re going to make this solid molecule nobody wants to be in.
77. 4:09Nitrogen wants out to become gas, and oxygen would rather bond either to carbon or hydrogen.
78. 4:15But the chemical bonds keep them from forming those gases.
79. 4:18The idea is to create a shockwave with enough energy to break the bonds in a tiny part of the TNT.
80. 4:24The molecules rearrange to form gas and, in doing so, release energy.
81. 4:29Energy that’s enough to break the bonds of its neighbors.
82. 4:32And so on. A chain reaction that turns our TNT mainly into gas.
83. 4:36Gas that normally takes up a lot more space than it does when it’s in solid form, so suddenly you
84. 4:41end up with a huge amount of hot gas trapped in a volume that’s far too small to hold it.
85. 4:45. .
86. 4:47And we know the rest.
87. 4:48Okay, that’s enough to blow up a car.
88. 4:50That’s cute, but we want to blow up a lot more than that!
89. 4:53The equivalent of sixteen kilotons of TNT, for Hiroshima.
90. 4:57And it’s not chemistry that’s going to let us do that, it’s physics.
91. 5:00We’re going to use nuclear energy.
92. 5:02And in the case of a fusion bomb, which we'll briefly touch on, it's quite literally the energy of
93. 5:07the stars themselves.
94. 5:09I don't think we can do any better than that, either.
95. 5:11People have no real idea how much energy is contained in matter itself.
96. 5:15Yet they all know the formula that describes it: E = mc squared.
97. 5:19Energy equals mass multiplied by a constant, the speed of light squared.
98. 5:23And the speed of light is absolutely gigantic!
99. 5:26So even if you take something tiny, like a paper clip weighing one gram, inside it, there are 90
100. 5:32terajoules of energy.
101. 5:33That is equivalent to 21,5 kilotons of TNT.
102. 5:36. .
103. 5:38in just one gram of matter!
104. 5:39The only catch is that it’s almost impossible for us to use all that energy.
105. 5:43. .
106. 5:45Almost. So where does this energy come from, and how can we try to release some of it?
107. 5:51Matter is made of atoms.
108. 5:52Here we have a hydrogen atom: a proton, positively charged, and an electron, negatively charged,
109. 5:57orbiting around it. If I wanted helium, I'd need to add a proton to our nucleus.
110. 6:01But a positive proton next to another positive proton won't stick together.
111. 6:06No, it repels because of the electromagnetic force.
112. 6:10It's like bringing together the positive sides of two magnets.
113. 6:14You won't be able to get them to join.
114. 6:16But it works! Helium exists, and there are two protons in its nucleus.
115. 6:19To fix this, we have to add a neutron.
116. 6:21A neutron has no charge;
117. 6:23it's neutral. That's where the name comes from.
118. 6:25Since it's neutral, it can come very close to a proton without being repelled by electromagnetic
119. 6:31forces, and when they're less than 10 to the power of -15 meters apart,
120. 6:36the quarks in the neutron and in the proton can bind through the strong interaction.
121. 6:41The strong force is what lets quarks, these elementary particles, bind and form other particles,
122. 6:46like protons or neutrons.
123. 6:48This link is created by constantly exchanging gluons between them.
124. 6:52That’s what creates the strong force, which gets its name because it’s the strongest of the
125. 6:57fundamental interactions.
126. 6:59It’s 100 times stronger than the electromagnetic force, which makes two protons repel each other.
127. 7:04The problem is, it only works over a very short distance.
128. 7:0710 to the power of -15 meters.
129. 7:09That’s why our two protons can’t use it to bind together at all.
130. 7:12The electromagnetic force has a much greater range and acts to separate them before their quarks can
131. 7:18ever exert that force.
132. 7:19But the neutron, now that it’s so close, can still manage to get that bond and this strong
133. 7:24interaction after all. It can stick to protons.
134. 7:26And this strong force, since it’s much stronger than the electromagnetic force, completely cancels
135. 7:32it out and makes a stable nucleus with two protons possible.
136. 7:35A neutron is a bit like the superglue of the universe, holding it all in place.
