Can we extrapolate the strength of NK's nuclear device from it's seismic magnitude?

[preslove]

As you all probably know, North Korea detonated a nuclear device. It's been reported as being picked up as between 3.58 and 4.2 (nytimes says the latter) on the richter scale. Can we infer the strength of the weapon in kilo/megatons from this data?

 

[DrPizza]

I'd believe we could... from wiki 4.0 on the Richter scale is a small atomic bomb; smaller than the one exploded at Nagasaki.

 

[f95toli]

The bombs that exploded at Nagasaki and Hiroshima WERE small, 15-20 kT which is similar to what you would find in a small tactical nuke today. If the bomb NK detonated really was even smaller than that something must have gone wrong.

 

[AstroGuardian]

I thought that nuclear devices aimed to kill were not allowed and no one would be fullish to try one again?

 

[f95toli]

I just saw a figure: 800 tons!
That is a tiny nuke, either I am missing something or their yield was very low.
I don't think it is possible to build a bomb that small with a reasonable yield, a 800 ton bomb with e.g. 90% yield would be too small to sustain a chain reaction.
Or am I missing something?

.

 

[Gibsons]

Originally posted by: f95toli
I just saw a figure: 800 tons!
That is a tiny nuke, either I am missing something or their yield was very low.
I don't think it is possible to build a bomb that small with a reasonable yield, a 800 ton bomb with e.g. 90% yield would be too small to sustain a chain reaction.
Or am I missing something?

.

A conventional sized, but really inefficient weapon might yield that low?

 

[gsellis]

Little Boy as an U-235/U-238 critical mass bomb (Hiroshima/Trinity site). When the core and plug were slapped together, they were just above critical mass. There yield is about as low as you go with a Uranium device. With Pu, Fat Man was about as low as you go.

Sounds like NK screwed it up or made the world's largest fertilizer bomb in attempt to pretend they are more important than they are. Too hard to tell because both are quite possible. No satellite I know of can detect post-event radiation. We will need human inteligence to determine what it was in most likelihood. I think the sesmic spike would be the same for real/not real.

 

[Calin]

Originally posted by: gsellis
Little Boy as an U-235/U-238 critical mass bomb (Hiroshima/Trinity site). When the core and plug were slapped together, they were just above critical mass. There yield is about as low as you go with a Uranium device. With Pu, Fat Man was about as low as you go.

You can go lower than that - in the realm of artillery-fired nuclear devices (tactical-scale), or anti-submarine nuclear tipped rockets. In the first case, one would like to have a range of a mile or so. In the second case, the shock wave (which is transmitted quite well thru water) must not destroy the firing vessel (again, a mile or so around the explosion point).

 

[JSSheridan]

Dr. Pizza, I didn't think the Richter scale was being used anymore. I think they are all Moment magnitude scale.

This seems like a black box problem. We know what the outputs are, but we don't know the input to the system. Now we've estimated the input, but we still don't know the nature of it.

 

[f95toli]

Calin: Sure, but even small tactical nukes usually have an explosive power of a few kTons AFAIK. I know there are "bunker busters" which are smaller but AFAIK they achive this by essentially "wasting" fissinable material on purpose (I think this is called "dial-a-yield") which I guess results in a pretty dirty bomb.

Moreover, I doubt NK would want to waste their limited stock of plutonium just like that.

Anyway, a 800 ton bomb will hardly impress anyone.

 

[DrPizza]

It's been reported as being picked up as between 3.58 and 4.2 (nytimes says the latter) on the richter scale.

According to the original post, they still are.

The moment magnitude scale and the richter scale give approximately the same value anyway (except for very large earthquakes.)

 

[BrownTown]

depending on which number you believe (3.58, 4.2, others) the bomb was several hundred tons to a few kilotons. Basically its tiny, but still VERY dangerous if it goes off in the wrong place. I would bet that North Korea was not able to compress the critical mass quick enough, or was not able to seperate the PU-239 from the PU-240 efficiently enough to get a clean explosion, and that the core partially fissiled greatly reducing the yield.

 

[dkozloski]

We'll know soon enough. There was no point in testing the device without the corresponding chest pounding. Just like a kid with a big fire cracker. He's got to brag.

 

[BrownTown]

yeah, i'll deffinitely trust whatever number North Korea comes up with ...

