Wish to understand atomic weapons

[eggman]

I also wish to understand atomic weapons...

The TV said Iran can build a 'device'...

I read here at the forum that Nuclear plants are limited to 5% pure fuel...

I assume an H-bomb is more than 5% pure fuel...

Is the media just trying to spook us?

Also if my research is correct..it takes huge amounts of raw material to even make a mini a-bomb...

...please explain the various states such as critical mass...sub critical...super critical...etc...

 

[Hootenanny]

A good book to get hold of would be 'The Los Alamos Primer' which contains the original lecture notes annoted by Robert Serber himself. I've read this book before, but unfortunately forgot most of the material. However, I think this is Astronuc's field of experties.

As for the 5% pure limit, I believe that is a saftey precaution to help prevent a massive chain reaction (as in chernobyl).

~H

 

[eggman]

I have the movie 'Trinity and Beyond'

which is very fascinating...man has unleashed the ultimate power in the universe it appears...

Kinda spooky...kinda awesome

 

[ZapperZ]

Er... Please don't use a "movie" as a valid source, or even something you use to base your opinion on here in the physics section of the forum.

zz.

 

[eggman]

ok...found the book

thanks

 

[rcgldr]

Purity has to go from around 5% to 80% to make weapons grade U235.

 

[pervect]

Note that an undergraduate physics major designed a "creditable" nuclear bomb. It really isn't that hard to do. Getting the materials, bulding and testing one is still a major project for a government (and not an individual). However, nobody should doubt that a government (like Iran) could implement a successful program to build nuclear weapons if they feel threatened.

For a specific example see
http://en.wikipedia.org/wiki/John_Aristotle_Phillips

#pragma irony
Of course, I don't see how Iran could possibly feel threatened by any of the actions of our current administration. Why would they go to the trouble and expense of building a "device"?

 

[eggman]

Religion/Politics seem always to feel threatened...

thats the fuel for their egocentric self centered

exsistance...

 

[eggman]

in the movie H-bombs have liquid fuel...

and i am sure its not Drain-O

 

[eggman]

uh oh...that was philosophy...me in trouble again..(?)

 

[Astronuc]

One certainly needs more than 5% U-235, the naturally abundant fissile isotope of uranium, to produce a nuclear weapon. One preferably tries to make the u (in metal form) as close to 100% as possible, but because that is prohibitively expensive 80-90% is usually sufficient.

Natural uranium (from the mine) has about 0.71% U-235, 99.245% U-238, with some U-234. It is used in CANDU Heavy Water Reactors without enrichment, so the Iranian could use CANDUs.

Light Water Reactors (LWRs in the West and Russian VVERs) require enriched uranium). The current licensed limit (i.e. authorized by varies national governments) is 5.0%. Some research reactors use 20% or higher.

The CANDU and LWR fuel is in the form of UO₂ encapsulated in long tubes of a Zr-alloy and sealed at both ends. The water coolant serves to cool the fuel and moderate it. The CANDUs use heavy (deuterated) water, so there is less moderation than in LWRs. The LWRs require higher enrichment to overcome the absorption of neutrons by H in the water (deuterium is used in heavy water to avoid this matter).

Anyway - getting back to nuclear weapons. Uranium could be used in gun type similar to Little Boy (http://en.wikipedia.org/wiki/Little_Boy) .

More modern nuclear weapons use an implosive geometry, and preferebly Pu 239, because Pu-239 has a higher cross-section for prompt neutrons and allows a smaller critical mass. Pu-239 is used in 'triggers' for thermonuclear weapons.

Pu-239 is produced by virtue of neutron capture in U-238, which becomes U-239, and then through two successive beta decays becomes Pu-239. Pu then must be separated chemically from the U, purified and formed into a metal of the appropriate geometry.

So far the discussion concerning Iran is focused on the potential to enrich uranium to greater than 5%, which they could do in theory.

For every kg of U-235, one need ~140 kg of natural U. Uranium bearing ores contain about 2-3% uranium or, so one needs tons of ore from which to extract uranium. Iran apparently has its own deposits, so it makes sense for them to develop nuclear power, IF they do it for peaceful purposes.

 

[Mk]

Deuritium is an isotope of hydrogen.

More modern nuclear weapons use an implosive geometry, and preferebly Pu 239, because Pu-239 has a higher cross-section for prompt neutrons and allows a smaller critical mass. Pu-239 is used in 'triggers' for thermonuclear weapons.

What does implosive geometry mean?

