Basic question:
Why would a nuclear explosion creat a wave or “EMP’”
-Regards
what is a electral magenetic pusle…why is one created
Hi There! Electro magnetic pulse is a short, intense wave of electrons thrown out by the detonation of an atomic bomb, especially when detonated in the atmosphere. The gamma waves created as part of the nuclear chain reaction excite nitrogen and oxygen molecules and release large quantities of electrons. These electrons travel away from the source of the explosion until they find conductive material, run down it, and overload your television. Then, while you’re thumping on the side of it wondering what happened to Gilligan’s Island, the blast wave arrives, flattens your house and irradiates you and your family. Have a nice day 
http://www.campusprogram.com/reference/en/wikipedia/n/nu/nuclear_weapon.html
http://www.physics.northwestern.edu/classes/2001Fall/Phyx135-2/19/emp.htm http://www.globalsecurity.org/military/library/news/2003/02/mil-030214-usmc05.htm
Sorry to be nitpicky but you’d be irridated by gamma rays before anything else gets to you.
Like a clock ticking on a time bomb
Its traditional , you gotta have it
Declan
No. It’s not the electrons liberated by gamma interactions that carry teh destructive energy of the EMP, it’s the intense electromagnetic field these liberated electrons generate via the Compton effect (per your cites) that are responsible. This electromagnetic field, in turn, induces large voltage potentials across any electrical conductors that intesect it, which drive proportionally large currents through those conductors. It is these currents which do the damage to electrical and electronic equipment within the the scope of the EMP.
An electromagnetic pulse, is a pulse/flash of electromagnetic radiation in the gamma ray part of the spectrum. From low to high frequency it goes; radio waves, microwaves, infrared, optical light, ultraviolet, x-rays, and finally gamma rays.
The EMP gives rise to a giant electric field that is created by ionizing the air (nitrogen and oxygen). The light we see with interacts with atoms in the same way gamma rays do. When a photon (a particle of light) hits an atom, it is absorbed by one of its electrons. This electron jumps an orbital (moves a little further away from the nucleus of the atom), and then usually moves back and emits another photon identical to the one that it absorbed. Gamma rays are so powerful though, that when an atom like oxygen or nitrogen absorbs one of these high energy photons, the electron move so far away from the atoms nucleus that it is basically ripped from it.
Think of one of those balls that is attached to your hand by an elastic string, as opposed to an electron attached to an atoms nucleus by positive/negative attraction. When you add energy to it (throw it), it moves away from your hand but then comes back. To much energy though and the ball won’t come back.
No. What youa re describing is a gamma ray burst, which is really bad for organic matter, but has almost no effect on electronics, except to the extent that certain types of semiconductor devices can be affected. An EMP is a broadband EM pulse, covering a good bit of the EM spectrum. The part that does the most damage to electrical and electronic devices is usually the mid- to upper-range RF, which induces the largest voltages for a variety of reasons, including the fact that circuit paths are typically of such a length as to make efficient antennas at these wavelengths.
You’re quite correct about that, I was trying get the ball rolling with answers and not muddy the waters with such fripperies as facts.
Plus - one kudo will be awarded to the first person to identify the film reference in my original reply.
[nitpick]
That’s not quite the role of the Compton effect in the process. The gamma ray photons knock the electrons out of the atoms in the atmosphere - it’s this that’s via the Compton effect. These electrons now have large kinetic energies and so stream away from the centre of the explosion, leaving behind charged ions. In the first 10[sup]-8[/sup] s after detonation a negatively charged radial current is therefore set up around the centre.
Asymmetries in the process then mean that this current transmits the EMP - essentially like the current in a giant, shortlived, immensely powerful radio aerial. The power involved is so vast that the asymmetries don’t have to be very big to produce a pulse. Even things like differencies in the density of air at different altitudes are enough.
As usual, lots of details in Glasstone and Dolan, The Effects of Nuclear Weapons, in this instance in Chapter XI.
[/nitpick]
Gamma from: Popular Mechanics
“The detonations created bursts of gamma rays that, upon striking the oxygen and nitrogen in the atmosphere, released a tsunami of electrons that spread for hundreds of miles.”
Gamma from: http://www.fas.org/nuke/intro/nuke/emp.htmrays from the nuclear reactions within the device. These photons in turn produce high energy free electrons by Compton scattering at altitudes between (roughly) 20 and 40 km. These electrons are then trapped in the Earth’s magnetic field, giving rise to an oscillating electric current. This current is asymmetric in general and gives rise to a rapidly rising radiated electromagnetic field called an electromagnetic pulse (EMP). Because the electrons are trapped essentially
“A high-altitude nuclear detonation produces an immediate flux of gamma simultaneously, a very large electromagnetic source radiates coherently.”
