Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: taregg on 24/03/2014 18:32:18
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does x ray involve thermal radiation.......and why
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I'm not sure what you mean. X-rays can could be produced by thermal radiation if you get really hot. You can figure out a black body spectrum of emitted electromagnetic radiation for any temperature and at some hot-enough point, X-rays will start being produced. (You can get them from the sun, for example.)
It is far, far more efficient to produce X-rays by firing electrons at a target (not to mention that getting sources hot enough to efficiently emit X-rays is impractical). As electrons hit the target and slow down, they emit X-rays in a far more efficient way than by heating the target.
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It's all the same stuff - electromagnetic radiation. X-rays just have a higher energy (5 keV upwards) than infrared radiation (< 1 eV).
When we produce x-rays by bombarding a target with electrons, at say 100 kV, only about 1% of the incident energy is emitted as x-radiation (the efficiency increases at higher energies, but generating an electron beam above 500 kV is not an energy-efficient process!) and nearly all the rest of the electron beam energy is converted to heat, so we do get a significant amount of infrared out of an x-ray tube. Once you have produced an electron beam by whatever means, the most efficient conversion of electron energy to x-ray photons is to bend the beam in a magnetic field: this produces plenty of x-rays and very little heat but it's only practicable in large machines like synchrotorons, so we still use tungsten targets for most medical and industrial radiography.
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Are there any small X Ray lasers or are they still the stuff of science fiction ?
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Are their any small X Ray lasers or are they still the stuff of science fiction ?
Like a laser pointer? Science fiction. They have been making them "smaller" meaning they're trying to fit them in a normal-sized room rather than a giant lab, but I think room-sized (or more commonly "tabletop" meaning it can fit on a large optical table) is about cutting edge now. See, for example: http://www.colorado.edu/news/features/cu-boulder-physicists-use-ultrafast-lasers-create-first-tabletop-x-ray-device
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Very interesting JP.
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what I mean .....thermal raddtion like infrared ...light ...and ... ultravoilt...does x ray involve thermal radiation also.
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See reply #2 above. As I said before, it's all the same stuff. What do you mean by "involve"?
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infrared ...light ...and ... ultraviolet...x ray
These are all forms of quantised electromagnetic radiation.
- Infra-red is typically produced by vibrations of atoms in a molecule
- Light is typically produced by an outer electron of an atom making a small changing to its orbital
- Ultraviolet is typically produced by an outer electron making a large change in its orbital
- X-Rays typically occur due to an inner electron changing its orbital
- Gamma rays typically occur due to processes in an atomic nucleus
- ...but there are exceptions and borderline cases, like decay of Technetium 99m (http://en.wikipedia.org/wiki/Technetium-99m) is a nuclear process, but it produces photons in the X-Ray range.
However, all practical methods of producing them are not 100% efficient, so they all produce some heat (infra red), and quite possibly some visible radiation as well. X-Ray targets are bombarded by high-energy electrons, so they get quite hot, and they need to be cooled.
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http://www.colorado.edu/news/features/cu-boulder-physicists-use-ultrafast-lasers-create-first-tabletop-x-ray-device
<<Because X-ray wavelengths are 1,000 times shorter than visible light and they penetrate materials, these coherent X-ray beams promise revolutionary new capabilities for understanding and controlling how the nanoworld works on its fundamental time and length scales,” Murnane said. “Understanding the nanoworld is needed to design and optimize next-generation electronics, data and energy storage devices and medical diagnostics.”
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“As an added advantage, the X-rays emerge as very short bursts of light that can capture the fastest processes in our physical world, including imaging the motions of electrons,” Kapteyn said.
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Laser beams, which are visible light, represent one of the best ways to concentrate energy and have been a huge benefit to society by enabling the Internet, DVD players, laser surgery and a host of other uses.>>
Did they forget to write the military uses of an x-ray laser? :)
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Maybe the military sponsors rejected their funding proposal. ;)
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http://www.colorado.edu/news/features/cu-boulder-physicists-use-ultrafast-lasers-create-first-tabletop-x-ray-device
<<Because X-ray wavelengths are 1,000 times shorter than visible light and they penetrate materials, these coherent X-ray beams promise revolutionary new capabilities for understanding and controlling how the nanoworld works on its fundamental time and length scales,” Murnane said. “Understanding the nanoworld is needed to design and optimize next-generation electronics, data and energy storage devices and medical diagnostics.”
