Tiny X-rays of Tiny Animals

Johnny Vector writes: "Scientists at Cornell have taken X-rays of fruit flies, with enough detail to see the hairs on their wings. The AIP has more photos. They did it with an "X-Pinch" machine: vaporize a wire, the resulting plasma implodes, producing a tiny (1/1000 inch), fast (nanosecond) pulse of X-rays. I want one of those machines."

Comments

X-rays from ordinary electrical fuses

[Wills]

Any electrical spark of sufficient energy density can generate X-rays as well as emissions in other regions of the EM spectrum, especially visible and UV light. For example, you can also get emissions of X-rays from many types of electrical safety fuses when a massive excess of electrical current causes them to blow.

The X-ray emissions from a fuse are detectable with the help of a well-equipped physics lab. However, the emissions you get are not very useful, being neither of short duration nor a single point source emission. By contrast the researchers at Cornell are using carefully constructed crossed wires which produce extremely short picosecond point-source pulses of X-rays.

Re: X-rays from ordinary electrical fuses

[Wills]

What the previous poster says is completely wrong. You always get X-rays even from ordinary electrical sparks such as from fuses blowing. The ideas explaining this fact have been known since the theories of quantum mechanics were developed in the 20th century.

Planck's Law states there are emissions of electromagnetic radiation at all wavelengths from zero to infinity, i.e. including visible light, infrared, ultraviolet, x-ray, gamma ray, etc.

Planck's Law of Energy Distribution:

• E(L)= 2.PI.h.c^2 / (L^5 (e^(h.c.k.T/L)-1))

where

• E(L) is the energy emitted [Watts/metre^2/UnitWavelength],
  
  L is the wavelength of emitted radiation [metres],
  
  T is the temperature of the black-body emitter [Kelvin],
  
  c is the speed of light (3x10^8 metres/second),
  
  k is Boltzmann's constant (1.38x10E-23 Joules/Kelvin),
  
  h is Planck's constant (6.62606891 x 10E-34 Joule seconds), and
  
  PI is the mathematical constant (3.14159...)

The electromagnetic emissions are strongest at one wavelength given by

Wien's Law

• L = 0.002898 / T

I think the previous poster has confused total energy dissipation with photon energy which is a function of wavelength (another of Planck's laws: E=hc/L). Although the total energy dissipated when a fuse blows is indeed relatively small, c.0.1 Joules, you nonetheless get electromagnetic emissions at all wavelengths including X-rays by Planck's Law.

There is a simple experiment to give a visible indication that a wide range of wavelengths is emitted by electrical sparks. Wearing gloves and safety eye glasses, connect a short 2cm length of 1Amp fuse wire across the two terminals of a low voltage supply like a 12Volt car battery. The fuse wire will blow. Notice the color of the centre of the spark is roughly white. This is because the temperature of the vaporised metal from the fuse wire, created when the fuse blows, momentarily exceeds 5000K, giving a wavelength of peak emission by Wien's Law of 580nm (green light).

• The reason why you don't see the spark as having a green color is that it is emitting a wide range of wavelengths centered around 580nm which stimulates all three types of the color cone receptors in your eyes nearly equally, so making the color appear white. Your eyes lack X-ray and gamma ray detectors, so you cannot see this radiation being emitted by the fuse.

• The reason why you are not much harmed by the emissions of X-rays and gamma rays from the electrical spark is that the total energy of the emissions at the higher frequencies is very small according to Planck's Law, above, even though the energy of individual photons at the higher frequencies is very high (E=hc/L).

If you want to understand more about the electromagnetic spectrum, there is a great summary of the quantum mechanics of black body radiation here

Re:I hope they don't ignite the atmosphere...

[mmontour]

I wonder if some similar technique could be used to produce thermoneuclear fusion.

See, for example, this Scientific American article about "Z-pinch fusion".

Re:"Pinches"

[deglr6328]

It may help to think of a(kindof) common result of the pinch effect. In arc welding, if you get just the right setup with enough current at the weld and a molten bit of metal it will splatter the metal everywhere because of the pinch effect.

The pinch effect is created by the strong axial magnetic field created by the current flowing through the material in question. See here for illustrations of magnetic fields. In the case of the article they used two crossed wires which were vaporized to a plasma(therefore still conducting like a wire) by high current. You can picture the strong magnetic field wraping cylindrically around (and squeezing inward with increasing current) the vaporized wire/plasma's axis. At the intersection of the two wires there would then be a small bubble of highly compressed plasma which is heated to extremely high temperatures, as the plasma cools there is a fast plasma "recombination" where the electrons rejoin their nuclei and emit a fast burst of x-rays.
(IANAP so if someone here is, and there is a mistake anywhere feel free to correct me)

If you instead picture an annular array of wires(eg. 10-20 wires) rather than two crossed wires than you can see that the individual magnetic fields of the wires combine into one huge axial field. This is the so called Z-pinch (because the magnetic field is in the "z" axis). These are the pinches used to initiate thermonuclear fusion in machines like this.

As an aside: Sandia used to use an X-Pinch to "backlight" implosion experiments on the Z-Machine with x-rays so that they may be imaged. Recently they upgraded this setup with a more reliable method of x-ray backlighting using ultrahigh power laser pulses to heat a metal foil target that then creates x-rays. The place where I work supplied the laser parts.