Gamma from: http://www.geocities.com/Area51/Shadowlands/6583/project155.html
“The formation EMP begins with the very intense, but very short burst of gamma rays caused by the nuclear reactions in the bomb. About 0.3% of the bomb’s energy is in this pulse, but it lasts for only 10 nanoseconds or so. These gamma rays collide with electrons in air molecules, and eject the electrons at high energies through a process called Compton scattering. These energetic electrons in turn knock other electrons loose, and create a cascade effect that produces some 30,000 electrons for every original gamma ray.”
Gamma from: http://www.physics.northwestern.edu/classes/2001Fall/Phyx135-2/19/emp.htm
“An electromagnetic pulse starts with a short, intense burst of gamma rays produced from nuclear detonation. The gamma rays interact with the atoms in air molecules through a process called the Compton effect, wherein electrons are scattered at high energies, thus ionizing the atmosphere and generating a powerful electrical field. The strength of the EMP depends highly on the altitude at which it is released. At altitudes above 30,000m, it is the strongest. It is also significant at surface or low altitude bursts, but is not as effective between the two extremes.”
Radio from: Wikipedia
In telecommunication, the term electromagnetic pulse (EMP) has the following meanings:
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The electromagnetic radiation from an explosion (especially nuclear explosions) OR an intensely fluctuating magnetic field caused by Compton-recoil electrons and photoelectrons from photons scattered in the materials of the electronic or explosive device or in a surrounding medium.
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A broadband, high-intensity, short-duration burst of electromagnetic energy.
Note: In the case of a nuclear detonation, the electromagnetic pulse consists of a continuous frequency spectrum. Most of the energy is distributed throughout the lower frequencies between 3 Hz and 30 kHz.
Radio from: Wikipedia
“HERF or High Energy Radio Frequency weapons, also known as HPRF or High Power Radio Frequency weapons are weapons designed to use high intensity radio waves to disrupt electronics. They operate in a similar way to EMP devices, by inducing destructive voltage within the electronic wiring. They are usually directional and can be focused on a specific target.”
Im confused. It seems like when EMP is mentioned, people either talk about gamma rays causing the disruption or radio waves causing the disruption, but never both.
Oh, and… the word EMP has more definitions than I thought. I guess it could be considered the photon or electron part of the phenomena.
Yes, it’s a very complex topic. However, I didn’t mean to imply that gamma rays had no role in the production of a nuclear EMP, only that they aren’t directly responsible for the damage to electrical systems. Yes, gamma rays are a form of electromagnetic radiation like radio and light, and I imagine that’s where some of the confusion arises.
If the gamma rays cause the release of the electrons, the gamma rays would lose energy in the process, wouldn’t they? So, do the gamma rays become something else (i.e.: taking on a lower energy level?) Or, do they remain as gamma rays?
- Jinx
Yes, the gamma ray photons do lose energy when they scatter off the electrons, knocking them out of the atoms. However, they’ll only lose a relatively small fraction of their energy and so most of them will still be gamma rays.
Just to clarify a bit:
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It’s an electromagnetic pulse, not an electron pulse (cf. cabdude’s post). So it reaches the “target” at the same time as all the other photons. (Ignoring some tiny effects.)
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EMP weapons are in quite advanced stages of development all over the world. These don’t use nukes. So you don’t need gamma rays, etc. to generate them. Nukes are obviously better than conventional weapons at this (and at causing a lot of other damage), but people seem a lot happier when you drop a conventional weapon on them for some reason. This is implies that there is a lot of research on “hardening” military systems against EMPs. If you know quite a bit about the physics of such stuff, the US DoD will throw piles of money at you to work on it.
Yes - I definitely gave the impression it was a pulse of electrons - not a pulse of electromagnetic energy generated by the release of electrons :smack:
And STILL no one wants to quote the obvious movie reference.
slight hijack:
is it possible to do what that fellow did in Ocean’s 11, where he used an EMP wave to knock out all the electricity in vegas for less then a minute?
Well, in the good version, they used small explosives to knock over some transmission towers. No EMT needed. In the bad version… well it was bad in every way, shape and form including every single technical detail.
To knock out power to a city like Las Vegas using a conventional EMP you would need to:
- Do a single explosion that would be on a near-nuclear scale. The immediate physical damage would kill thousands, topple buildings as well as permanently ruin a lot of electronics. Nothing within range would ever work again. Once something is fried, it stays fried. Fuses and cicuit breakers aren’t even in the same class of stuff needed to provide adequate protection.
or
- A lot of small explosions at key locations like substations. Fewer (but not 0) deaths, not nearly as much damage, and only stuff within a block of each explosion would be fried. It would in fact just be easier to do it like in The Good Version.
(Okay, the good version did use the “cross the wires” gimmick, but that’s nothing compared to the bad version.)
It’s not too difficult, actually. Unlike for radiation hardening, where you need thick shielding of lead or similar material (very heavy, to put on aircraft), for EMP shielding all you need is a good conductor. I wouldn’t be surprised if superconductors (together with the requisite cryogenic systems) are used in many pieces of military hardware, and I would be surprised if they don’t at least use silver.