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“As an added advantage, the X-rays emerge as very short bursts of light that can capture the fastest processes in our physical world, including imaging the motions of electrons,” Kapteyn said.
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Laser beams, which are visible light, represent one of the best ways to concentrate energy and have been a huge benefit to society by enabling the Internet, DVD players, laser surgery and a host of other uses.>>
Did they forget to write the military uses of an x-ray laser? :)
What military uses?
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What military uses?
X-ray radiations are very penetrating, no armor, no mirror can stop them. Any portable gun able to deliver x-ray beams vith high intensity would be a terrifying weapon.
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lightarrow
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What military uses?
X-ray radiations are very penetrating, no armor, no mirror can stop them. Any portable gun able to deliver x-ray beams vith high intensity would be a terrifying weapon.
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lightarrow
That's not true. Depending on the amount of radiation one speaks of as "being stopped," the material in question and the wavelength of the x-rays, it's very very possible for x-rays to be stopped. An x-ray (as in the image created by x-ray photons) canbe created because some material stops x-rays more by than other material. A thin sheet of aluminum can stop a great amount of x-rays. That's why you'd see it imaged as white in an x-ray image. Lead is used when a technician takes an x-ray so that extraneous x-rays don't damage repreductive cells. A lead apron is always worn byh surgeons who use x-rays during their work. The amount of penetration of an x-ray beam depends on the material that the target is made of, the energy of x-ray photons and the intensity of the x-ray beam.
So it's quite misleading to say that no armour can stop them. When it comes to intensity even visible light can penetrate matter. When the H-Bomb was tested Bikini Atoll in tghe 50s the observers said that even with their dark googles on they could see through people's body mass like they were looking through a skeleton. Yikes!
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X-ray radiations are very penetrating, no armor, no mirror can stop them. Any portable gun able to deliver x-ray beams vith high intensity would be a terrifying weapon.
That's not true. Depending on the amount of radiation one speaks of as "being stopped," the material in question and the wavelength of the x-rays, it's very very possible for x-rays to be stopped. An x-ray (as in the image created by x-ray photons) canbe created because some material stops x-rays more by than other material. A thin sheet of aluminum can stop a great amount of x-rays. That's why you'd see it imaged as white in an x-ray image. Lead is used when a technician takes an x-ray so that extraneous x-rays don't damage repreductive cells. A lead apron is always worn byh surgeons who use x-rays during their work. The amount of penetration of an x-ray beam depends on the material that the target is made of, the energy of x-ray photons and the intensity of the x-ray beam.
So it's quite misleading to say that no armour can stop them. When it comes to intensity even visible light can penetrate matter. When the H-Bomb was tested Bikini Atoll in tghe 50s the observers said that even with their dark googles on they could see through people's body mass like they were looking through a skeleton. Yikes!
You are quite right but you are missing the point. To make it simple let's consider a metal armor hit with a visible laser and an x-ray laser of the same intensities. If the armor is smooth and reflecting the first will do nothing. And the second? Will the metal stop the beam? If yes (long wavelenghts x-rays), it will not reflect it (excepting at angles of incidence near 90°), so it will absorb it and in a few instants (if the intensity is high) it will be vaporized and pierced...
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lightarrow
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There's a general problem with short wave lasers to do with the lifetime of the upper excited state.
They are always going to be horribly inefficient.
So, the waste heat and other radiation (not least the x rays) from the "X ray gun" will fry the guy firing it at least as fast as the beam will harm the person it's pointed at.
So, as I said, what military applications?
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There's a general problem with short wave lasers to do with the lifetime of the upper excited state.
They are always going to be horribly inefficient.
So, the waste heat and other radiation (not least the x rays) from the "X ray gun" will fry the guy firing it at least as fast as the beam will harm the person it's pointed at.