137. 7:39So we’ve just discovered where a good part of the energy stored in matter really comes from: the
138. 7:44electromagnetic force and the strong interaction, both of which are involved in the creation of an
139. 7:49atom. How could we release these energies and then use them to make the whole thing blow up?
140. 7:55If we take our helium nucleus as it is, with just one neutron, it works, it exists, but it’s very
141. 8:00rare. The most common helium has two protons and two neutrons.
142. 8:04That’s what we call isotopes.
143. 8:06Same number of protons.
144. 8:07Different number of neutrons.
145. 8:08So why does one exist more than the other if both work?
146. 8:11Like building a wall with bricks, the protons, and cement, the neutrons.
147. 8:15One neutron works, but you only have just enough cement to keep it in place.
148. 8:20One gust of wind and it falls apart.
149. 8:22Same if I put in too much cement,
150. 8:24Too many neutrons also cause a problem.
151. 8:26I have so much cement it spills over and comes loose from my wall.
152. 8:30You need to find the right balance.
153. 8:32For helium, that's two neutrons.
154. 8:34Just enough cement.
155. 8:35What we just illustrated is the concept of the valley of stability.
156. 8:38Nature is always trying to reach this plateau, this arrangement that lets the atom reach
157. 8:44equilibrium. That's what we'll exploit.
158. 8:47Because by rearranging to reach a stable state, the atom can release some of the energy from the
159. 8:53strong interaction and the electromagnetic force.
160. 8:55The problem is, it’s hard to do that with helium.
161. 8:58With our single neutron, it’s still too stable to disturb.
162. 9:01But something very interesting happens when we start increasing the number of protons we want to
163. 9:06bind together. Helium has two protons and two neutrons when it’s in its most stable form.
164. 9:11If I add a proton, I get lithium, and you might think that it would take three neutrons in order to
165. 9:16make it as stable as possible.
166. 9:18Well no, this time it takes four.
167. 9:20Why, then? Because the electromagnetic force, which tries to pull two protons apart,
168. 9:25is indeed weaker than the strong force, which binds neutrons and protons,
169. 9:29but this force has a much greater range than the strong force,
170. 9:32which can only glue the bricks together if they touch.
171. 9:34So this proton acts on the other and tries to shove it away, even though they’re far apart.
172. 9:40And there’s no glue between the two to really counter that.
173. 9:44So you have to add more.
174. 9:45And the more protons you add, the higher the neutron count has to be compared with the protons.
175. 9:51At some point, it won’t work anymore.
176. 9:53With so many protons, the electromagnetic force on them leaves our neutrons struggling to hold it
177. 9:58together.
178. 9:59So the heaviest elements are the most unstable, which means they’re the easiest to disturb and force
179. 10:04into releasing the energy locked inside them.
180. 10:07We need one that’s abundant here on Earth, so we can extract it easily and put it to use in practice
181. 10:12for us. And uranium is the one that wins out.
182. 10:15There’s a lot of it on Earth, that’s why we use it.
183. 10:18It comes in different isotopes.
184. 10:20Uranium 238 is its most stable form, so it’s not really that interesting to us.
185. 10:25On the other hand, uranium 235, this isotope that’s missing three neutrons, is perfect.
186. 10:30We find it naturally in nature.
187. 10:32If you take a block of uranium, about 0,7 percent is uranium 235, which is where the numbers at the
188. 10:38start of the video come from.
189. 10:39And above all, it's super unstable.
190. 10:42The neutrons can barely hold the nucleus together.
191. 10:45The energy needed to break the bonds between neutrons and protons is extremely small.
192. 10:49So small that one neutron is enough to blow it apart.
193. 10:53When that neutron gets absorbed by the nucleus, it releases a bit of energy.
194. 10:58A bit, but bigger than the binding energy, so enough to tickle our neutrons under the arms and make
195. 11:04them let go. The uranium atom splits in two.
196. 11:07That's nuclear fission.
197. 11:08Two new atoms form, and 2 to 3 neutrons are ejected.
198. 11:11If we take the mass of each of these new atoms, add it all up, and compare it to the mass of the
199. 11:17uranium 235 atom we started with at the beginning, then we'd see that some of that mass has
200. 11:23disappeared. So where did it go?
