Actually it over simplifies how they work. Especially the plutonium portion... it isn't quite as easy to make it because bombarding uranium with neutrons doesn't just make plutonium 239, it can also create plutonium 240 and plutonium 238, both of which don't well for making a bomb. Even the implosion bit is off because the shaped charges can't be made of a homogeneous explosive because you need to focus the explosives with slower explosives so the force pressing the ball is better equalized... otherwise you risk the explosive charges shredding the ball instead of compressing it... This is a good elementary school explanation but that's about it.
To clarify: a critical mass is when each fission causes one additional fission so the fission reactions stay at a stable rate (what happens inside a nuclear reactor), a subcritical mass produces less than one additional fission per fission event thus the reaction dying off, and a supercritical mass has more than one additional fission per fission event, so the reaction rate keeps growing. Nuclear bombs, when they detonate, create a highly supercritical mass so that the reaction rate accelerates extremely rapidly and fissions a large fraction of the uranium or plutonium present.
8:30 Another clarification: Most plutonium 239 is created in nuclear reactors, where there are lots of neutrons flying around. Some of the Pu-239 formed will absorb an additional neutron forming Pu-240. This isotope of plutonium has a very high spontaneous fission rate, which means there are always extra neutrons flying around inside a chunk of Pu-239. As a result, you have to bring the subcritical pieces of a bomb core together very fast into supercritical mass before those neutrons can get the chain reaction going and blow things apart. This turns out to be much faster than a gun-type design can produce, so they had to switch to implosion. As a bonus, implosion creates a much denser supercritical mass and thus allows much more of the plutonium present to fission. IIRC, Pu-239 also has a higher spontaneous fission rate than U-235, which didn't help. This made the gun-type plutonium bomb design almost impractically long to begin with, then they discovered the problem with Pu-240's fission rate, which made it impossible to make a gun-type bomb of any reasonable size. You can find pics online of prototype "Thin Man" plutonium bomb casings that they made before the spontaneous fission problem nixed the whole design. They're roughly twice as long as the Little Boy uranium bomb, and that still wasn't long enough to work.
Conventional PWR reactors run on about 5% enriched uranium. 20% enrichment is considered "high assay low enriched uranium" and is used in smaller naval reactors.
Not sure, but subs may use even more highly enriched uranium to keep the reactor small and easier to fit inside the pressure hull. Also, reactors for the newest subs are designed to last the life of the sub, so need more fissile uranium to start with in order to last the 40 or so years they expect the sub to be in service.
Just the explosive lens itself is an insane feat of engineering. Using geometry, and chemicals with different combustion speeds to turn outwardly expanding explosions into an inwardly collapsing implosion. Even mechanics of the neutron source at the center of the imploding core is also fascinating, and genius. For better or for worse, the people who worked on the original Manhattan Project were very very smart, to say the least.
When it comes to enrichment, an important thing to keep in mind is that the difficulty lies in getting STARTED with enrichment. Once you get to 4-5% enrichment, you're basically 80% of the way there. You need massive numbers of centrifuges (if that's how you're enriching it) to get very low-enriched uranium. Once you have that, a very small number is all you need to keep going, using only as much power as a grocery store. While 4-5% is useful for a reactor, it's VERY difficult to locate and identify a facility converting LEU to HEU. You don't need massive power feeds or tons of floor space. A few dozen easily-concealed centrifuges is all you need. Additional fact: the reason UF6 is used (other than being the only uranium compound that's gaseous as semi-reasonable temperatures and pressures) is the F is a compound that, by and large, only has one isotope found in nature and as such is one less mass difference to deal with.
Ok, but where does the first neutron come from that starts the chain reaction. Is there something like spontaneous nuclear fission in uranium/plutonium that releases neutrons ?
The radioactive material contains neutrons. They’re always colliding in the nucleus. It’s compressed so that it’s a chain reaction instead of normal decay.
This is an interesting description of the Teller-Ulam design for a thermonuclear bomb. At least public information indicates that this is a likely possibility for the thermonuclear bomb. Us human beings are really great at making tremendously destructive devices.
The Born-Oppenheimer approximation is central to understand how Nuclear Bombs Work. BO says nuclei move at least 1/2000 times the speed of electrons. Hence nuclear fusion begins when the electron temperature is high enough to activate D-D or D-T fusion.
Latter the explosive lens was simplified in a tubular explosive charge, using a solid oblate spheroid Plutonium pit, and thus achieving the same symmetric compression, but this arrange allow make smaller - in size; bombs, and so put 10 thermonuclear warheads in one ICBM.
