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View Full Version : How difficult is it to distinguish a thermonuclear explosions? (NK's "still not clear" one, e.g.)


Leo Bloom
09-14-2017, 08:57 PM
See query. Decades ago it was announced upon first news of a bang that India had thermonuclear as opposed to fission. It seems to me unbelievable that we (one, if one is the Pentagon) can be in doubt about that; the political or sources/technology-security issues for saying one thing or another is another topic, of course.

beowulff
09-14-2017, 10:26 PM
If the bang is big enough, it has to be thermonuclear, because fission bombs max out at about 1 MT.
If there's an airburst, it's a lot easier, since sniffers can pick up residual tritium and deuterium.

Duckster
09-14-2017, 10:56 PM
How do scientists determine if a nuclear blast has occurred? (http://science.howstuffworks.com/nuclear-detection.htm)
http://blogs.discovermagazine.com/crux/2016/01/06/how-scientists-detect-nuclear-explosions-around-the-world/

SamuelA
09-14-2017, 11:04 PM
Well, instead of pretending the government has magic or satellite sensors using no known technology, let's talk about what they could reasonably do.

1. The explosion itself creates a shock wave that can be heard through the ground. As beowulff points out, if the explosion is above a certain magnitude, it pretty much has to be a nuke. Above a certain level above that, and it pretty much has to be a thermonuclear device.

2. If some of the products of the explosion leak to the atmosphere, they could be sampled with a spy plane and from the isotope mix, it could be determined what type of nuclear reaction occurred.

3. If the explosion weren't hidden underground but were clearly visible, from the fireball I suspect it's possible to tell from timing and temperature, if a very large and expensive camera were aimed at it. Which would be difficult to mount on a satellite, wouldn't have enough resolution from space, and so on.

4. There may be exotic particle physics you can detect, but the detection equipment would probably have to be pretty close.

Riemann
09-15-2017, 01:18 AM
There was a second delayed seismic signal that may have indicated a tunnel collapse.
http://www.bbc.com/news/41139740
The US Geological Survey recorded a second event approximately eight minutes after the test. The USGS, as well as China, have assessed this event as a "collapse" of the cavity.
Why would the tunnel collapse? It could be that the tunnel was not constructed sufficiently to handle an explosion of that size. It's also possible that they intended for this collapse to occur - a way of signalling to the world that this was an authentic test through radionuclide release, a serious advance. It is still too early to tell.

And spy satellite pics of the site showed that a landslide had occurred.
http://www.bbc.com/news/world-asia-41170940

So there may be sufficient leakage of radionuclides to analyze the event. This could prove definitively that it was thermonuclear.

Leo Bloom
09-15-2017, 10:15 AM
[Air Force Gen. John E. Hyten, commander of Strategic Command], on whether the NK bomb was thermonuclear]: I have to make that assumption. What I saw equates to a hydrogen bomb. I saw the event. I saw the indications that came from that event. I saw the size, I saw the reports, and therefore to me Im assuming it was a hydrogen bomb.

Cite. (https://www.timesofisrael.com/us-nuclear-commander-assumes-north-koreans-tested-h-bomb/)

Well, so much for the political embargo.

watchwolf49
09-15-2017, 10:27 AM
Seismic waves from a nuclear explosion are very distinctive ... unfortunately the USGS seismographic network isn't "tuned" to register these waves ... however the USAF maintains a similar network that is explicitly "tuned" to these waveforms; mainly by setting up the military seismometers away from earthquake prone areas ... here's a blurb about AFTAC (http://www.25af.af.mil/Units/AFTAC.aspx) and what they do ...

What I don't know is if there are different waveforms for fission and fusion devices ... or if we're relying on beowulff's comment about the size of the explosion ... keep in mind that much of what AFTAC is doing is, you know, classified ... so even if the military could tell the difference, they're not going to be telling us they can ...

Blakeyrat
09-15-2017, 02:59 PM
Well, instead of pretending the government has magic or satellite sensors using no known technology, let's talk about what they could reasonably do.

1. The explosion itself creates a shock wave that can be heard through the ground. As beowulff points out, if the explosion is above a certain magnitude, it pretty much has to be a nuke. Above a certain level above that, and it pretty much has to be a thermonuclear device.

2. If some of the products of the explosion leak to the atmosphere, they could be sampled with a spy plane and from the isotope mix, it could be determined what type of nuclear reaction occurred.

3. If the explosion weren't hidden underground but were clearly visible, from the fireball I suspect it's possible to tell from timing and temperature, if a very large and expensive camera were aimed at it. Which would be difficult to mount on a satellite, wouldn't have enough resolution from space, and so on.

4. There may be exotic particle physics you can detect, but the detection equipment would probably have to be pretty close.

5. They might have reliable human intelligence assets (aka spies) on the ground that say it was thermonuclear, and they just say it was detected by technology in the public release as to not give them away.

Chronos
09-16-2017, 09:02 AM
The commander of Strategic Command pretty much has to assume that it's a real H-bomb whether it is or not, if there's even the slightest chance that it might be. It's his job to plan for the worst-case scenario. He also has to assume that it's not just a bomb, but a weapon, even though we've never had any evidence that North Korea has any sort of nuclear weapon. But they might, and that's enough to get people (especially people like Gen. Hyten) to lose sleep.

AK84
09-16-2017, 10:40 AM
There are basically four* kinds of nuclear devices

Pure Fission
Achieved from the fission of nuclear material; U-235/U-238

Boosted Fission
A small amount of Tritium is used just as fission starts, which increases the amount of materal which undergos fission; it also produces a small amount of fusion, but its a fraction of the total explosive force.

Layer Cake Fission/Fusion
A fission core, surrounded by layers of fusion followed by fission layer (U-238 not U-235). The Fission of the core starts a reaction in the fusion layer, which starts a reaction in the fission layer; about 15-25% of the explosive force comes from fusion, rest from the increased efficiency of the fission reaction.

True Multi stage
A fission primary sets off a fusion secondary.

The size of an explosion can give an indication, a high KT range weapon is likely to be a Boosted fission or layer cake device, a multi-megaton one, a Multi-stage one.


The NORK device was 120KT. The largest pure fission bomb tested was Ivy King (https://en.wikipedia.org/wiki/Ivy_King), 500KT. The largest pure fission bomb ever deployed was the French MR-31 (https://en.wikipedia.org/wiki/MR_31), at 120 KT (and this was deployed on a missile so was not particularly clunky).
So the tested weapon is within range for pure fission bombs. Its also within range for boosted fission/layer cake and although on the lower scale, Multi-Stage.

You can tell the difference between pure fission and the rest pretty easily by checking the particles produced. You might be able to tell the difference between boosted fission and Layer Cake/Multi-Stage. AFAIK, there is no way to tell the difference between Layer Cake and Multi Stage, except the larger yield ones will probably be Multi-Stage

*Ignoring neutron bombs.