201. 11:25Well, E = mc2.
202. 11:26It turned into pure energy.
203. 11:28We did it; that's what we were talking about.
204. 11:31We released some of the energy stored in matter, about 200 mega-electron volts.
205. 11:37That's ridiculously little.
206. 11:39But it's just one atom, and for an atom, that's huge!
207. 11:42If we can fission even one gram of uranium 235, we'd get the power of 20 tons of TNT.
208. 11:47One gram! So we have to keep this fission going.
209. 11:51Fission more atoms, as many as possible!
210. 11:53And fission hands us the means to do it on a silver platter.
211. 11:57In fission, as we've seen, 2 to 3 neutrons are ejected.
212. 12:00It only takes two of the three neutrons to hit another uranium atom to create two new fissions.
213. 12:06You can get as many as six new neutrons, which can in turn be absorbed by other atoms, and so on.
214. 12:11It’s exponential.
215. 12:12This is a chain reaction that will allow us to reach the energy required to create a massive
216. 12:17explosion. But there's a problem.
217. 12:19There's no guarantee at all that our neutrons will strike another atom.
218. 12:23They could easily escape from there without interacting with anything at all.
219. 12:27We have to stack the odds in our favor.
220. 12:28The simplest, dumbest option, the one we'll use because I'm dumb, is simply to add some mass to it.
221. 12:34The more uranium atoms you have, the greater the chance one will be in the neutrons’ path.
222. 12:40The mass needed to make sure at least one of the three neutrons causes a new fission is called
223. 12:45critical mass. For uranium 235, it’s 48 kilograms.
224. 12:48But that's assuming we have 48 kilograms of pure uranium 235, which is complicated.
225. 12:52For Hiroshima, the bomb had a little over 64 kilograms, for example, and it was about 80 percent
226. 12:57pure. Well, there are ways to bring that number down.
227. 13:00For example, adding reflectors to redirect the neutrons to the center, or increasing the mass
228. 13:05density.
229. 13:06That’s what was done in Nagasaki, for example, via implosion during the detonation of the Fat Man
230. 13:11bomb. Well, the theory’s done.
231. 13:14It’s time to build.
232. 13:15Yellow cake is our raw material: a powder containing at least 80 percent uranium, of which 0.
233. 13:217 percent is uranium 235.
234. 13:23But we want a material made of at least 80 percent uranium 235 for it to work.
235. 13:28From 0. 7 percent, we have to get to 80 percent.
236. 13:32This is the stage where uranium is enriched, and it’s an extremely complicated and costly process.
237. 13:38Yellow cake, which is, in fact, sodium diuranate, is first converted into uranium hexafluoride gas.
238. 13:44To do this, we dissolve it in nitric acid, oxidize it, then reduce it before we react it with
239. 13:50hydrogen fluoride in order to make uranium tetrafluoride, and then we add even more fluorine gas.
240. 13:56And why did we have to go through all that trouble, exactly?
241. 13:59Well, uranium hexafluoride is just a uranium atom surrounded by fluorine.
242. 14:03And fluorine is great: it only has one isotope.
243. 14:06So all six fluorine atoms are identical, same protons, same neutrons.
244. 14:11By contrast, the uranium in the center can be isotope 238, which we want to kick out, or 235, which
245. 14:18we want to keep. And at low doses, it can be 234.
246. 14:22Perfect for sorting.
247. 14:23The only thing that varies is the uranium atom, and the difference we can use is the three fewer
248. 14:30neutrons in uranium 235.
249. 14:32Fewer neutrons means a lighter mass for uranium 235.
250. 14:36I don't know if you've ever played around with spinning things fast, but if you have, you'll notice
251. 14:42that the heaviest ones end up closer to the edges.
252. 14:45Well, it's the same with our gas.
253. 14:46If we spin it, uranium 238 will be near the edge and 235 near the center.
254. 14:50We use centrifugal force, and we build the famous centrifuges to enrich our uranium.
255. 14:55But watch out! The mass difference is tiny.
256. 14:58We're talking about three neutrons, that's nothing.
