Knowledgeable DUers, my recollection, from a history paper I

[rzemanfl]

wrote quite a few years ago is that is HARDER to make a small nuclear weapon than a big one. Something to do with fractional critical mass, as I recall. I am I correct?

[hobbit709]

1. Easy to make big boom

harder to make small one. Takes more critical timing of detonator charges, increased neutron reflection into critical mass before it all flies apart.

[blm]

2. You're probably right. From what I recall about the suitcase nukes debate

they were still in development as of 2004, and Kerry had already been advocating against them for years and would have cancelled the program immediately upon taking office.

So, I would guess there must be a degree of difficulty making them that doesn't exist with the larger ones.

[Freedom_from_Chains]

3. I have heard that also but can't remember where. n/t

[htuttle]

4. Smaller in SIZE yes, but...

...it's not harder to make one smaller in yield than the multiple megaton ones that are currently in vogue in the nuclear club. The easiest one to make is the Hiroshima type one with the 'gun barrel' trigger. And that design only scales so large (in yield) before it becomes unworkable. Then they go to far more complicated design of the 'implosion' type ones with the expensive ultrafast microswitches, etc... that are used by 'modern' nuclear powers.

So, as I understand it, something around the 15-20kt range is not too hard, relatively speaking. Anything much larger or smaller is much more difficult (ie., such as both small nuclear artillery shells and huge ICBMs).

[hobbit709]

9. Megaton yields are fusion bombs

10-15 kiloton fission bombs are the low-end practical limit size. You can reach critical mass with smaller amounts of plutonium or uranium but the trick is to get enough neutron activity before the mass separates from the blast to stop the reaction. The main part of the physical size of the original bombs in 1945 was the shielding and casing-the amount of actual nuclear material wasn't much bigger than your fist.

[Xipe Totec]

5. Yes

The reason the USSR made it to space before we did was that we were better at building small nuclear weapons, so we did not need large rockets. The Russians, on the other hand, could not get the hang of building small bombs, so they had to build large rockets for delivery. Large enough, in fact, to carry humans as payload.

The reason we went to the moon was to level the playing field. The Russian rockets were not large enough for that trip, so everybody had to go back to the drawing board. We gambled that we could design a larger rocket before they did and, fortunately, our Germans were better than their Germans.

[htuttle]

7. "our Germans were better than their Germans"

Ain't that just the truth of it...

[Xipe Totec]

12. My favorite line from "The Right Stuff"

Delivered by Wernher von Braun.

[rzemanfl]

11. That all rings true with me. n/t

[sweetheart]

6. How hard can it be?

Isn't a nuclear weapon a glorified artillery shell,
firing a plutonium pitt in to a bowl to achieve critical mass?

Surely if that speed is not enough, the bowl can be fired back
at the pit simulaneously to double the kinetic energy... fancy
implosion timers and big mine-shaped spherical balls, is supposed
to be for the 'big' bombs, yes?

[Xipe Totec]

10. It's the other way 'round

Fancy implosion timers and big mine-shaped spherical balls are to make a smaller mass go critical.

You start with a sub critical mass and compress it until it becomes dense enough to become critical.

Criticallity is about making the mean distance between collisions smaller than the radius of the fissionable material. You can achieve this by making a larger ball of the stuff, or, by compressing the ball so more atoms get in the way of the escaping neutrons.

[Finder]

8. Depends what type...

What is called a dirty bomb for example is merely a conventional bomb that disperses radioactive material...still considered a nuclear weapon by most but is not like a fusion/fission device.