I admit this may be the wrong place to ask this, but shouldn't it be relatively easy to tell if they really did it or not, since neutrino detectors would have (maybe) noticed the explosion?

Easier and cheaper, not to mention faster and more sensitive: Seismometers. CNN reports that S Korea reported such evidence.

Fred

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Neutrinos are extremely hard to detect. That´s not a suitable method for nuke detonation detection. Even the best solar and cosmic neutrino detectors can only expect to find a very small amount of them per year (a few tens of thousands).

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@BISMARCK
Hum,
there is no easy way to verify the north Korean claim.
But, perhaps the Russian stations can sniff out radioactive particles in a few days time.
If it turns out that they have, then it is quite remarkable that they have managed to do it in such a short time.

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As I understand it, the primary detection is seismic, and the signature of a nuclear explosion is different than that of an earthquake, though I recall that very small devices (I don't remember how small) might be below the detection level. There are also tests for airbourne products of a nuclear explosion, that leak out even from underground tests, but that those tests take more time.

This link is from The Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty Organization.
There is a link to their work on verification methods.
There is a lot more technical data on the website, though I could not find anything about the current "event".

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The seismic event occurred at the depth of 0 km, which makes it an obvious nuclear test man-made explosion.

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Science is a way of trying not to fool yourself. The first principle is that you must not fool yourself, and you are the easiest person to fool.
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The `test` took place in a disused mine, but it could of course (as has been said) just have been conventional explosives.
(some of you may recall the first US nuclear tests, which were recreated/forged (because of security fears) using conventional explosives for the media - the classic nuclear mushroom cloud that many websites show is just a conventional TNT explosion.)

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Well, it makes it pretty likely to be an explosion. There is some doubt as to whether it was nuclear or a large stockpile (200 cubic meters) of conventional explosives.

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Would an underground test completely hide the gamma ray signature?

All I can say that as a member of the National Guard, I've already taken my uniforms to the cleaners and organized my gear. Who knows?

Yes.

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South Korea detected an explosion ;va seismic recording equipment at 1.35 GMT. China confirmed this within an hour. The US Geo service sat on the fence until 3 pm GMT. denying the explosion had even happened for some hours. Why would that be..?
This is all in the off topic babbling.>>>>

Judiciousness?

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Reports are it was about half a kiloton, seems small, Maybe it didn't go Bang properly ot its a hoax?

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It could be a hoax, but if that turns out to be the case North Korea would lose its credibility. A failure is possible, but it is also possible that the cavity where the bomb was located was very large which would mean that the actual explosion was much bigger than the seismic event would suggest. Speculations abound.

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Science is a way of trying not to fool yourself. The first principle is that you must not fool yourself, and you are the easiest person to fool.
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I reckon the media got that one wrong because a Mag of 4.2 is not a 500 Ton explosion, it's much larger - more likely a few Kilotonnes
http://earthquake.usgs.gov/eqcenter/...kes/ustqab.php
If the Koreans tested their Nuke, they'd also want to save some for later. You weren't expecting the DPRK to blow all their nuclear material on one Big 20 Mega-Tonne bomb ?

Politics my friend, somebody was trying to keep a lid on this one and it does them good to keep their heads in the sand and deny an explosion ever took place - it helps reassure the public like those 1950s duck and cover videos, I won't get into it anymore because that would break the politics rule on this site.

I heard an analysis on National Public Radio that raised the same possibilites: a weapon that was supposed to be higher yield but wasn't (partial failure), a higher yield weapon that was masked, a small yield weapon, or a non-nuclear explosion, designed to look nuclear. They were leaning to # 1 or # 2, but were awaiting more data. I suspect that even the seismic data needs more analysis. This Reuters story discusses some of the same points.

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At night the stars put on a show for free (Carole King)

One Earth, One Sky - IYA 2009

The analysis may take a couple of weeks.

There is some speculation that one of the Pakistani nuclear detonations in 1998 was in fact a North Korean bomb.

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Science is a way of trying not to fool yourself. The first principle is that you must not fool yourself, and you are the easiest person to fool.
-- Richard Feynman

In answer to the original post, I can't help but think that the neutrino detectors should have detected something. After all, the neutrino detectors available in 1987 caught 11 neutrinos from a supernova explosion in the LMC, some 160,000 light-years away. If a nuclear explosion can create a significant number of neutrinos the detectors should pick up a few and be able to infer an approximate direction.

But can a nuclear explosion create neutrinos? Not in the explosion itself, that's primarily fission products, neutrons and gamma rays. But what of the fission products? Fission products tend to be neutron rich isotopes and so likely to decay quickly by beta decay. But how quickly? Aye, that's the rub. I don't know what the most common daughter nuclei are from plutonium-239 fission. If there is a fairly common daughter with a half-life on the order of seconds then there is a good chance of lots of neutrinos.

If the above scenario is true, then the neutrino signature of a (plutonium fission) nuclear explosion would be a burst of electron antineutrinos several seconds long with most arrivals in the first seconds. All of these neutrinos would be travelling in the same direction and the Cerenkov radiation in the chamber would illuminate one "wall", the one opposite the explosion.

Now I've got to look this stuff up somewhere without arousing too much suspicion ...

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The bar has been lowered for the promotion of ATM ideas; the bar for the acceptance of ATM ideas must remain high.

There has been several test after 1987 (see this image). Have neutrinos from these tests been detected?

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Science is a way of trying not to fool yourself. The first principle is that you must not fool yourself, and you are the easiest person to fool.
-- Richard Feynman