257. 15:01So we need a centrifuge that can spin this gas at enormous speed, more than 330 meters per second,
258. 15:07sometimes even 600. Even at that speed, it's not efficient at all.
259. 15:11A centrifuge's separation factor is 1.
260. 15:1410, sometimes less.
261. 15:15So if you take the gas from the middle of the centrifuge, it goes from a concentration of 0.
262. 15:227 percent uranium 235 to 0.
263. 15:237 x 1. 10, or 0.
264. 15:2577 percent. Remember, we need to reach at least 80 percent concentration.
265. 15:30So we have to do this step thousands of times!
266. 15:32You need thousands of centrifuges set up in cascade.
267. 15:35In the first, you put the gas we just got from the Yellow Cake.
268. 15:38You take what’s in the middle, and inject it into the second centrifuge.
269. 15:42Again, you take the result and inject it into the next one.
270. 15:45But you also take the rest, which still contains uranium 235, and you feed it back into the
271. 15:49centrifuge just above to filter it again, because we don’t want to lose anything.
272. 15:54It cost too much!
273. 15:55The further down the cascade you go, the more concentrated the uranium gets, and by the end, we get
274. 15:59to 80 percent. I think nowadays, we even aim for 95 percent.
275. 16:02Then it’s simple: this UF6 gas, ultra-concentrated in uranium 235, you dump it in a sealed crucible
276. 16:09and heat it with magnesium.
277. 16:10The reaction makes liquid products.
278. 16:13Uranium is ultra-dense, so it sinks to the bottom and we can recover it as a bar of uranium 235
279. 16:19enriched to over 80 percent.
280. 16:21Okay, let's talk price.
281. 16:22EDF is gonna love us!
282. 16:24To produce 64 kilos of uranium enriched to 80 percent, we'll need over a million kilowatt hours,
283. 16:30costing around 200 000 €
284. 16:31And that’s not even counting the cost of building all our centrifuges.
285. 16:34And on top of that, it takes a lot of time!
286. 16:36The process takes years!
287. 16:37That’s why there have been few videos on the channel.
288. 16:40. .
289. 16:42I was busy. But I do post a lot on the secondary channel, so subscribe there!
290. 16:45Now that we have 64 kilograms available, we need to make sure it blows up when we want it to.
291. 16:50For that, we’re going to use the original Little Boy design, the bomb dropped on Hiroshima.
292. 16:56We’re going to split our uranium into two subcritical masses, one of 38,5 kilograms, the other 25,6.
293. 17:01And not just any way. The goal is for the two to fit together perfectly.
294. 17:05The 25. 6-kilo mass is the target.
295. 17:08It won't move. We're going to surround it with 310 kilos of tungsten carbide.
296. 17:13Tungsten acts as a reflector.
297. 17:15When a neutron hits it, there's a good chance it isn't absorbed, but reflected instead.
298. 17:20Around the target, we place what are called polonium-beryllium initiators.
299. 17:24They're what will provide the first neutrons that start the chain reaction we saw earlier.
300. 17:29The idea is simple.
301. 17:30Polonium is a very active alpha-particle emitter.
302. 17:33Beryllium, for its part, has the property of releasing a neutron when it is struck by an alpha
303. 17:38particle.
304. 17:39They’re separated by a thin gold plate, which for now blocks the polonium’s alpha particles and
305. 17:44prevents the beryllium from emitting neutrons.
306. 17:46To make it go boom, we need the missing 38.
307. 17:495 kilos of uranium for supercritical mass, and remove that thin gold sheet to produce neutrons and
308. 17:55set it off. We can do both at once.
309. 17:57We're going to propel the other mass at a speed of 300 meters per second toward our target,
310. 18:02using a mechanism similar to the sort found in an actual rifle barrel,
311. 18:06using cordite, an explosive powder.
312. 18:08When the uranium mass slams into the other one, it strips the thin gold layer off the
313. 18:13polonium-beryllium initiators, letting neutrons be released and setting everything off.
314. 18:19Except we’d really rather not be there when it blows!
315. 18:22To do that, when we put this huge bomb in a plane, we connect its timer to arming wires.