So, as I said, what military applications?
Premise: I'm not involved in x-ray apparatus engineering, so I don't know how it's made, excepting for very general principles.
For example I know that in x-ray generators they use fast rotating metallic disks at high incidence angles. The principle can...in principle be exploited even better, using more than one disk, higher incidence angles and multiple reflections, together with screens made of tungsten (it's better than lead).
Furthermore, the beam could, I'm still talking in principle, be focalized in exit, with suited mirrors, so the effectiveness as weapon would be at the exit of the gun and not for the soldier using it.
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lightarrow
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I'm also not involved in building or designing x ray kit, but I do know a few things about x ray tubes
1 they are horribly inefficient.
2 they emit x rays in all directions indiscriminately.
Also
3 x rays go through people
So
you need a big heavy high power high voltage source to run the- and the cooling needed to stop the tube melting.
Good luck making that portable.
The tube emits x rays in all directions so all directions apart from "down the barrel" need to be screened.
Whether tungsten or lead is better screening depends on exactly what you are looking at. Tungsten screens are often thinner- but that's mainly because tungsten is a lot denser.
The efficacy for x ray scattering depends on the electron density and lead beats tungsten on a weight for weight basis.
It hardly matters.
The inverse square law makes a lot more difference.
It's reasonable to assume that the person firing the gun is a lot closer to it than the intended victim.
That means his shielding needs to be a lot times a lot more effective.
One of the points already made in favour of Xrays as a beam weapon is that reflecting them is difficult. so " I'm still talking in principle, be focalized in exit, with suited mirrors" is probably a non-starter.
Finally, one of the notable points about Xrays is that they go through people. If they go through, then they didn't deposit any energy in the person they hit.
That reduces their effectiveness compared to, for example, IR (you can choose a wavelength that's well absorbed by the body.)
So, for a given beam power IR works better because more of it is absorbed.
So, remind me, what were the military applications?
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I'm also not involved in building or designing x ray kit, but I do know a few things about x ray tubes
1 they are horribly inefficient.
2 they emit x rays in all directions indiscriminately.
Also
3 x rays go through people
So
you need a big heavy high power high voltage source to run the- and the cooling needed to stop the tube melting.
Good luck making that portable.
The tube emits x rays in all directions so all directions apart from "down the barrel" need to be screened.
Whether tungsten or lead is better screening depends on exactly what you are looking at. Tungsten screens are often thinner- but that's mainly because tungsten is a lot denser.
The efficacy for x ray scattering depends on the electron density and lead beats tungsten on a weight for weight basis.
It hardly matters.
The inverse square law makes a lot more difference.
It's reasonable to assume that the person firing the gun is a lot closer to it than the intended victim.
That means his shielding needs to be a lot times a lot more effective.
BC, you're describing a standard X-ray source that emits vis bremsstrahlung, not an X-ray laser. An X-ray tube has properties similar to a standard incandescent light bulb: it emits photons in all directions and is relatively inefficient. An X-ray laser is still inefficient, but at least it emits X-rays in a collimated, coherent beam. That alleviates some of your concerns as the inverse square law doesn't apply to a coherent beam.
I do work on X-rays and I can tell you a few potential military applications:
1) Portable X-ray phase imaging. Like phase contrast imaging in visible light microscopy, things which aren't visible on standard X-rays can become visible with clever engineering of the imaging system. But as in visible light, coherence is a requirement. DARPA has shown interest in funding these types of projects to provide improved medical imaging in the field.
2) Destroying missiles, satellites, etc. Because its relatively hard to deflect compared to visible lasers, you could use X-rays to shoot down missiles. I'm skeptical of how practical this is, but there have been some prototypes funded and developed by the military. The problem here is high power requirements.
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Our sun produces a lot of X-Rays, and certainly there are hotter stars out there.
Also consider Planck's Law (http://en.wikipedia.org/wiki/Planck%27s_law) and Planck's curves.