 

[Pengwuino]

There is a pretty good book for the semi-layman that i read last year that a professor recommended to me. It was written by a guy who actually is/use to be a high school teacher but the book was great nontheless. He had written a series of kind of "physics topics for dumbies" if you wish books that were used in some university lecture courses. I don't remember the name of the book series though! It was something like "A not too complicated look into nuclear energy" or "Not too serious look into nuclear energy" or something. I liked it because it wasnt really a science textbook but it went a little beyond just normal reading material because each topic had a few questions like textbooks do. One chapter talked about E=mc^2 and then had questions in the end on usinig such a formula. Neat book, can't remember the damn name though

 

[Tide]

What does implosive geometry mean?

It means that you assemble a critical mass from subcritical components at the time of detonation. You should be aware that additional details may not be suitable for public discussion.

 

[Mk]

It means that you assemble a critical mass from subcritical components at the time of detonation.

That sounds a lot more complicated—why is it done? Is it more fruitful?

You should be aware that additional details may not be suitable for public discussion.

Oh poo, does that mean I'm going to have to work hard to get the answer instead of ask you? frowny face -->

 

[Hootenanny]

That sounds a lot more complicated—why is it done? Is it more fruitful?

What would happen if you had the critical mass of a fissile material?

~H

 

[Astronuc]

What does implosive geometry mean?

Basically it is a round geometry, essentially spherical, that allows a sub-critical geometry to be compressed into a critical geometry very rapidly.

It is the principal behind the "Fat Man" bomb dropped on Nagasaki during World War II. http://en.wikipedia.org/wiki/Fat_man

As Tide indicated, the details are absolutely not appropriate for public discussion.

What would happen if you had the critical mass of a fissile material?

There was an unfortunate accident back in 1945 involving Louis Slotkin and a critical mass assembly. The assembly consisted of two hemisphere of uranium (mostly U-235). With one hemisphere fixed, Slotkin would lower (holding it with two screwdrivers) the upper hemisphere toward it while monitoring the activity with a radiation detector. Unfortunately, one time, the screwdrivers slipped and the upper hemisphere combined with the lower in a critical mass - and it went critical. Slotkin stuck his hands in and pried apart the assembly, but in doing do he received a massive dose of neutrons and gamma-rays.

Within an hour, Slotkin had lost his sense of touch. Gamma rays had penetrated his skin, and had destroyed his sensitive nerve cells first. This was an unexpected gift, because it spared Slotkin the horror of being conscious of his own death -- by the end of the day he had become delirious.

Over the nine days it took Slotkin to die, his hair fell out and the number of white corpuscles in his blood skyrocketed. His skin, both internally and externally, started coming off in layers. To put it simply, his cells lost their differences -- before long, there was no way to distinguish a liver cell from an intestinal cell from a blood cell. When he died, it was determined that the muscles of his heart were nothing but a mass of torn fibers.

quotes from http://www.gettingit.com/article/165

This is pretty much as it is described in other sources.

 

[eggman]

please explain in laymans terms 'it went critical'

thanks

ps:are u saying that if Louis had not 'pried it apart' it would have detonated ?

 

[Astronuc]

please explain in laymans terms 'it went critical'

are u saying that if Louis had not 'pried it apart' it would have detonated ?

Critical means that the number of neutrons increases exponentially with time. Had Slotkin not separated the assembly, it would not necessarily have exploded, but it would have produced a lot of radiation. I believe one or two others were also severely irradiated, and IIRC one died.

Most likely the critical assembly was not 'prompt' critical (i.e. subsequent fissions are induced entirely by fast neutrons released from fissioned atoms), otherwise it would have 'exploded', but the yield would have been relatively low. It was more likely critical with some delayed neutron component, which is what allows us to control nuclear reactions in nuclear reactors. There are mitigating factors such as neutron leakage from the assembly and the fact that as energy is produced in the metal critical assembly, it would heat (or melt) and thermally expand which would cause it to go subcritical.

Nuclear weapons are designed to be prompt critical, and that is facilitated by increasing the density of the fissile material.

 

[3trQN]

Basically it is a round geometry, essentially spherical, that allows a sub-critical geometry to be compressed into a critical geometry very rapidly.

When you say compressed, what kind of pressures are we talking about? Having recently read about the diamond anvil and it obtaining in the order of 10^6 Atm of pressure, i wondered what mass of fissile material would be required to achieve criticallity at those kinds of conditions. Maybe I am too curious lol. I lack the knowlage to do the calculations myself.

http://en.wikipedia.org/wiki/Diamond_anvil

 

[Astronuc]

The pressure is pretty high. That's about all that can be said. The policy regarding nuclear weapons technology is that it is not discussed in the public domain, despite the fact that much has been published (not all of it correct).

 

[eggman]

according to a page i found on the internet...u could cause a paper clip

to go off like and atomic bomb if u squeezed it hard enough...

something like the pressure at the center of the sun...it was pretty extreme...

: )