nuclear-engineeringnuclear-physicsradiation
How can we know that North Korea and Iran (to name a few) are exploding nuclear weapons if no inspectors have ever been granted access to suspected nuclear sites in these countries?
How can we passively detect a secret detonation of a nuclear warhead? What are the telltale signs of a nuclear detonation?
There are bigger things one can collect relating to nuclear weapons. How about this big chunk of metal from the Trinity site in 1945? http://www.panoramio.com/photo/53676180 Near an engineering school full of people smart at physics, no one is concerned about radiation from this. It wouldn't be on public display if it had any measurable radiation much above background.
In either case, your coin or Jumbo, it's not the unstable fissile material but part of the (former) container or shell surrounding the dangerous stuff. Yes, a few particles from the nasty core may have kicked some iron and other atoms into unstable isotopes, but not enough to be a problem.
You get more radiation from flying in a jet at 35000ft or eating a banana, or just standing there since your body naturally contains carbon 14, potassium 40, and other nuclear goodies.
Perhaps someone with more expertise on radiation and its health effects could kindly give more precise numbers than "a banana". But wikipedia (at the moment) does state this: "In a human body of 70 kg mass, about 4,400 nuclei of 40K decay per second."
Also, just to become familiar with radiation amounts in everyday (and noneveryday) life, see this infographic: http://xkcd.com/radiation/
Never underestimate the power of googling.
I googled "high speed nuclear explosion photos" and got a large number of them. Here is one:
This image captures two common elements: the spikes (called "rope tricks") and an uneven surface shape
The duration of the exposure is typically 10 nanoseconds
At this stage of the detonation the surface of the fireball has a temperature of 20,000 degrees, three times hotter than the sun's surface. At such temperatures the amount of thermal radiation (light) given off is so enormous anything it touches is vaporized ahead of the expanding fireball. The three spikes in this image result from the guide wires supporting the tower on which the bomb was located absorbing enough heat to turn into light emitting plasma. Because thermal radiation travels faster than the fireball, the spikes extend out ahead of it.
p.s. I should have remembered one frame cameras, since I had been using "gun cameras" from WWII to get images of cosmic rays in spark chambers by triggering, back in 1967.
Best Answer
There are many ways to detect a nuclear explosion, and there are people working to detect it. The Comprehensive Nuclear-Test-Ban Treaty Organization or CTBTO is one such organization. They are using a global network called the International Monitoring System. This is capable of detecting any nuclear detonations anywhere on the Earth (underwater, or in the atmosphere, or deep underground).
First of all, please note that a nuclear explosion releases a lot of energy, and I mean a lot of energy. Ionizing radiation, shock-waves, and heat are all generated in a nuclear explosion.
Let's talk first about how to detect shock waves from a nuclear detonation. These waves can travel through the air, water, and ground at the relative speed of sound in each medium. The CTBTO use an Infrasound Monitoring System to detect shock waves traveling through the atmosphere. Infrasound is generated in exploding volcanoes, earthquakes, meteors, storms and auroras; nuclear, mining and large chemical explosions, as well as aircraft and rocket launches in the man-made arena. Nuclear generated shock waves in the air are easily detected since a nuclear explosion is much much more powerful then pretty much anything else in the natural world.
Underwater nuclear explosion can be detected using a Hydroacoustic Monitoring System. They are kind of microphones at the bottom of the ocean. Theses microphones also pick up sounds from underwater earthquakes, underwater volcanoes eruptions, submarines, whale, and of course, nuclear detonation. Like an above ground explosion, nothing beats nuclear generated shock waves in terms of intensity. Therefore, an underwater nuclear explosion is also quite easy to detect.
Underground nuclear detonations can be detected using seismometers. Seismometers are used mainly to detect earthquakes. Different from the Infrasound Monitoring System, which detects sounds in the air, seismometers detect sounds in the ground. Scientists have documented the various characteristics of shock waves created by earthquakes to volcanic activities to even planes crashing. Thus, if powerful unrecognized waves are detected, they can link their observations to nuclear detonation.
Shock waves can be detected by multiple sensors as described above. Scientists can use this result to triangulate and correctly pinpoint the site of a nuclear explosion. This is how we know that North Korea secretly detonated nuclear weapons in 2006, 2009, and 2013.
Lastly, to be sure if an explosion is nuclear, scientists need to confirm the presence of a radioactive dust cloud using Radionuclide Detection. However, in the case of a perfectly contained nuclear detonation, radioactive dust cannot be detected. Therefore, teams of inspectors have to be sent to the suspected site.