What Do You Think?

Forrest M. Mims III

Because we amateur scientists are scattered around the world, the Internet provides a wonderful way for us to exchange ideas and ask questions.

The Society for Amateur Scientists provides various ways for us to share information and interact with one another. One way is to establish a presence on the recently begun SAS Community site. The Citizen Scientist provides ways for you to express your ideas, including letter to "Backscatter" and in feature and project articles.

Then there's basic e-mail, so much of which arrives at my PC that it tends to stack up. But sometimes there are gems to be found among the spam and the fluff.

Recently SAS Executive Director Shawn Carlson and George Hrabovsky exchanged a few e-mails discussing the recent North Korean nuclear test. I was in on their exchange and asked Shawn if I could share some of his comments.

First, some background: As this is written, the news media continues to release contradictory reports on the North Korean nuclear test on 9 October 2006. Because the seismic signals from the event suggest a yield of less than a kiloton, some reports suggest that the test was a dud. Yet the U.S. has conducted tests of nuclear devices with yields as low as 18 tons, as with the former Davy Crockett tactical weapon system. Did the North Korean's test a sub-kiloton device light enough to be launched by its long range missiles?

Figure 1. Theoretical P-wave travel times provided by the United States Geological Survey (USGS) for the magnitude 4.2 event in North Korea on Monday, 9 October 2006 at 01:35:27 UTC. According to the USGS, "This map shows the predicted (theoretical) travel times, in minutes, of the compressional (P) wave from the earthquake location to points around the globe. The travel times are computed using the spherically-symmetric IASP91 reference earth velocity model. The heavy black lines shown are the approximate distances to the P-wave shadow zone (103 to 140 degrees)." Courtesy of USGS.

There is also the possibility that the explosion was a hoax, a fake test conducted with less than a kiloton of TNT.

During his e-mail exchange with George and me, Shawn did some quick calculations and came up with this intriguing analysis:

Just a quick calculation. How big a hole would they need to fill with TNT to give 0.5 kiloton explosion and how many trucks would it take to transport the explosive?

0.5 kiloton = 500 tons. If this were water, the volume required would be 500 cubic meters since one cubic meter weighs one (metric) ton.

The density of TNT is 1.6 g/cm^3 (Don't ask how I know). So the total volume required would be about 500/1.6 = 313 cubic meters.

The size of the hole is found by 4/3PI R^3 = V so, to first order R = (V/4)^1/3 (Since PI = 3 to first order)

Thus, R = 4.3 m. This means that the required diameter would be a sphere less than 9 meters in diameter.

This sounds possible to me.

How much weight can a large truck carry? In the US the legal gross weight of a truck is something like 80,000 lbs. Allowing 10,000 lbs for the vehicle, it looks like the hole could be filled with fewer than 20 trucks loaded to US legal standards (and we know that the North Koreans would likely overload their trucks).

So the idea that this may have been a hoax by N. Korea can't be ruled out by this simple analysis.

Shawn

PS: Re the size of the explosion relative to their launch vehicle... US technology is, of course, much better. But the nominal yield of a warhead on a US ICBM is 400 kT or 800 times the reported yield of this device. Clearly, the N. Koreans have plenty of room for improvement. With a device this small, they would have to be right on target even if the target was fairly soft. They have a long way to go before we should be too worried.

In view of the seriousness of the North Korean claim, Shawn's analysis is intriguing. And yet while a hoax by the North North Koreans cannot yet be ruled out, neither can the possibility that they intentionally detonated a low yield device or that they experienced a dud.

You can learn more about how nuclear tests are differentiated from natural earthquakes here and elsewhere on the web.

If you know the science and are well informed about the relevant peripheral issues, share your views with the rest of us by beginning a discussion at the SAS Community site or in a letter to "Backscatter."

If nuclear physics isn't your thing, there are plenty of other topics available for study and discussion among amateur scientists. Consider William Appleby's article in The Citizen Scientist on the destruction of the airship Hindenburg ("Airship Hindenburg : Experimental study of the involvement of the outer covering paint (dope) in the disastrous final fire," 17 December 2004).

Bill's experiments support the original theory that the disaster was primarily fueled by the hydrogen gas that lifted the airship. But a recent theory advanced by advocates of hydrogen as an energy source is that the Hindenburg fire was triggered and then rapidly spread when the coating of the airship was ignited by an electrical discharge. A recent PBS program promotes this new theory.

What are your ideas? Read Bill's article. Then study the new theory about the flammability of the airship's coating. Did the airship company cover up its findings? If the new theory is correct, why did some pieces of coating survive the disaster? The sample ignited by a spark during the PBS program burst into flame, but it did not appear to burn completely.

Bright, creative and well informed amateur scientist have made countless contributions to the understanding of science. Can you make a contribution by expressing solid, thoughtful ideas about the North Korean nuclear test, the Hindenburg

disaster or a wide range of other topics? If so, the communication tools are available, and we're waiting to hear from you.