Your thermal radiation will have a peak radiation for each temperature. However, it also tends to have "tails" at both the longer and shorter wavelengths. That would seem to indicate that some of the thermal emissions will be at very short wavelengths. Evan suggested that there may be associated atomic changes with the different wavelength emissions.
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One of the points already made in favour of Xrays as a beam weapon is that reflecting them is difficult. so " I'm still talking in principle, be focalized in exit, with suited mirrors" is probably a non-starter.
I wrote how: "high incidence angles".Finally, one of the notable points about Xrays is that they go through people. If they go through, then they didn't deposit any energy in the person they hit.
I wish it was! We wouldn't have any danger for radiographies! Unfortunately the truth is different: they do deposit energy inside. But it's even true that I don't have an idea of which is the percentage of energy deposited...That reduces their effectiveness compared to, for example, IR (you can choose a wavelength that's well absorbed by the body.)
So, for a given beam power IR works better because more of it is absorbed.
When IR is absorbed. But actually is easy to reflect an IR beam.
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lightarrow
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I'm also not involved in building or designing x ray kit, but I do know a few things about x ray tubes
1 they are horribly inefficient.
2 they emit x rays in all directions indiscriminately.
Also
3 x rays go through people
So
you need a big heavy high power high voltage source to run the- and the cooling needed to stop the tube melting.
Good luck making that portable.
The tube emits x rays in all directions so all directions apart from "down the barrel" need to be screened.
Whether tungsten or lead is better screening depends on exactly what you are looking at. Tungsten screens are often thinner- but that's mainly because tungsten is a lot denser.
The efficacy for x ray scattering depends on the electron density and lead beats tungsten on a weight for weight basis.
It hardly matters.
The inverse square law makes a lot more difference.
It's reasonable to assume that the person firing the gun is a lot closer to it than the intended victim.
That means his shielding needs to be a lot times a lot more effective.
BC, you're describing a standard X-ray source that emits vis bremsstrahlung, not an X-ray laser. An X-ray laser is still inefficient, but at least it emits X-rays in a collimated, coherent beam. That alleviates some of your concerns as the inverse square law doesn't apply to a coherent beam.
I know.
There's a reason.
I'm countering a point made by someone else who described their use.
"For example I know that in x-ray generators they use fast rotating metallic disks at high incidence angles."
Re." as the inverse square law doesn't apply to a coherent beam."
Well yes and no.
The beam has a divergence and the on-axis power density (w/m^2) does follow the inverse square law. Since that's the bit that does a lot of the damage...
It is an improvement, but there's still a problem.
Here's a phase contrast image (an optical one).
http://en.wikipedia.org/wiki/File:Brightfield_phase_contrast_cell_image.jpg (http://en.wikipedia.org/wiki/File:Brightfield_phase_contrast_cell_image.jpg)
It's not monochromatic, so they plainly didn't need a laser to produce it.
I think I'd be more scared of firing an x ray laser than I would be of having it pointed at me. I can walk faster than you could track that much hardware.
As far as I'm aware the X ray laser is a nice research toy- but not (at least yet) very practical.
Also, again AFAIA they are even less efficient than the old fashioned vacuum tube.
And I wish the best of luck to anyone trying to do large numerical aperture optics with xrays and grazing incidence mirrors.
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Well this debate's getting a bit silly. But to address two of your points:
1) A laser beam typically has power falls off like 1/z^2 once you get past the Rayleigh distance (z measures distance from the source along the axis of the beam). A point source falls off like 1/z^4. That's why a laser is handy for many things that an LED is not.
2) Phase imaging techniques tend to rely more heavily on spatial coherence (I should have been more precise above). Temporal coherence tends not to be such a big issue. In both cases, you don't need a laser (most of my work uses point sources). Spatial coherence generally impacts your resolution, so you can get away with traditional sources if you don't need diffraction-limited imaging. But the benefits of a laser would be huge because 1/z^2 is much better than 1/z^4.
The point of research is to figure out if it is possible to bring this down to small scale--perhaps for use in medical settings or even smaller scale so that it's easily portable. I'm skeptical, but the research is getting funded and some progress is being made.