A symmetrical explosion was an extremely difficult question at Los Alamos. The basic problem is similar to squeezing an orange with your hand: juice squirts out in lots of places because the inward-moving compression is not symmetrical. The solution was to use two different explosive types, with different rates of burning. They are carefully shaped to create the "perfectly symmetrical explosion". (The details need a diagram which you can find elsewhere on RUclips". ) The difficulty resulted in testing the plutonium bomb at Alamogordo in July 1945, with the shaped charges, before dropping one on Nagasaki. The uranium bomb shot a uranium "bullet" into a uranium target. That was a much simpler design, and the Hiroshima bomb was of that type and was not tested before being used on Hiroshima.
Good question! The CANDU reactor uses unrefined uranium which still contains some U-235. It is this U-235 which is still central to its production of energy.
@@RealChemistryVideos The trick to make CANDU reactors work , and they use natural Uranium ( 0,7 U 235 and 99,3 U 238 ) is That U can not use normal Light water ( H2O ) . H2O is a neutron absorber, To get a controlled reaction The CANDU reactors needs expensive Heavy water ( D2O )
BY FAR the finest explanation of the fission dynamics of Uranium and Plutonium atomic bombs that I've ever seen. Thank you!
How the hell is this floating at 2k views? It’s an absolutely perfect explanation.
6.7k
Actually it over simplifies how they work. Especially the plutonium portion... it isn't quite as easy to make it because bombarding uranium with neutrons doesn't just make plutonium 239, it can also create plutonium 240 and plutonium 238, both of which don't well for making a bomb. Even the implosion bit is off because the shaped charges can't be made of a homogeneous explosive because you need to focus the explosives with slower explosives so the force pressing the ball is better equalized... otherwise you risk the explosive charges shredding the ball instead of compressing it... This is a good elementary school explanation but that's about it.
To clarify: a critical mass is when each fission causes one additional fission so the fission reactions stay at a stable rate (what happens inside a nuclear reactor), a subcritical mass produces less than one additional fission per fission event thus the reaction dying off, and a supercritical mass has more than one additional fission per fission event, so the reaction rate keeps growing. Nuclear bombs, when they detonate, create a highly supercritical mass so that the reaction rate accelerates extremely rapidly and fissions a large fraction of the uranium or plutonium present.
Thanks , it helped me win a reddit arguement.
Haha, that's the main reason I do what I do. Take that other redditor.
Omg why am I here for the same exact reason
LMAOO😂
8:30 Another clarification: Most plutonium 239 is created in nuclear reactors, where there are lots of neutrons flying around. Some of the Pu-239 formed will absorb an additional neutron forming Pu-240. This isotope of plutonium has a very high spontaneous fission rate, which means there are always extra neutrons flying around inside a chunk of Pu-239. As a result, you have to bring the subcritical pieces of a bomb core together very fast into supercritical mass before those neutrons can get the chain reaction going and blow things apart. This turns out to be much faster than a gun-type design can produce, so they had to switch to implosion. As a bonus, implosion creates a much denser supercritical mass and thus allows much more of the plutonium present to fission.
IIRC, Pu-239 also has a higher spontaneous fission rate than U-235, which didn't help. This made the gun-type plutonium bomb design almost impractically long to begin with, then they discovered the problem with Pu-240's fission rate, which made it impossible to make a gun-type bomb of any reasonable size. You can find pics online of prototype "Thin Man" plutonium bomb casings that they made before the spontaneous fission problem nixed the whole design. They're roughly twice as long as the Little Boy uranium bomb, and that still wasn't long enough to work.
This is so well made and explained, Thank you. My brain itch is finally gone :P
Thank you so much it really helped me on my project.
Fantastic video and very clear explanation, thank you!
Conventional PWR reactors run on about 5% enriched uranium. 20% enrichment is considered "high assay low enriched uranium" and is used in smaller naval reactors.
Not sure, but subs may use even more highly enriched uranium to keep the reactor small and easier to fit inside the pressure hull. Also, reactors for the newest subs are designed to last the life of the sub, so need more fissile uranium to start with in order to last the 40 or so years they expect the sub to be in service.
Excellent explanation!! Thank you!!
Just the explosive lens itself is an insane feat of engineering. Using geometry, and chemicals with different combustion speeds to turn outwardly expanding explosions into an inwardly collapsing implosion. Even mechanics of the neutron source at the center of the imploding core is also fascinating, and genius. For better or for worse, the people who worked on the original Manhattan Project were very very smart, to say the least.