 

[PottedMeat]

Originally posted by: dkozloski
We'll know soon enough. There was no point in testing the device without the corresponding chest pounding. Just like a kid with a big fire cracker. He's got to brag.

... You think he'll blow off some of his fingers too?

 

[dkozloski]

At the Trinity test in 1945 one of the scientist observers dropped a fragment of paper as the shock wave went by his observation point. He saw how far the paper was displaced horizontally in it's downward flight by the shock wave and estimated the force of the blast within 2%. There were some pretty smart folks working on that project.

 

[Gibsons]

Originally posted by: dkozloski
At the Trinity test in 1945 one of the scientist observers dropped a fragment of paper as the shock wave went by his observation point. He saw how far the paper was displaced horizontally in it's downward flight by the shock wave and estimated the force of the blast within 2%. There were some pretty smart folks working on that project.

That was Fermi, IIRC. Smart guy indeed.

 

[dkozloski]

Originally posted by: Calin

Originally posted by: gsellis
Little Boy as an U-235/U-238 critical mass bomb (Hiroshima/Trinity site). When the core and plug were slapped together, they were just above critical mass. There yield is about as low as you go with a Uranium device. With Pu, Fat Man was about as low as you go.

You can go lower than that - in the realm of artillery-fired nuclear devices (tactical-scale), or anti-submarine nuclear tipped rockets. In the first case, one would like to have a range of a mile or so. In the second case, the shock wave (which is transmitted quite well thru water) must not destroy the firing vessel (again, a mile or so around the explosion point).

Even at a distance of a more than a mile the firing ship had to have the bow pointed in the direction of the blast to prevent damage from a nuclear depth bomb. Been there. Incidently the blast is throttlable(variable yield).

 

[rgwalt]

GI Taylor estimated the yield of atomic blasts from pictures alone (with length scales).

R

 

[dkozloski]

The story now is that it's either a dud or a hoax. Very interesting.

 

[judasmachine]

The tactical nukes known as suitcase nukes can have a yield of 0.2kt to 1kt. This would barely be stronger and more effective than a 'dirty bomb.'

 

[BrownTown]

No, a dirty bomb is purely conventional, so a huge one might be 1000 lbs, whereas a tiny nuke is still 400,000 lbs (equivilent).

 

[sillycheesedude]

sounds like tnt to me

 

[Sc4freak]

Originally posted by: judasmachine
The tactical nukes known as suitcase nukes can have a yield of 0.2kt to 1kt. This would barely be stronger and more effective than a 'dirty bomb.'

Barely stronger? Sorry, but I don't know of anyone who can carry 1000 tons of TNT in their suitcase. Dirty bombs are primarily designed to spread radiation, the small explosion due to the high explosive is merely a bonus. The damage done by a few kilograms of TNT is miniscule compared to even the smallest of nuclear weapons.

I highly doubt that it was just conventional explosives which caused a blast with a 0.5-2kt yield. Even 'only' 500 tons of TNT is a lot to gather and detonate all at once. More likely NK sucessfully tested a very low yield bomb, or their bomb didn't work at the expected efficiency.

 

[gsellis]

Originally posted by: Sc4freak

Originally posted by: judasmachine
The tactical nukes known as suitcase nukes can have a yield of 0.2kt to 1kt. This would barely be stronger and more effective than a 'dirty bomb.'

Barely stronger? Sorry, but I don't know of anyone who can carry 1000 tons of TNT in their suitcase. Dirty bombs are primarily designed to spread radiation, the small explosion due to the high explosive is merely a bonus. The damage done by a few kilograms of TNT is miniscule compared to even the smallest of nuclear weapons.

I highly doubt that it was just conventional explosives which caused a blast with a 0.5-2kt yield. Even 'only' 500 tons of TNT is a lot to gather and detonate all at once. More likely NK sucessfully tested a very low yield bomb, or their bomb didn't work at the expected efficiency.

Want to bet? It is just a manpower thing to put lots of ammonium nitrate and diesel together. They have plenty of slave labor in NKPR. The materials are easy to get and make. Much easier to rig that to blow.

I still suspect that it was a dude that could not sustain the reaction long enough. Probably tried an implosion device. Considering the satellite photo on Drudge of lights at nights, not sure I would put a lot of stock in NKPRs infrastructure. They can't even get a delivery system to run to the final target. Bet that little troll executed those folks too. That would sure motivate them by killing to folks who have a possible chance of pulling it off.