316. 18:27As soon as we drop the bomb from our plane, the wires are ripped out and the countdown starts.
317. 18:33Fifteen seconds.
318. 18:35Once the time’s up, the clock closes an electrical circuit, and that lets the other sensors take
319. 18:39over. First comes a barometric switch.
320. 18:42It measures atmospheric pressure, and as soon as that pressure is high enough to show we’re getting
321. 18:47close to the ground, it then hands control over to the bomb’s radar from there right away.
322. 18:51These then start transmitting to measure the distance to the ground.
323. 18:55When we hit 600 meters, the cordite bags ignite, the uranium projectile is propelled, strikes the
324. 19:00target, and breaks through the gold coating.
325. 19:03Neutrons are emitted.
326. 19:04A first fission takes place, then the chain reaction we saw earlier gets underway, and the energy
327. 19:10produced rises exponentially at a frantic rate.
328. 19:13It’s a real race against time.
329. 19:15How many atoms can fission before the energy produced has vaporized absolutely all the materials
330. 19:22that made up our bomb?
331. 19:23The answer is 880 grams of uranium.
332. 19:25Out of Little Boy’s 64 kilograms of uranium, only 880 grams have time to fission and take part in
333. 19:32this blast. The rest is vaporized in the nanoseconds that follow the chain reaction.
334. 19:38The energy produced is so great that the temperature shoots up to several tens of millions of
335. 19:44degrees. It’s hotter here than it is even inside the sun.
336. 19:47The pressure reaches millions of atmospheres.
337. 19:50Everything within 200 meters of the bomb is completely vaporized, and X-rays are emitted in large
338. 19:56quantities.
339. 19:57These are absorbed by the surrounding air, which also starts heating up and forming a blazing
340. 20:01fireball that will cause fires for miles around.
341. 20:04The shock wave we talked about at the very start of the video takes over.
342. 20:08It moves so fast and compresses the air so violently that it makes it white-hot.
343. 20:12A wind of several hundred kilometers an hour sweeps everything in its path.
344. 20:17All buildings within almost two kilometers are certain to be leveled, and third-degree burns are
345. 20:22guaranteed. The shock wave will stop almost five kilometers from the initial impact.
346. 20:27Moreover, if we look back at it, we’d see that the fireball,
347. 20:31now less dense than the surrounding air, would have risen at 440 kilometers per hour,
348. 20:35creating a suction that pulls dust and debris off the ground,
349. 20:38thereby forming the famous mushroom cloud of an atomic bomb.
350. 20:42The debris also mixes with the fission products, and as a result it becomes radioactive.
351. 20:46Then the wind carries them away for thousands of kilometers.
352. 20:50That is what we call fallout.
353. 20:51The rumor says that if you want to be sure you're safe in an atomic blast, you should form a thumb
354. 20:56with your hand and use it to point at the mushroom cloud.
355. 20:58If the mushroom cloud is bigger than your thumb, then I've got bad news for you, I'm afraid.
356. 21:03Some even say this test inspired Fallout's famous mascot.
357. 21:06But I have to admit that I am not sure it really works for the bombs used today.
358. 21:11The newer ones add nuclear fusion to the mix, and that takes us to another level.
359. 21:16Theoretically, it can yield over 100 megatons, compared with Hiroshima's fifteen kilotons.
360. 21:21At that point, everything within almost seven kilometers of the impact is vaporized.
361. 21:27Everything within a 70-kilometer radius will suffer third-degree burns.
362. 21:31For 32 kilometers, Most buildings are completely flattened.
363. 21:34Drop that on Paris, and you'd have around 7 million dead and 4 million injured.
364. 21:39May we never see a scenario where this weapon is used again.
365. 21:42I hope you enjoyed this video.
366. 21:44I wanted to try something a little different.
367. 21:46I want to stop limiting myself to IT, and only IT.
368. 21:49Tell me if you liked it or not.
369. 21:50I'm moving into engineering more broadly.
370. 21:53It's not the end of computing.
371. 21:55I still have a couple things to cover, but I want to branch out.
372. 21:58V2F, subscribe, comment, like.
373. 22:00Bye bye!