Thanks what a great explanation on the difference between uranium and plutonium.
When it comes to enrichment, an important thing to keep in mind is that the difficulty lies in getting STARTED with enrichment. Once you get to 4-5% enrichment, you're basically 80% of the way there. You need massive numbers of centrifuges (if that's how you're enriching it) to get very low-enriched uranium. Once you have that, a very small number is all you need to keep going, using only as much power as a grocery store. While 4-5% is useful for a reactor, it's VERY difficult to locate and identify a facility converting LEU to HEU. You don't need massive power feeds or tons of floor space. A few dozen easily-concealed centrifuges is all you need.
Additional fact: the reason UF6 is used (other than being the only uranium compound that's gaseous as semi-reasonable temperatures and pressures) is the F is a compound that, by and large, only has one isotope found in nature and as such is one less mass difference to deal with.
Thank you! A very educational video.
Wonderful exposition.
Quick question. What are the favorable weight of the critical mass in terms of density and weight in kilograms?
Ok, but where does the first neutron come from that starts the chain reaction. Is there something like spontaneous nuclear fission in uranium/plutonium that releases neutrons ?
Google up "urchin".
The radioactive material contains neutrons. They’re always colliding in the nucleus. It’s compressed so that it’s a chain reaction instead of normal decay.
@@AMC2283 sorry but no. Again, google for "urchin".
This is an interesting description of the Teller-Ulam design for a thermonuclear bomb. At least public information indicates that this is a likely possibility for the thermonuclear bomb. Us human beings are really great at making tremendously destructive devices.
The Born-Oppenheimer approximation is central to understand how Nuclear Bombs Work. BO says nuclei move at least 1/2000 times the speed of electrons. Hence nuclear fusion begins when the electron temperature is high enough to activate D-D or D-T fusion.
Great video!:)
Why it's important to use U235 instead of U238 since both are radioactive?
Latter the explosive lens was simplified in a tubular explosive charge, using a solid oblate spheroid Plutonium pit, and thus achieving the same symmetric compression, but this arrange allow make smaller - in size; bombs, and so put 10 thermonuclear warheads in one ICBM.
on the left you see little boy, on the right you see fat boy. luv that quote
fat man
Fat man
Iron ore? Gaseous diffusion? Po-Be Neutron initiators?
Fantástico 👏👏👏
Im drunk asf & I understood this perfectly wtff lol I feel like I just unlocked a new knowledge😂
So it's gravity that separates the 235 from 238 ?
Not gravity, but mass.
Number of neutrons. Aka, atomic mass (different isotopes)
How do they manage to achieve a perfectly symmetrical explosion?
A symmetrical explosion was an extremely difficult question at Los Alamos. The basic problem is similar to squeezing an orange with your hand: juice squirts out in lots of places because the inward-moving compression is not symmetrical. The solution was to use two different explosive types, with different rates of burning. They are carefully shaped to create the "perfectly symmetrical explosion". (The details need a diagram which you can find elsewhere on RUclips". ) The difficulty resulted in testing the plutonium bomb at Alamogordo in July 1945, with the shaped charges, before dropping one on Nagasaki. The uranium bomb shot a uranium "bullet" into a uranium target. That was a much simpler design, and the Hiroshima bomb was of that type and was not tested before being used on Hiroshima.
For the Little Boy bomb, they used a literal 170mm smoothbore gun barrel to make the bomb.
@erickanter4090 yes, it was.
Seth Rogan's voice + Science = Success
i totally wouldnt be here if it wasnt for my curiosity of whats happening right now...
Where is red mercury used then
You can build uranium implosion bombs. You cannot build plutonium gun type bombs.
how some reactor like CANDU use U238 ?
Good question! The CANDU reactor uses unrefined uranium which still contains some U-235. It is this U-235 which is still central to its production of energy.
@@RealChemistryVideos The trick to make CANDU reactors work , and they use natural Uranium ( 0,7 U 235 and 99,3 U 238 )
is That U can not use normal Light water ( H2O ) . H2O is a neutron absorber, To get a controlled reaction
The CANDU reactors needs expensive Heavy water ( D2O )
That's what I forgot. Thanks!
(All jokes of course)
Sort it out
I'm taking notes for a friend who is a Tin-Pot Dictator.
I still don't understand. To much for me.
They don't... this is all theoretical.